JP6914077B2 - Strain gauge for measuring stress intensity factor with crack monitoring function, stress intensity factor calculation method and crack monitoring method - Google Patents

Description

The present invention relates to a stress gauge for measuring a stress intensity factor and a method for calculating a stress intensity factor having a crack monitoring function, and more specifically, is one of the fracture mechanics parameters of a crack (crack) generated in a member. A dedicated strain gauge designed to eliminate the need for complicated crack length measurement work to easily measure the stress intensity factor and to monitor the progress of cracks, and a strain gauge for measuring the stress intensity factor are used as measurement targets. The present invention relates to a stress intensity factor calculation method and a crack monitoring method, which are attached to the crack tip and can easily and accurately obtain a stress intensity factor.

Conventionally, equipment, stress intensity factor acting on crack (cracks) that Ki present in the structure (referred to as "K value", in fracture mechanics parameters will drive to grow the crack, opening mode K _I and shear mode K _II , K _III ), the calculation uses many assumptions, and complicated calculation is required.
As a conventional technique of such a strain gauge for measuring a stress intensity factor, there is a technique disclosed in Japanese Patent Application Laid-Open No. 63-24103 (hereinafter referred to as "Patent Document 1").
As shown in FIG. 15, the strain gauge for measuring the stress intensity factor described in Patent Document 1 has a diameter at the center of a rectangular sheet-like base 1 made of an insulating material such as paper or synthetic resin. The opening 2 of d is formed. The circumference on the radius r ₁ from the center of the opening 2, is a gauge grid 3 and 4 forming the semicircular arc respectively formed, the lead lines 5 and 6 respectively are connected to both ends of the gauge grid 3,4 ing. Similarly, on the circumference of radius r ₂ from the center of the opening 2, it is a gauge grid 7 and 8 forming the semicircular arc respectively formed, each at both ends leads 9 and 10 of these gauges grids 7,8 It is connected.
The grid patterns of the gauge grids 3, 4, 7, and 8 are set so that the measurement directions of the gauge grids 3, 4 and the measurement directions of the gauge grids 7, 8 are perpendicular to each other.

The strain gauge of Patent Document 1 configured in this way requires complicated calculations in order to calculate the stress intensity factor. For example, a table (or graph) corresponding to the crack length is prepared in advance. There is a drawback that it must be calculated using this table and the measured crack length.
The stress intensity factor could not be calculated without using the above table and the measured strain values.
As another prior art, there is a method in which a large number of rosette type gauges are attached around the crack and the stress intensity factor is calculated from the measured strain value.
However, it is troublesome to attach this large number of rosette type gauges, and the amount of collected strain value data is large, which requires a lot of labor for processing and is difficult to miniaturize. There was a problem that it was difficult to measure in a small area.
In order to deal with such a problem, the Applicant has formed a dedicated small stress intensity factor measuring strain in which a pattern capable of detecting the strain around the crack is formed so as to match the desired stress intensity factor analysis formula. The gauge has been proposed in Japanese Patent Application Laid-Open No. 2015-138020 (hereinafter referred to as "Patent Document 2").
The invention according to Patent Document 2 has the structure shown in FIG. The strain gauge for measuring the stress intensity factor shown in FIG. 16 has the following configuration.

The reference axis OX extending in the radial direction from the axis center O, the first arc portion and the second arc portion having different radii from the axis center O, and the outer side at a predetermined interval from the first and second arc portions. The third arc portion and the fourth arc portion that are located and have different radii from the axis center O, and the first and second radial axes OR1 and that extend in the radial direction at a predetermined angle with the reference axis OX as symmetry. When virtualizing with OR2
Formed in the fan-shaped first and second regions surrounded by the reference axis OX, the first and second radiation axes OR1 and OR2, and the first arc portion and the second arc portion, respectively. The first and second gauge grid portions G1 and G2, which have a sensitive portion in the radial direction,
Formed in the fan-shaped third and fourth regions surrounded by the reference axis OX, the first and second radiation axes OR1 and OR2, and the third arc portion and the fourth arc portion, respectively. The third and fourth gauge grid portions G3 and G4, which have a sensitive portion in the radial direction,
A pair of first connection terminals T1-1 and T1-2 connected to each end of the first gauge grid portion G1 and
A pair of second connection terminals T2-1 and T2-2 connected to each end of the second gauge grid portion G2,
A pair of third connection terminals T3-1 and T3-2 connected to each end of the third gauge grid portion G3, and
A pair of fourth connection terminals T4-1 and T4-2 connected to each end of the fourth gauge grid portion G4, and
The first and second gauge grid portions G1 and G2, the third and fourth gauge grid portions G3 and G4, and the first and second connection terminals T1-1, T1-2 and T2-1, A strain gauge composed of T2-2 and an insulating substrate BP to which the third and fourth connection terminals T3-1, T3-2, T4-1, and T4-2 are integrally attached.
The axis center O is aligned with the crack tip generated in the object to be measured, and the direction of the crack is aligned with the reference axis OX, and the insulating substrate BP is attached to the object to be measured. It is configured so that the strain around the crack can be measured and the stress intensity factor can be calculated.

According to Patent Document 2 configured in this way, a dedicated small strain gauge for measuring stress intensity factor is formed in which a pattern capable of detecting strain around a crack is formed so as to conform to the desired analysis formula of stress intensity factor. Can be provided.
Further, when the strain gauge for measuring the stress intensity factor according to Patent Document 2 is used, a complicated crack length measurement work is not required, and a strain value around the crack can be obtained by a simple measurement work, and the obtained strain value is obtained. Therefore, it is possible to provide a stress intensity factor calculation method that can easily and systematically obtain a stress intensity factor by calculating at the site like a calculator.
Hereinafter, the flow from crack detection to countermeasures when the strain gauge for measuring stress intensity factor according to Patent Document 2 is used is shown in FIGS. 17 to 19, and the problems to be improved in the present invention will be described.

(1) Detection of cracks First, first, cracks are detected by non-destructive inspection such as regular visual inspection and overflow flaw detection test.
(2) Calculation of stress intensity factor Next, as shown in FIGS. 16 and 17 (b), the axial center O of the strain gauge is aligned with the tip of the found crack and attached to the object to be measured.

As shown in FIGS. 5 (a) to 5 (d), each of the first to fourth strain gauges S1 to S4 will be described later. -The first to first gauge grid portions G1 to G4 corresponding to the first to fourth gauge grid portions G1 to G4 are connected to the dynamic strain measuring instrument EDX-3000B for sale and as the load received by the structure changes [FIG. 17 (a)]. The strain detected by each of the strain gauges S1 to S4 of No. 4 is measured [FIG. 17 (b)]. The stress intensity factor is calculated using the four measured strains [FIG. 17 (d)]. The flow of calculating the stress intensity factor is shown in FIGS. 17 (a), (b), (c), and (d).

(3) Prediction of crack growth The fluctuation range ΔK of the stress intensity factor is used for the prediction of crack growth [Fig. 18 (a)]. The relationship between the fluctuation range ΔK of the stress intensity factor and the crack growth rate is shown for each material, for example, as shown in FIG. 18 (b).
In the graph shown in FIG. 18B, ΔKth is the lower limit value and ΔKc is the upper limit value. When ΔK <ΔKth, the crack does not grow. When ΔKth <ΔK <ΔKc, the crack growth rate increases as the fluctuation range ΔK of the stress intensity factor increases. Then, when the upper limit value ΔKc is exceeded, the crack grows at once. As shown in FIG. 18B, the crack growth can be predicted to some extent by using the relationship between the fluctuation range ΔK of the stress intensity factor and the crack growth rate.

(4) Soundness evaluation The soundness is evaluated from the above crack growth prediction results and the judgment criteria set for each structure. As an example, the strength decrease of the structure due to the crack growth is predicted from the crack growth prediction result, and after a certain period (the period determined from the useful life of the structure, the interval of periodic inspection, etc.) has elapsed. The soundness of the structure is evaluated by comparing the decrease in strength of the structure with the safety level determined from the fracture limit of the structure. A schematic diagram of the soundness evaluation is shown in FIG.
(5) Judgment of treatment Determine the countermeasures for cracks based on the soundness evaluation results and the judgment criteria set for each structure. The judgment criteria are shown below.
1) Continuous use (first stage): As a result of crack growth prediction, the strength reduction of the structure meets the safety level set for each structure, and there is sufficient margin.
2) Implementation of continuous inspection (second stage): As a result of crack growth prediction, the decrease in strength of the structure during a certain period specified in the judgment criteria meets the stability criteria, but there is not enough margin.
3) Repair / replacement (third stage): As a result of crack growth prediction, the decrease in strength of the structure does not meet the safety level set for each structure, or it is satisfied within a certain period set by the judgment criteria. What is expected to disappear.

(6) Implementation of treatment For 1), continue use and, if necessary, perform appropriate inspections at the timing of regular inspections.
2) Continue to use, but monitor crack growth by continuous inspection to ensure safety.
3) Cracks that are judged to be repaired / replaced will be repaired / replaced based on the criteria.
As described above, even in the strain gauge for measuring the stress intensity factor according to Patent Document 2, there is a possibility that the gauge pattern is broken due to the growth of the crack and the growth of the crack can be monitored.

However, the gauge pattern shape of the strain gauge for measuring the stress intensity factor described above has a drawback that the pattern disconnection position and the disconnection timing cannot be specified.
Further, in the strain gauge for measuring the stress intensity factor according to Patent Document 2, for example, even when a crack passes through the strain gauge, the crack happens to be in the first and second gauge grid portions. When a crack passes through a gap portion adjacent to G1 and G2 and a gap portion adjacent to the third and fourth gauge grid portions G3 and G4, any grid portion of the strain gauge is cut. Since it is not done, it will be misidentified (false positive) as if the crack did not occur, and a serious situation will occur.
Therefore, there is no certainty in crack growth detection and it cannot be used for monitoring.
Therefore, for continuous monitoring, for example, a crack gauge as shown in Japanese Patent Publication No. 08-8404 (hereinafter referred to as "Patent Document 3") must be separately installed at the same position. It requires cost and effort. In particular, it is an important issue to reduce these costs and labors in infrastructure structures that have deteriorated in recent years and many cracks have been found.

Further, in the strain gauge for measuring the stress intensity factor, the crack growth rate is only a prediction (estimation), and whether immediate repair or replacement work should be performed or judgment by follow-up is sufficient for fatigue cracks. There was an aspect that strict evaluation was not always easy.
Therefore, even if the crack has not progressed so much, there is a tendency to give priority to safety and repair or replace it.
In the case of such a response, it must be said that it is uneconomical from an economic point of view.
The growth of cracks varies significantly depending on the material of the object to be measured, and the external force applied to the object to be measured varies greatly depending on whether it is applied periodically or irregularly. It is difficult.

Japanese Unexamined Patent Publication No. 63-024103 Japanese Unexamined Patent Publication No. 2015-138020 Real Fairness 08-008404 Gazette

The present invention has been made in view of the above problems, and the first object thereof is to be able to detect the strain around the crack and to fit the analysis formula of the stress intensity factor to be obtained. It is an object of the present invention to provide a strain gauge for measuring a stress intensity factor having a dedicated small crack monitoring function in which a pattern capable of monitoring progress is formed.
Further, a second object of the present invention is to use the strain gauge for stress intensity factor measurement according to the present invention, which eliminates the need for complicated crack length measurement work, and is a simple measurement work for strain around the crack. It is an object of the present invention to provide a stress intensity factor calculation method capable of obtaining a stress intensity factor and monitoring a crack from the obtained strain value easily and accurately by a calculation similar to that of a calculator in the field.
Further, a third object of the present invention is that the crack can be reliably detected and the crack progress state can be accurately grasped in view of the problem of the strain gauge for measuring the stress intensity factor. It is an object of the present invention to provide a strain gauge for measuring a stress intensity factor having a crack monitoring function.

Furthermore, a fourth object of the present invention is irregular even if the material of the object to be measured is different or the external force applied to the object to be measured changes periodically. It is an object of the present invention to provide a strain gauge for measuring a stress intensity factor having a crack monitoring function capable of accurately grasping a crack growth state even in such a case.
The fifth purpose is to make it possible to perform the stress intensity factor measurement strain gauge and the crack detection pattern with one gauge, eliminating the need for replacement work between the strain gauge and the crack detection pattern, and reducing costs. It is an object of the present invention to provide a strain gauge for measuring a stress intensity factor having a crack monitoring function capable of achieving reduction.

The strain gauge for measuring a stress intensity factor having a crack monitoring function according to the first aspect of the present invention is to achieve the above-mentioned first to third objects.
The reference axis extending in the radial direction from the center of the axis, the first arc portion and the second arc portion having different radii from the center of the axis, and the first and second arc portions located on the outside at a predetermined interval, said. When imagining the third arc portion and the fourth arc portion having different radii from the axis center and the first and second radial axes extending in the radial direction at a predetermined angle with the reference axis as symmetry,
It is formed in the fan-shaped first and second regions surrounded by the reference axis, the first and second radial axes, the first arc portion and the second arc portion, respectively, in the radial direction. The first and second gauge grid parts having a sensation part, and
It is formed in the fan-shaped third and fourth regions surrounded by the reference axis, the first and second radial axes, the third arc portion and the fourth arc portion, respectively, in the radial direction. A third and fourth gauge grid section having a sensation section, and
A pair of connection terminals connected to each end of the first gauge grid portion,
A pair of second connection terminals connected to each end of the second gauge grid portion,
A third pair of connection terminals connected to each end of the third gauge grid portion,
A pair of fourth connection terminals connected to each end of the fourth gauge grid portion,
A pair of wiring patterns for relay-connecting the first pair of connection terminals and each end of the first gauge grid portion, and a pair of wiring patterns.
A second pair of wiring patterns for relay-connecting the second pair of connection terminals and each end of the second gauge grid portion, and a second pair of wiring patterns.
A third pair of wiring patterns for relay-connecting the third pair of connection terminals and each end of the third gauge grid portion, and a third pair of wiring patterns.
A fourth pair of wiring patterns for relay-connecting the fourth pair of connection terminals and each end of the fourth gauge grid portion, and a fourth pair of wiring patterns.
It is connected in at least one path of the first pair of wiring patterns and the second pair of wiring patterns, and is inside the first arc portion of the first grid portion and the second grid portion. The first crack detection pattern arranged along the
It is connected in at least one path of the third pair of wiring patterns and the fourth pair of wiring patterns, and is inside the third arc portion of the third grid portion and the fourth grid portion. The second crack detection pattern formed along the
The first and second gauge grid portions, the third and fourth cage grid portions, the first and second connection terminals, the third and fourth connection terminals, and the first to first cages. A strain gauge composed of an insulating substrate in which a pair of wiring patterns 4 and the first and second crack detection patterns are integrally attached.
The center of the axis is aligned with the tip of the crack generated in the object to be measured, and the direction of the crack is aligned with the reference axis, and the insulating substrate is attached to the object to be measured.
It is configured so that the strain around the crack can be measured and the stress intensity factor can be calculated.
It is characterized in that the crack growth can be monitored by the stepwise breaking of the first and second crack detection patterns due to the crack.

The strain gauge for measuring a stress intensity factor according to the invention according to claim 2 has the first crack detection pattern of the second pair of connection terminals and the second gauge grid. It is characterized by being connected to each end of the part.
The strain gauge for measuring a stress intensity factor according to the invention according to claim 3 has the second crack detection pattern of the third pair of connection terminals and the third gauge grid. It is characterized by being connected to each end of the part.
In the strain gauge for measuring stress intensity factor having the crack monitoring function according to the fourth aspect of the present invention, the pair of first to fourth connection terminals are connected to each of the first to fourth gauge grid portions. It is characterized in that it is connected to one end of each of them in a one-to-one relationship.
In the strain gauge for measuring stress intensity factor having the crack monitoring function according to the fifth aspect of the present invention, one of the third pair of connection terminals and one of the first pair of connection terminals are Commonly used,
One of the fourth pair of connection terminals and one of the second pair of connection terminals are commonly used.

The strain gauge for measuring a stress intensity factor according to the invention according to claim 6 has an angle formed by the reference axis, the first radiation axis, and the reference axis and the second radiation axis. , Each of which is 90 °.
The strain gauge for measuring the stress expansion coefficient according to the invention according to claim 7 is the first gauge grid of the strain gauge for measuring the stress expansion coefficient having the crack monitoring function according to claim 1. Of the first to fourth strain gauges corresponding to the fourth gauge grid portion, the two strain gauges to which the first and second crack detection patterns are connected and the other two strains. A gauge is inserted into one side of each of the pair of connection terminals of the first to fourth sides, and fixed resistors are inserted into the other three sides to form four Wheatstone bridge circuits. A bridge voltage is applied to each input end of the bridge circuit, and the strain values of the first to fourth strain gauges obtained by measuring the output voltage generated at each output end with a strain measuring instrument are substituted into a predetermined calculation formula. It is characterized in that the stress expansion coefficient in the shear mode can be measured and the crack growth can be monitored.

The stress intensity factor calculation method according to the invention according to claim 8 is the strain gauge for measuring stress intensity factor according to the first claim 1 among the first and second strain gauges. , One strain gauge is inserted through the crack detection pattern and the other strain gauge is directly inserted into one side, and fixed resistors are inserted into the other three sides to form two Wheatstone bridge circuits.
When a bridge voltage is applied to each input end of the Wheatstone bridge circuit, the strain measured by the first gauge grid unit when the voltage output from each output end is measured by a strain measuring instrument is ε _G1 , the above. The strain measured by the second gauge grid is ε _G2 , the material constant in shear mode is J _1, and the first shape constant of the first and second gauge grids is Q ₁ , and the stress expansion coefficient in shear mode is K _II ,
The following conditional expression (1):

It is characterized by satisfying.
However, the material constant J _{1 in the} shear mode is a constant given by the following conditional expression (2), where E is the Young's modulus and ν is the Poisson ratio.

Further, the first shape constants to Q ₁ gauge grid portion is a constant determined by the shape of the gauge grid portion,
Let the radii of the first and second arcs be r ₁ and r ₂ ,
It is a constant given by the following conditional expression (3).

The stress intensity factor calculation method according to the invention according to claim 9 corresponds to the first to fourth gauge grid portions in the strain gauge for measuring stress intensity factor having the crack monitoring function according to claim 1. Of the first to fourth strain gauges, the two strain gauges to which the first and second crack detection patterns are connected and the other two strain gauges are each paired with the first to fourth strain gauges. A circuit is inserted into each side via the connection terminal, and a fixed resistor is inserted into the other three sides to form four Wheatstone bridge circuits.
When a bridge voltage is applied to each input end of the Wheatstone bridge circuit, the strain measured by the first gauge grid unit when the voltage output from each output end is measured by a strain measuring device is ε _G1 , the above. The strain measured by the second gauge grid section is ε _G2 , the strain measured by the third gauge grid section is ε _G3 , the strain measured by the fourth gauge grid section is ε _G4 , and the shear mode. Strain in shear mode, _{where J 1 is the} material constant, _{Q 1} is the first shape constant of the first and second gauge grids, _{and Q 2} is the second shape constant of the third and fourth gauge grids. The magnification factor K _II is
The following conditional expression (4):

It is characterized by satisfying.
However, the material constant J _{1 in the} shear mode is a constant given by the following conditional expression (2), where E is the Young's modulus and ν is the Poisson ratio.

Further, the first shape constants to Q ₁ gauge grid portion is a constant determined by the shape of the gauge grid portion,
Let the radii of the first and second arcs be r ₁ and r ₂ ,
It is a constant given by the following conditional expression (3).

Further, the second shape constants Q ₂ gauge grid portion, the radius of the third and fourth arcuate section as r ₃ and r _4, which is a constant given by the following conditional expression (5).

The method for calculating the stress intensity factor according to the invention according to claim 10 is
Of the first to fourth strain gauges corresponding to the first to fourth gauge grid portions in the strain gauge for measuring stress intensity factor having the crack monitoring function according to claim 1, the first and fourth strain gauges Two strain gauges to which the second crack detection pattern is connected and two other strain gauges are circuit-inserted on one side via each pair of connection terminals of the first to fourth, and the other three. A fixed resistance circuit is inserted on the side to form four sets of Wheatstone bridges.
When a bridge voltage is applied to the input end of each Wheatstone bridge, the strain measured by the first to fourth gauge grids when the voltage output from the output end is measured by a strain measuring device is ε _G1. ~ε _{G4, F 1} the material constant of the opening _mode, the first and second shape constant of the gage grid as _{Q 1} and _{Q 2,} the stress intensity factor _{K I} of the opening mode,
The following conditional expression (6):

It is characterized by satisfying.
However, the material constant F _{1 in the} opening mode is a constant given by the following conditional expression (7), where E is the Young's modulus and ν is the Poisson ratio.

Further, the first shape constants to Q ₁ gauge grid portion is a constant determined by the shape of the gauge grid portion,
Let the radii of the first and second arcs be r ₁ and r ₂ ,
It is a constant given by the conditional expression (3).
It is a constant given by the conditional expression (5), where the radii of the third and fourth arc portions are r ₃ and r _4.
In the crack monitoring method according to the invention according to claim 11, among the first to fourth strain gauges of the first to fourth strain gauges, the first and second crack detection patterns are used. The two connected strain gauges and the other two strain gauges are circuit-inserted on one side via each pair of the first to fourth connection terminals, and fixed resistors are circuit-inserted on the other three sides. To form four Wheatstone bridge circuits,
A bridge voltage is applied to each of the input ends of the four Wheatstone bridge circuits, and the output voltage generated at each output end is measured by the strain measuring instrument. The strain values of the first to fourth strain gauges are being measured. When the crack progresses and the first detection pattern and the second crack detection pattern connected to the first detection circuit connected to the four Wheatstone bridge circuits are broken, the first abnormality occurs. An output and a second abnormal output are generated, and the crack growth state is obtained based on each time interval from the start of measurement to the occurrence of the first abnormal output and the second abnormal output of the structure. It is characterized by being able to be used for soundness evaluation.

In the crack monitoring method according to the invention according to claim 12, the soundness evaluation of the structure individually determines whether or not continuous use is possible and whether or not there is an urgency in repairing or replacing the structure. It is characterized in that it can be evaluated in a targeted manner.

According to the present invention, a dedicated small crack having a pattern formed so that the strain around the crack can be detected and the crack growth can be accurately monitored so as to match the analysis formula of the stress intensity factor to be obtained. It is possible to provide a strain gauge for measuring a stress intensity factor having a monitoring function.
Further, according to the present invention, by using a strain gauge for measuring stress intensity factor having a crack monitoring function, a complicated crack length measurement work is not required, and a strain value around the crack can be obtained by a simple measurement work. From the obtained strain values, it is possible to provide a stress intensity factor calculation method easily and accurately with a calculation similar to that of a calculator in the field, and to calculate the stress intensity factor that can accurately grasp the crack growth state. A method can be provided.
Further, according to the present invention, even if the material of the object to be measured is different, the external force applied to the object to be measured changes periodically, or even if it is applied irregularly, the crack is cracked. It is possible to accurately grasp the progress of In the second stage between the above two stages, it is possible to provide a strain gauge for measuring the stress intensity factor having a crack monitoring function capable of accurately grasping the necessity of replacement.

Further, according to the present invention, the strain gauge for measuring the stress intensity factor and the crack detection pattern can be performed by one gauge, eliminating the work of replacing the strain gauge with the crack detection pattern and reducing the cost. It is possible to provide a strain gauge for measuring a stress intensity factor having a crack monitoring function that can realize reduction.

Schematically arrange the gauge grid pattern and the crack detection pattern of the strain gauge for measuring the stress intensity factor having the crack monitoring function according to the first embodiment and the second embodiment of the present invention. It is a plan view which shows. A plane schematically showing the arrangement of two gauge grid patterns and one crack detection pattern, which form the basis of a strain gauge for measuring stress intensity factor having a crack monitoring function according to the first embodiment of the present invention. It is a figure. An enlarged plan view showing in detail the shape and arrangement of the gauge grid, the crack detection pattern, and the pattern of the connection terminal of the strain gauge for measuring the stress intensity factor having the crack monitoring function according to the first embodiment of the present invention. Is. An enlarged plan view showing in detail the shape and arrangement of the gauge grid, the crack detection pattern, and the pattern of the connection terminal of the strain gauge for measuring the stress intensity factor having the crack monitoring function according to the second embodiment of the present invention. Is. A circuit diagram in the case of performing strain measurement for each gauge grid using the stress intensity factor calculation method according to the present invention is shown, and FIGS. 5 (a) to 5 (d) show the first to fourth gauge grid sections. It shows the circuit diagram in the case of measuring the strain detected by G1 to G4 respectively. It is a circuit diagram which shows the general Wheatstone bridge circuit which inserted the strain gauge on one side of four sides. It is explanatory drawing which shows the xy Cartesian coordinate system developed from the crack tip. It is explanatory drawing which shows the rθ polar coordinate system developed from the crack tip. It is explanatory drawing which shows the state which attached to the body to be measured of the strain gauge for measuring the stress intensity factor which concerns on this invention. It is a simple flow chart for deriving the stress intensity factor which concerns on this invention. It is a flowchart which shows the flow of the fatigue crack evaluation using the strain gauge for stress intensity factor measurement equipped with the crack monitoring function. A plan view showing a state in which a crack starts from the axial center of a strain gauge for measuring a stress intensity factor having a crack monitoring function, passes through a first crack detection pattern, and reaches a second crack detection pattern. Is. Using the same measurement system as the stress intensity factor calculation, the strain output of the first and third strain gauges to which the first and second crack detection patterns are relay-connected, respectively, is output using the interval function of the strain measuring instrument. It is a timing chart which outputs the measurement result at a fixed interval. It is a characteristic diagram showing the relationship between the crack growth and the strength of the structure. The result of crack growth prediction is shown by the broken line of the thin line. It is a top view which shows the circuit structure of the conventional strain gauge for stress intensity factor measurement which concerns on patent document 1. FIG. FIG. 5 is a plan view showing the shape and arrangement of a gauge grid pattern of a conventional strain gauge for measuring stress intensity factor according to Patent Document 2. In the explanatory diagram showing the flow of calculating the stress intensity factor, (a) is a waveform diagram schematically showing the temporal change of the load applied to the object to be measured, and (b) is the stress intensity according to Patent Document 2. A circuit diagram showing a measurement system for measuring a coefficient, (c) is a waveform diagram schematically showing a temporal change of strain which is an output from a strain measuring instrument, and (d) is a time of a calculated stress intensity factor. It is a waveform diagram which shows typically the change. It is a graph which shows the relationship between the stress intensity factor fluctuation width, and the crack growth rate. It is a graph which shows the predictive soundness evaluation from the relationship between the crack growth and the strength of a structure.

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention within the scope of the claims, and each feature described in the embodiments. Not all combinations of are essential for the solution of the present invention.

[First Embodiment and Second Embodiment]
FIG. 1 shows a schematic arrangement of a gauge grid pattern and a crack detection pattern of a strain gauge for measuring a stress intensity factor having a crack monitoring function according to the first embodiment and the second embodiment of the present invention. Is a plan view schematically showing.
FIG. 2 is a plan view schematically showing the arrangement of a part of the basic gauge grid and the crack detection pattern of the strain gauge for measuring the stress intensity factor according to the first embodiment.
FIG. 3 details the shape and arrangement of the gauge grid, the crack detection pattern, and the pattern of each connection terminal of the strain gauge for measuring the stress intensity factor having the crack monitoring function according to the first embodiment of the present invention. It is an enlarged plan view shown in.
FIG. 4 is an enlargement showing the shape and arrangement relationship of the gauge grid, the crack detection pattern, and the pattern of the connection terminal of the strain gauge for measuring the stress intensity factor having the crack monitoring function according to the second embodiment of the present invention. It is a plan view.
FIG. 5 shows a circuit diagram when strain measurement is performed for each gauge grid (strain gauge) using the stress intensity factor calculation method according to the present invention, and FIGS. 5 (a) to 5 (d) show. It is a circuit diagram at the time of measuring the strain detected by each of the 1st to 4th gauge grid sections G1 to G4.

First, with reference to FIG. 2, a strain gauge for measuring a stress intensity factor of a basic portion (hereinafter, referred to as “basic embodiment”) of the first embodiment of the present invention will be described in detail.
As shown in FIG. 2, the strain gauge for measuring the stress intensity factor according to the basic embodiment of the present invention is
A reference axis OX extending in the radial direction from the axis center O, a first arc portion C1 and a second arc portion C2 having different _{radii r 1} and r _{2 from the axis center O, and the reference axis OX are defined as symmetrical.} When imagining the first and second radial axes OR1 and OR2 extending in the radial direction with an angle of (90 ° in this example),
Formed in the fan-shaped first and second regions surrounded by the reference axis OX, the first and second radial axes OR1 and OR2, the first arc portion C1 and the second arc portion C2. It has first and second gauge grid portions G1 and G2 having a sensitive portion in the radial direction.

Further, it has a first crack detection pattern L1 arranged along the inner vicinity of the first arc portion C1 of the first gauge grid portion G1 and the second gauge grid G2.
Further, as shown in FIG. 3, the basic embodiment includes a pair of connection terminals T1-1 and T1-2 connected to each end of the first gauge grid portion G1.
A pair of second connection terminals T2-1 and T2-2 connected to each end of the second gauge grid portion G2,
The first and second gauge grid portions G1 and G2, the first and second connection terminals T1-1, T1-2 and T2-1, T2-2, and the first crack detection pattern L1 are integrated. The first and second strain gauges S1 and S2 in the basic form, which are composed of the insulating substrate BP attached to the above, are completed.

As shown in FIG. 2, the axis center O is matched with the crack tip portion generated in the object to be measured, and the direction of the crack portion is matched with the reference shaft OX to measure the insulating substrate BP. It can be attached to the object, the strains ε ₁ and ε ₂ around the crack can be measured, the stress intensity factor can be calculated, and the crack growth can be monitored by the fracture of the first crack detection pattern L1. It is configured in.
Further, as shown in FIGS. 1 and 3, the stress gauge for measuring the stress intensity factor having the crack monitoring function of the first embodiment according to the present invention includes a reference axis OX extending in the radial direction from the axis center O. , located outside from said axis center O radius r ₁ and r ₂ are different first arcuate portion C1 and the first and second arcuate portions C2, apart a predetermined distance from the second arcuate section C1, C2, _{The third arc portion C3 and the fourth arc portion C4 having different radii r 3} and r ₄ from the axis center O, and the first and second arc portions C4 extending in the radial direction at a predetermined angle with the reference axis OX as symmetry. When the radial axes OR1 and OR2 are virtualized
Within the fan-shaped first and second regions surrounded by the reference axis OX, the first and second radiation axes OR1 and OR2, the first arc portion C1 and the second arc portion C2. The first and second gauge grid portions G1 and G2, which are formed and have a sensitive portion in the radial direction, respectively,
Within the fan-shaped third and fourth regions surrounded by the reference axis OX, the first and second radial axes OR1 and OR2, the third arc portion C3, and the fourth arc portion C4. Third and fourth gauge grid portions G3 and G4, which are formed and have sensitive portions in the radial direction, are formed.

Further, as shown in FIG. 3, connection terminals are connected to the first to fourth gauge grid portions G1 to G4, respectively.
That is, the first pair of connection terminals T1-1 and T1-2 connected to each end of the first gauge grid portion G1 and
A pair of second connection terminals T2-1 and T2-2 connected to each end of the second gauge grid portion G2,
A pair of third connection terminals T3-1 and T3-2 connected to each end of the third gauge grid portion G3, and
The fourth pair of connection terminals T4-1 and T4-2 connected to each end of the fourth gauge grid portion G4 are connected, respectively.

Further, a first pair of wiring patterns for relay-connecting the first pair of connection terminals T1-1 and T1-2 and each end of the first gauge grid portion G1 and a pair of wiring patterns.
A second pair of wiring patterns for relay-connecting the second pair of connection terminals T2-1 and T2-2 and each end of the second gauge grid portion G2, and a pair of wiring patterns.
A third pair of wiring patterns for relay-connecting the third pair of connection terminals T3-1 and T3-2 and each end of the third gauge grid portion G3, and a third pair of wiring patterns.
A fourth pair of connection terminals T4-1 and T4-2 and a fourth pair of wiring patterns for relay-connecting each end of the fourth gauge grid portion G4 are formed.
The first pair of wiring patterns and at least one of the second pair of wiring patterns (in this case, the second wiring pattern) are connected to each other in the path of the first gauge grid portion G1 and the second wiring pattern. A first crack detection pattern L1 arranged along the inner vicinity of the first arc portion C1 of the gauge grid portion G2 of the above.
The third pair of wiring patterns and at least one of the fourth pair of wiring patterns (in this case, the third wiring pattern) are connected to each other in the path of the third gauge grid portion G3 and the fourth. A second crack detection pattern L2 formed along the inner vicinity of the third arc portion C3 of the gauge grid portion G4 of the above is formed.

The first and second gauge grid portions G1 and G2, the third and fourth cage grid portions G3 and G4, and the first and second connection terminals T1-1, T1-2 and T2-1, T2-2, the third and fourth connection terminals T3-1, T3-2 and T4-1, T4-2, the first to fourth pair of wiring patterns, and the first and second A strain gauge composed of an insulating substrate BP in which crack detection patterns L1 and L2 are integrally attached.
The axis center O is aligned with the crack tip generated in the object to be measured, and the direction of the crack is aligned with the reference axis OX, and the insulating substrate BP is attached to the object to be measured.
It is configured so that the strain around the crack can be measured and the stress intensity factor can be calculated.
It is characterized in that the crack growth can be monitored by the stepwise fracture of the first and second crack detection patterns L1 and L2 due to the crack (corresponding to claim 1).

In the first embodiment, the first crack detection pattern L1 is connected between the second connection terminal 2-1 and one end of the second gauge grid portion G2 (claim 2). handle).
As its basic configuration, the strain gauge for measuring the stress intensity factor of the present invention is developed in the radial direction in a fan-shaped region developed at 90 ° around the crack tip as shown in FIG. An example of providing a sensation part is shown. With this configuration, the strain generated in the radial direction from the center O is measured, but it is not necessarily limited to 90 °.
FIG. 3 is a plan view including a gauge grid of a strain gauge for measuring a stress intensity factor, which is more specific according to the first embodiment of the present invention. When measuring the stress intensity factor, the user attaches this strain gauge so that its axis center O is aligned with the crack tip and the reference axis OX is in the crack extension direction.

As shown in detail in FIG. 3, the gauge grids G1 to G4 of the strain gauge for measuring the stress intensity factor according to the first embodiment of the present invention are strains generated in the radial direction centering on the crack tip. A first gauge grid portion G1 is provided in the first region, a second gauge grid portion G2 is provided in the second region, and a third gauge is provided in the third region. A grid portion G3 is provided, and a fourth gauge grid portion G4 is provided in the fourth region. The gauge grid portions G1, G2, G3, and G4 each include a sensitive portion developed in the radial direction around the crack tip portion. In FIG. 3, the structure of the sensitive portion extends in the radial direction and has a plurality of folds sequentially in the vicinity of the first and second arc portions C1 and C2 and the third and fourth arc portions C3 and C4. A linear sensation element is arranged. The structure of the sensitive portion of the present invention is not limited to that shown in FIG. 3, as long as it can sense the strain generated in the radial direction centering on the crack tip portion. One end of the linear sensation element of the first gauge grid portion G1 is connected to one first connection terminal T1-1 via one of the first wiring patterns, and the other end is connected to the first connection terminal T1-1. It is connected to the other first connection terminal T1-2 via the other of the wiring pattern of.

One end of the linear sensation element of the second gauge grid portion G2 is connected to one of the second wiring patterns and one of the second connection terminals T2-1 via the first crack detection pattern L1. One end of the second connection terminal T2-2 is connected to the other second connection terminal T2-2 via the other of the second wiring pattern, and one end of the linear sensitive element of the third gauge grid portion G3 is of the third wiring pattern. One is connected to the third connection terminal T3-1, and the other end is connected to the other of the third wiring pattern and the other third connection terminal T3-2 via the second crack detection pattern L2. One end of the linear sensation element of the fourth gauge grid portion G4 is connected to one of the fourth connection terminals T4-1 via one of the fourth wiring patterns, and the other end is of the fourth. It is connected to the other fourth connection terminal T4-2 via the other of the wiring patterns.

The configuration of the first to fourth gauge grid portions G1 to G4 described above can cover the entire strain in the front region of the crack tip.
Any resistance material can be applied to the resistance material forming each of the first to fourth gauge grid portions G1 to G4. For example, Cu—Ni (based) alloys, Ni—Cr (based) alloys, Fe—Cr (based) alloys and the like can be used according to the intended use.
The arrangement of the gauge grid of the strain gauge for measuring the stress intensity factor according to the first embodiment of the present invention is the strain gauge for measuring the stress intensity factor having the crack monitoring function according to the basic embodiment shown in FIG. This is a partial additional arrangement added to the arrangement of the gauge grid and crack detection pattern of. Specifically, the arrangement of the gauge grid of the strain gauge for measuring the stress intensity factor according to the first embodiment of the present invention is the arrangement of the gauge grid of the strain gauge for measuring the stress intensity factor according to the basic embodiment shown in FIG. _{In addition, the third arc portion C3 and the fourth arc portion C4 whose radii are different from r 3} and r ₄ , respectively, and the first radiation axis OR1 and the second radiation axis OR2 with the axis center O as the center. It has a fan-shaped region surrounded by, that is, a third gauge grid portion G3 and a fourth gauge grid portion G4.

The first gauge grid portion G1, the second gauge grid portion G2, the third gauge grid portion G3, and the fourth gauge grid portion G4 are each received in the radial direction with the crack tip portion as the center. It has a feeling part.
In FIG. 3, as the structure of the sensitive portions of the first to fourth gauge grid portions G1 to G4, a plurality of folding points are sequentially formed in the vicinity of the arc portions C1, C2 and C3, C4 extending in the radial direction from the axis center. Although the sensitive element is arranged, the structure of the sensitive portion of the present invention generally only needs to be able to sense the strain generated in the radial direction around the crack tip portion, and therefore, as shown in FIG. Not necessarily what is shown. The configuration of the first to fourth gauge grid portions G1 to G4 described above can cover the entire strain in the front region of the crack tip.

[Second Embodiment]
The arrangement of the gauge grid and the arrangement of the crack detection pattern of the strain gauge for measuring the stress intensity factor having the crack monitoring function according to the second embodiment of the present invention are the same as those of the first embodiment described above. However, the shape and arrangement of the crack detection pattern and each connection terminal are different for each wiring pattern.
For example, regarding the connection terminals, in the first embodiment, eight connection terminals of a pair of first connection terminals T1-1 and T1-2 to a pair of fourth connection terminals T4-1 and T4-2. However, the second embodiment is different in that it is composed of six connection terminals.

As shown in detail in FIG. 4, the gauge grids G1 to G4 of the strain gauge for measuring the stress intensity factor according to the second embodiment of the present invention are strains generated in the radial direction centering on the crack tip. A first gauge grid portion G1 is provided in the first region, a second gauge grid portion G2 is provided in the second region, and a third gauge is provided in the third region. A grid portion G3 is provided, and a fourth gauge grid portion G4 is provided in the fourth region. The gauge grid portions G1, G2, G3, and G4 each include a sensitive portion developed in the radial direction around the crack tip portion. In FIG. 4, the structure of the sensitive portion extends in the radial direction and has a plurality of folds in the vicinity of the first and second arc portions C1 and C2 and the third and fourth arc portions C3 and C4. A linear sensation element is arranged.

The structure of the sensitive portion of the present invention is not limited to that shown in FIG. 4, as long as it can sense the strain generated in the radial direction centering on the crack tip portion.
One end of the linear sensation element of the first gauge grid portion G1 is connected to one of the first connection terminals T1-1 / T3-2 via one of the first wiring patterns, and the other end. Is connected to the other first connection terminal T1-2 via the other of the first wiring pattern. One end of the linear sensation element of the second gauge grid portion G2 is connected to one of the second wiring patterns and one of the second connection terminals T2-1 via the first crack detection pattern L1. One end of the second connection terminal T2-2 / T4-1 is connected to the other second connection terminal T2-2 / T4-1 via the other of the second wiring pattern, and one end of the linear sensation element of the third gauge grid portion G3 is a third. To one of the third connection terminals T3-1 via one of the wiring patterns of the above, and the other end of the other end of the third wiring pattern is connected to the other of the third wiring patterns and the third connection of the other via the second crack detection pattern L2. At the terminals T1-1 / T3-2, one end of the linear sensitive element of the fourth gauge grid portion G4 is connected to the fourth connection terminal T2-2 / T4 via one of the fourth wiring patterns. -1, the other end is connected to the other fourth connection terminal T4-2 via the other of the fourth wiring pattern, respectively.

The configuration of the first to fourth gauge grid portions G1 to G4 described above can cover the entire strain in the front region of the crack tip.
Any resistance material can be applied to the resistance material forming each of the first to fourth gauge grid portions G1 to G4. For example, Cu—Ni (based) alloys, Ni—Cr (based) alloys, Fe—Cr (based) alloys and the like can be used according to the intended use.
The arrangement of the gauge grid of the strain gauge for measuring the stress intensity factor having the crack monitoring function according to the second embodiment of the present invention shown in FIG. 4 is the crack according to the first embodiment shown in FIG. This is a partial change in the wiring pattern, crack detection pattern, and connection terminal configuration of a strain gauge for measuring stress intensity factor with a monitoring function.
The first gauge grid portion G1, the second gauge grid portion G2, the third gauge grid portion G3, and the fourth gauge grid portion G4 are each received in the radial direction with the crack tip portion as the center. It has a feeling part.
In FIG. 4, as the structure of the sensitive portions of the first to fourth gauge grid portions G1 to G4, a plurality of folding points extend in the radial direction from the center of the axis, and a plurality of folding points are sequentially formed in the vicinity of the arc portions C1, C2 and C3, C4. Although the sensitive element is arranged, the structure of the sensitive portion of the present invention generally only needs to be able to sense the strain generated in the radial direction around the crack tip portion, and therefore, as shown in FIG. Not necessarily what is shown. The configuration of the first to fourth gauge grid portions G1 to G4 described above can cover the entire strain in the front region of the crack tip.

[Third Embodiment]
FIG. 5 shows a circuit diagram when strain measurement is performed for each gauge grid using the stress intensity factor calculation method according to the present invention, and FIGS. 5 (a) to 5 (d) show a first gauge. The circuit diagram in the case of measuring the strain detected in each of the grid parts G1 to the fourth gauge grid part G4 is shown.
The first to fourth gauge grid portions G1 to G4 are inserted and connected to one side of the Wheatstone bridge used in the stress intensity factor calculation method according to the present invention, respectively. A resistor R having the same resistance value is inserted and connected to the other three sides of the Wheatstone bridge. More specifically, in the circuit shown in FIG. 5A, a first gauge grid unit connected between one first connection terminal T1-1 and the other first connection terminal T1-2. G1 constitutes one side of the Wheatstone bridge. Similarly, in the circuit shown in FIG. 5B, the second gauge grid portion G2 connected between one second connection terminal T2-1 and the other second connection terminal T2-2 is In the circuit shown in FIG. 5 (c), the third gauge grid portion G3 connected between one third connection terminal T3-1 and the other third connection terminal T3-2 is shown in FIG. 5 (c). In the circuit shown in d), the fourth gauge grid portion G4 connected between one fourth connection terminal T4-1 and the other fourth connection terminal T4-2 is one side of the Wheatstone bridge, respectively. To configure.

The method for calculating the stress intensity factor in the shear mode according to the third embodiment of the present invention uses only the circuits shown in FIGS. 5 (a) and 5 (b). In this case, the strain measurement method is as follows: First, in the circuit shown in FIG. 5A, a bridge voltage e _i is applied to the input end of the Wheatstone bridge, and the strain ε _G1 is calculated using the output voltage value e _{oG1 at this time.} obtain. Next, in the circuit shown in FIG. 5B, a bridge voltage e _i is applied to the input end of the Wheatstone bridge, and the strain ε _G2 is obtained using the output voltage value e _{oG2 at this time.} Finally, the _{stress intensity factor in the shear mode is calculated by substituting the strains ε G1} and ε _G2 into a predetermined arithmetic expression (described later as the principle of this strain measurement method). The above measurement order may be reversed, or the above measurement may be performed at the same time.
Using two of the circuit shown in FIGS. 5 (a) and 5 (b), strain epsilon _G1, and calculates the epsilon _G2, a material constant shear mode and _{J 1,} the shape constant of the gage grid portion G1, G2 As Q1, the stress intensity factor K _II to be obtained is calculated by the conditional equation (1) (corresponding to claim 8).

However, in the conditional expression (1), the material constants J ₁ shear mode, a longitudinal elastic modulus E, the Poisson's ratio [nu, calculated according to the conditional expression (2).

Further, the first shape constant Q ₁ of the gauge grid portion is a _{constant determined by the shapes of the gauge grid portions G 1} and G _2. Specifically, the radius of the first arc portion C1 is r ₁ . It is calculated by the conditional expression (3), _{where r 2} is the radius of the second arc portion C2.

[Fourth Embodiment]
In the stress intensity factor calculation method according to the fifth embodiment, a strain gauge is inserted into a circuit on one side, and a fixed resistor R is inserted into the circuit on the other three sides to form four Wheatstone bridge circuits.
Upon application of a bridge voltage e _i to the input terminals of the Wheatstone bridge circuit, measured by the first gauge grid portion G1 as measured by the measuring instrument strain voltage e _OG1 to e _OG4 outputted from the output terminals The strain _{measured is ε G1} , the strain measured by the second gauge grid section G2 is ε _G2 , the strain measured by the third gauge grid section G3 is ε _G3 , and the strain measured by the fourth gauge grid section G4 is ε G3. Let the measured strain be ε _G4 . The material constants of the shear mode J _1, second shape of said first and first shape constant of the second gauge grid portions G1 and G2 Q _1, said third and fourth gauge grid unit G3 and G4 a constant as _{Q 2,} the stress intensity factor _{K II} shear mode,
The following conditional expression (4):

A method for calculating a stress intensity factor (corresponding to claim 9), which is characterized by satisfying.
However, the material constant J _{1 in the} shear mode is a constant given by the following conditional expression (2), where E is the Young's modulus and ν is the Poisson ratio.

Further, the first shape constants to _{Q 1} gage grid portion G1, G2 are constants determined by the shape of the gauge grid portion G1, G2,
The radius C1 and C2 of the first and second arcuate portions as _{r 1} and _{r 2,}
It is a constant given by the following conditional expression (3).

Further, the second shape constants Q ₂ gauge grid portion, the radius of the third and fourth arcuate section C3 and C4 as r ₃ and r _4, which is a constant given by the following conditional expression (5).

[Fifth Embodiment]
The stress intensity factor calculation method according to this embodiment is a calculation method for specifically obtaining the stress intensity factor in the opening mode by using the above-mentioned first to fourth gauge grid portions G1 to G4.
The stress intensity factor calculation method according to the fifth embodiment of the present invention uses the four circuits shown in FIGS. 5 (a) to 5 (d).
In this case, the strain measuring method is first described in FIGS. 5 (a) to 5 by the same strain measuring method as the strain measuring method used in the stress intensity factor calculation method in the shear mode according to the fourth embodiment of the present invention. _{The first to fourth strains ε G1 to ε G4} are calculated using the four circuits shown in (d). The material constants of the opening mode with the F _1, the first to the first shape constant of the fourth gauge grid portion G1~G4 the Q ₁ and second shape constant as Q _2, the stress intensity factor of the opening mode determining K _I is calculated by the conditional expression (6) (corresponding to claim 10).

However, in the conditional equation (6), the material constant F ₁ in the opening mode is calculated by the conditional equation (7) with the Young's modulus as E and the Poisson ratio as ν.

Further, the first shape constant Q1 of the gauge grid portion is a shape constant determined by the shapes of the first and second gauge grid portions G1 and G2, and specifically, the radius of the first arc portion C1 is set. It is calculated by the conditional expression (3) as described above, where _{r 1} is set and the radius of the second arc portion C2 is r _2. Further, the second shape constant Q2 of the gauge grid portion is a constant determined by the shapes of the third and fourth gauge grid portions G3 and G4, and specifically, the radius of the third arc portion C3 is r. ₃ and then, the radius of the fourth arcuate section C4 as _{r 4,} is calculated by the following conditional expression (5).

(Principle of strain measurement method)
Hereinafter, the principle of the strain measurement method using the Wheatstone bridge circuit according to each of the above embodiments will be described.
FIG. 6 is a circuit diagram showing a general Wheatstone bridge circuit.
Generally, a Wheatstone bridge circuit as shown in FIG. 6 is used for measuring strain with a strain gauge. In the Wheatstone bridge circuit shown in FIG. 6, one of the resistors occupying one side of the Wheatstone bridge circuit _{is replaced with a strain gauge having a resistance value of R g} , and each of the three resistors occupying the other three sides is replaced with a fixed resistance having a resistance value of R. do.
_{The relationship between the resistance value change ΔR g} and the strain ε when the strain gauge receives the strain ε is expressed by the mathematical formula (8).

When only a change resistance [Delta] R _g undergoing strain strain gauge while applying a bridge voltage of e _{i (E)} to the input end of the Wheatstone bridge circuit, the relationship between ε and strain output voltage e _o of the Wheatstone bridge circuit Is expressed by the formula (9).

As measured by strain gauges, upon application of any applied voltage e _{i (E)} in a Wheatstone bridge circuit, by using the output voltage e _o and formulas to be measured (9), obtains the strain ε the strain gauge is subjected ..
However, in FIG. 6 and the above formula,
R _g : Strain gauge resistance,
ΔR _g : Amount of change in resistance value of strain gauge,
K _s : Strain gauge gauge ratio,
ε: Strain received by the strain gauge,
e _i (E): Applicable voltage of Wheatstone bridge circuit, e _o : Output voltage,
R: The resistance value of the fixed resistance.

(Calculation method of stress intensity factor)
Hereinafter, a method of calculating the stress intensity factor using the Wheatstone bridge circuit according to each of the above embodiments will be described.
_{By substituting the strains ε G1 to ε G4} measured by the strain gauge grids G1 to G4 into the mathematical formulas (6) and (1), two types of stress intensity factors are obtained.
The stress intensity factor of the opening mode I K _I
Then, the following equation (6):

Assuming that the stress intensity factor of shear mode II is K _II ,

Below, the measured values are
ε _G1 : Strain measured by the first gauge grid section G1
ε _G2 : Strain measured by the second gauge grid section G2,
ε _G3 : Strain measured by the third gauge grid section G3,
ε _G4 : Strain measured by the 4th gauge grid section G4,
Of these, _{two are ε G1} and ε _G2 , or four are ε _G1 , ε _G2, ε _G3 and ε _G4 .
In addition, the constant determined by the material to be measured is
F ₁ : Material constant in aperture mode,
J ₁ : Material constant in shear mode,
There is.

Furthermore, the constants determined by the shape of the gauge grid
Q ₁ : Strain gauge grid shape constant 1 (Equation 3),
Q _2: strain gauge grid shape constant 2 (Equation 5),
There is.
The above four measured values (ε _G1 , ε _G2 , ε _G3 , ε _{G4 ) and the above four constants (F 1} , J ₁ , Q ₁ , Q ₂ ) predetermined by the material to be measured and the shape of the strain gauge grid. ), It is possible to obtain the stress intensity factors of the two modes.
The material constant F _{1 in the} opening mode is calculated by the equation (7), where E is the Young's modulus and ν is the Poisson's ratio.

The material constant J _{1 in the} shear mode is calculated by the mathematical formula (2).

The shape constant 1 (Q ₁ ) of the strain gauge grid is the radius from the axis center O of the first gauge grid portion G1 and the first and second arc portions C1 and C2 of the second gauge grid portion G2, respectively. Let r ₁ and r _2, and let the radii from the axis center O of the third and fourth arc portions C3 and C4 of the third gauge grid portion G3 and the fourth gauge grid portion G4 be r ₃ and r ₄ , respectively. Calculate with the formula (3).

Second shape constant second strain gauge grid _{(Q 2)} is calculated by Equation (5).

(Derivation of mathematical formula)
FIG. 7 is an explanatory diagram showing an xy Cartesian coordinate system developed from the crack tip.
In the strain gauge of the present invention, two modes, opening mode I and shear mode II, are considered.
As shown in FIG. 7, the strain distribution formula around the crack tip of the material that receives each mode is generally given as a series expansion formula of the distance r from the crack tip in the Cartesian coordinate system of xy. The stress intensity factor appears as a coefficient of the strain distribution equation.
FIG. 8 is an explanatory diagram showing an rθ polar coordinate system developed from the crack tip.
Unlike the conventional gauge, the strain gauge of the present invention performs polar coordinate conversion of the strain distribution formula as shown in FIG. 8 in order to measure the strain in the radial direction centered on the crack tip.
FIG. 9 is an explanatory diagram when strain measurement is performed using the strain gauge for measuring stress intensity factor according to the present invention.
From the two items of the strain distribution subjected to polar coordinate transformation and the shape of the strain gauge according to the present invention shown in FIG. 9, _{the formulas of the strains ε G1 to ε G4} measured by the gauge grid in each mode are the opening mode I. Then, the formulas (10) to (13) are obtained, and in the shear mode II, the formulas (14) to (17) are obtained.

Here, for the sake of simplicity, it is replaced as follows. However, E is the Young's modulus and ν is the Poisson ratio.

As shown in the above equation, F ₁ and J ₁ are values determined by the material-specific Young's modulus E and Poisson's ratio ν. As described above, F ₁ is the material constant in the opening mode and J ₁ is the material in the shear mode. Called a constant.
Also, Q ₁ and Q ₂ are a value determined by the shape of the strain gauge grid, as described above, is referred to as a shape constant second strain gauge grid shape constant 1, Q ₂ of the strain gauge grid Q _1.
Since F ₂ and B ₀ are finally erased by the following derivation, detailed description thereof will be omitted.

(Superposition of opening mode I and shear mode II)
Generally, the crack is considered to be strained as a mixed mode in which the opening mode I and the shearing mode II are combined. Therefore _{, in the following, for the strains ε G1 to ε G4} , the opening mode I and the shearing mode II are overlapped. A case of performing matching will be described.
In this case, mathematical formulas (19) to (22) are obtained.
ε _G1 = F ₁ K _I Q ₁ + F ₂ B ₀ + J ₁ K _II Q ₁ (19)
ε _G2 = F ₁ K _I Q ₁ + F ₂ B _0- J ₁ K _II Q ₁ (20)
ε _G3 = F ₁ K _I Q ₂ + F ₂ B ₀ + J ₁ K _II Q ₂ (21)
ε _G4 = F ₁ K _I Q ₂ + F ₂ B _0- J ₁ K _II Q ₂ (22)
Stress intensity factor _{K I} of opening mode I, when shown in a formula calculation, from the formula (19) + Formula (20), subtracting equation (21) + Formula (22), to organize the results for _{K I} Is obtained as in the formula (6).

Further, the stress intensity factor K _II in the shear mode II can be obtained by subtracting the mathematical formula (20) from the mathematical formula (19) and _{arranging the results for the K II.}

Further, the stress intensity factor _{K II} shear mode II, when shown in a formula calculation, by subtracting equation (20) + Formula (22) from Equation (19) + Formula (21), to organize the results for _{K II} Therefore, it can be obtained as in the formula (4).

FIG. 10 is a flowchart showing a procedure for calculating a stress intensity factor using the stress intensity factor measuring strain gauge and the stress intensity factor calculation method according to the present invention.
In the calculation procedure shown in FIG. 10, the calculation in each processing block shall be performed with reference to the additional drawings and mathematical formulas.
The present invention is not limited to the embodiments described above and shown in the drawings, and can be variously modified and implemented without departing from the gist of the present invention.
For example, than the radius _r 3, _{r 4} from the axial center O, further sixth gauge grid portion as a radius _{r 5, r 6, r 7} , r 8 ··· like outward, further the seventh gauge grid portion It may be expanded.
Next, the flow from crack detection to countermeasures when the strain gauge for measuring the stress intensity factor having the crack monitoring function of the present invention is used will be described with reference to FIGS. 11 to 14.
FIG. 11 is a flowchart showing a flow of fatigue crack evaluation using a strain gauge for measuring stress intensity factor having a crack monitoring function.

In FIG. 12, the crack starts from the axial center of the strain gauge for measuring the stress intensity factor having a crack monitoring function, passes through the first crack detection pattern, and extends to the second crack detection pattern. It is a top view which shows the state.
FIG. 13 shows the strain output of the first and third strain gauges to which the first and second crack detection patterns are connected, respectively, using the same measurement system as the stress intensity factor calculation, and the interval function of the strain measuring instrument. Is a timing chart showing the results of measurement at regular intervals using.
FIG. 14 is a characteristic diagram showing the relationship between the crack growth and the strength of the structure, and is the result of actual measurement by crack detection using a strain gauge for measuring stress intensity factor having a crack monitoring function according to the present invention. Is indicated by a thick dashed line, and the result of crack growth prediction is indicated by a thin dashed line.
In FIG. 11, first, a crack generated in an object to be measured (structure) is found by a non-destructive inspection such as a regular visual inspection or an eddy current flaw detection test (step 1).

Next, the strain gauges of FIGS. 1 to 4 are adhered to the tip of the found crack by aligning the axis center O and by other means.
In that state, for example, as shown in FIG. 5, a Wheatston bridge circuit BC in which each of the first to fourth strain gauges (gauge grid portions) is inserted on one side is connected to the strain measuring instrument M, and the load change received by the structure. Along with this, the strain detected by each of the first strain gauge to the fourth strain gauge is measured. Using the four measured strains, the stress intensity factor is calculated by a predetermined calculation formula (step S2).
The fluctuation range ΔK of the stress intensity factor is used to predict the crack growth.
The relationship between the fluctuation range ΔK of the stress intensity factor and the crack growth rate varies depending on the material, and an example thereof appears as shown in FIG.

As shown in the graph of FIG. 18, ΔKth is the lower limit value and ΔKc is the upper limit value.
Here, when ΔK <ΔKth, it is determined that the crack does not grow.
Further, when the fluctuation width ΔK is ΔKth <ΔK <ΔKc, it is determined that the crack growth rate gradually increases as ΔK increases.
Then, when ΔK becomes ΔK> ΔKc, it is determined that the crack grows at once.
In this way, the "crack safety evaluation" is performed (step S3).
In step S4, when the fluctuation range ΔK of the stress intensity factor described above becomes larger than ΔKc, it is determined that “repair is necessary” (step S5), and repair is immediately performed (step S6).
In step S3 above, ΔK is ΔK <ΔKth and ΔKth <ΔK <ΔKc.
At this time, it is determined that repair is not necessary (step S7), but follow-up is performed because crack growth may occur (step S8).

In the follow-up observation, the crack detection patterns L1 and L2 according to the present invention are also detected by using the strain measuring instrument used for calculating the stress intensity factor.
Then, the tear timings of the first crack detection pattern L1 and the second crack detection pattern L2 shown in FIGS. 3 to 4 are measured, and the crack growth rate is calculated (step S9).
Whether or not repair is necessary is determined according to the crack growth rate and the crack growth length (step S9).
The above steps S8 to S9 will be described in more detail with reference to FIGS. 12 to 14.
As shown in FIG. 12, the time point at which the axial center O of the strain gauge for measuring the stress intensity factor having a crack monitoring function is aligned with the tip of the crack and adhered is set to t ₀ .
Reference By way in conjunction with the timing chart of FIG. 13, the crack progresses, crosses the first Crack patterns L1, first Crack detection pattern L1 is disconnected at time t _1, the second The strain output of the strain gauge S2 shows a value indicating disconnection, for example, "strain output = 999999", and the growth of cracks can be detected.

After crack detection, the crack growth rate is obtained by dividing the crack growth length obtained from the position dimension of the first crack detection pattern L1 by the time from the start of monitoring to the crack detection pattern L1.
Similarly, the across the crack second Crack detection pattern L2 at time t _2, the second Crack detection pattern L2 is disconnected, the value third strain output indicates disconnection, for example, strain measurement In the instrument, the strain output shows "99999999", and the growth of cracks can be detected.
Looking at this state in FIG. 13, the time and the monitoring start time t ₀ from the monitoring start time t ₀ to time t ₁ the first Crack detection pattern L1 is broken, breaking the second Crack detection pattern L2 since the time until the time t ₂ is measured, from the axial center O, respectively拒離and second eaves拒離to crack detection pattern L2 to the first crack detection pattern L1 in time that is the measurement By removing it, the crack growth rate can be obtained.
In the monitoring, a measurement system for calculating the stress intensity factor is used, and the strain outputs of the second and third strain gauges S2 and S3 to which the first and second crack detection patterns L1 and L2 are connected are used. Use the interval function of the strain measuring device to measure at regular intervals (for example, every day).

From the crack growth state obtained as described above, the treatment is judged again by performing the soundness evaluation again.
When predicting the crack growth state only by the fluctuation range ΔK of the stress intensity factor, for example, as can be seen from the graph of FIG. 14, the characteristics shown by the thin broken line are shown, but the result of the actual measurement by the crack detection. Then, the result is different as shown by the dashed line of the thick line.
That is, by providing the crack detection pattern, the soundness can be evaluated more appropriately.
Moreover, the crack detection pattern can be arranged integrally on a common insulating substrate without impairing the function of the strain gauge for measuring the stress intensity factor, and there is no need to replace the strain gauge for monitoring. The cost reduction effect is enormous.
Further, according to the present invention, even if the material of the object to be measured is different, and even when the load (external force) has no periodicity, the crack growth state can be accurately grasped. For example, in the evaluation of soundness, is it in the first stage where it can be used safely and continuously, is it in the third stage where repair / replacement is urgently needed, or is it in the second stage between the above two stages? At this stage, the need for repair / replacement can be accurately grasped, and uneconomical conditions such as early repair can be corrected due to too much emphasis on safety.

The present invention is not limited to the examples described above and shown in the drawings, and various modifications can be made without departing from the gist of the present invention.
For example, in the above-described embodiment, the first crack detection pattern L1 is connected to the second gauge grid G2, but it may be connected to the first gauge grid G1. Similarly, although the second crack detection pattern L2 is connected to the third gauge grid G3, it may be connected to the fourth gauge grid G4.
Further, in the first and second embodiments, those provided with the first to fourth gauge grids G1 to G4 and the first and second crack detection patterns L1 and L2 have been described. As in the basic embodiment shown in FIG. 2, it may be composed of only the first gauge grid G1, the second gauge grid G2, and the first crack detection pattern L1.
However, it can be said that the first and second embodiments are superior in terms of soundness evaluation ability.
Further, the shape and arrangement position of the first and second crack detection patterns are not limited to those shown in the above-described embodiment, and the point is that the insulating substrate is provided together with the first and second gauge grids. It may be arranged in an arc shape on the upper side, on a certain radius from the axis center O, and near the inside of the first and second gauge grids.

OR1 1st radiation axis OR2 2nd radiation axis OX reference axis O-axis center C1 1st arc part C2 2nd arc part C3 3rd arc part C4 4th arc part G1 to G4 1st to 4th gauge grid portion S1~S4 first to fourth strain gauge r ₁ ~r radius T1-1 from _four axles center O, T1-2 first connection terminal T2-1, T2-2 second connection terminal T3-1, T3-2 Third connection terminal T4-1, T4-2 Fourth connection terminal R Fixed resistance P1 to P3 First to third test pieces L1, L2 First and second crack detection Pattern T1-1 / T3-2 1st / 3rd connection terminal T1-2 1st other connection terminal T2-1 2nd one connection terminal T2-2 / T4-1 2nd / 4th The other connection terminal T4-2 The fourth one connection terminal T3-1 The third other connection terminal BC Wheatstone bridge M Strain gauge

Claims (12)

The reference axis extending in the radial direction from the center of the axis, the first arc portion and the second arc portion having different radii from the center of the axis, and the first and second arc portions located on the outside at a predetermined interval, said. When imagining the third arc portion and the fourth arc portion having different radii from the axis center and the first and second radial axes extending in the radial direction at a predetermined angle with the reference axis as symmetry,
It is formed in the fan-shaped first and second regions surrounded by the reference axis, the first and second radial axes, the first arc portion and the second arc portion, respectively, in the radial direction. The first and second gauge grid parts having a sensation part, and
It is formed in the fan-shaped third and fourth regions surrounded by the reference axis, the first and second radial axes, the third arc portion and the fourth arc portion, respectively, in the radial direction. A third and fourth gauge grid section having a sensation section, and
A pair of connection terminals connected to each end of the first gauge grid portion,
A pair of second connection terminals connected to each end of the second gauge grid portion,
A third pair of connection terminals connected to each end of the third gauge grid portion,
A pair of fourth connection terminals connected to each end of the fourth gauge grid portion,
A pair of wiring patterns for relay-connecting the first pair of connection terminals and each end of the first gauge grid portion, and a pair of wiring patterns.
A second pair of wiring patterns for relay-connecting the second pair of connection terminals and each end of the second gauge grid portion, and a second pair of wiring patterns.
A third pair of wiring patterns for relay-connecting the third pair of connection terminals and each end of the third gauge grid portion, and a third pair of wiring patterns.
A fourth pair of wiring patterns for relay-connecting the fourth pair of connection terminals and each end of the fourth gauge grid portion, and a fourth pair of wiring patterns.
It is connected in at least one path of the first pair of wiring patterns and the second pair of wiring patterns, and is inside the first arc portion of the first grid portion and the second grid portion. The first crack detection pattern arranged along the
It is connected in at least one path of the third pair of wiring patterns and the fourth pair of wiring patterns, and is inside the third arc portion of the third grid portion and the fourth grid portion. The second crack detection pattern formed along the
The first and second gauge grid portions, the third and fourth cage grid portions, the first and second connection terminals, the third and fourth connection terminals, and the first to first cages. A strain gauge composed of an insulating substrate in which a pair of wiring patterns 4 and the first and second crack detection patterns are integrally attached.
The center of the axis is aligned with the tip of the crack generated in the object to be measured, and the direction of the crack is aligned with the reference axis, and the insulating substrate is attached to the object to be measured.
It is configured so that the strain around the crack can be measured and the stress intensity factor can be calculated.
For measuring the stress intensity factor having a crack monitoring function, which is configured so that the growth of the crack can be monitored by the stepwise fracture of the first and second crack detection patterns due to the crack. Strain gauge. The crack according to claim 1, wherein the first crack detection pattern is connected between the pair of connection terminals and each end of the second gauge grid portion. Strain gauge for measuring stress intensity factor with monitoring function. The crack according to claim 1, wherein the second crack detection pattern is connected between the third pair of connection terminals and each end of the third gauge grid portion. Strain gauge for measuring stress intensity factor with monitoring function. The first aspect of claim 1, wherein the pair of first to fourth connection terminals are connected to one end of each of the first to fourth gauge grid portions in a one-to-one relationship. Strain gauge for measuring stress intensity factor with crack monitoring function. One of the third pair of connection terminals and one of the first pair of connection terminals are commonly used.
The stress intensity factor measurement having the crack monitoring function according to claim 1, wherein one of the fourth pair of connection terminals and one of the second pair of connection terminals are commonly used. Strain gauge. The crack monitoring function according to claim 1, wherein the angle formed by the reference axis, the first radiation axis, and the reference axis and the second radiation axis is 90 °, respectively. Strain gauge for measuring stress intensity factor. Of the first to fourth strain gauges corresponding to the first gauge grid portion to the fourth gauge grid portion of the strain gauge for measuring the stress expansion coefficient having the crack monitoring function of claim 1, the first strain gauge. Two strain gauges to which the first and the second crack detection patterns are connected and the other two strain gauges are circuit-inserted on one side via each pair of the first to fourth connection terminals, and the other. A fixed resistor is inserted into the three sides of the circuit to form four Wheatstone bridge circuits, a bridge voltage is applied to each of the input ends of the four Wheatstone bridge circuits, and the output voltage generated at each output end is measured with a strain gauge. By substituting the measured strain values of the first to fourth strain gauges into a predetermined calculation formula, the stress expansion coefficient in the shear mode can be measured and the crack growth can be monitored. A characteristic stress expansion coefficient calculation method. In the strain gauge for measuring a stress intensity factor having the crack monitoring function according to claim 1, one of the first and second strain gauges is used through the crack detection pattern and the other. Insert the strain gauge directly on one side and insert the fixed resistor on the other three sides to form two Wheatstone bridge circuits.
When a bridge voltage is applied to each input end of the Wheatstone bridge circuit, the strain measured by the first gauge grid unit when the voltage output from each output end is measured by a strain measuring instrument is ε _G1 , the above. The strain measured by the second gauge grid is ε _G2 , the material constant in shear mode is J _1, and the first shape constant of the first and second gauge grids is Q ₁ , and the stress expansion coefficient in shear mode is K _II ,
The following conditional expression (1):

A method for calculating a stress intensity factor, which is characterized by satisfying.
However, the material constant J _{1 in the} shear mode is a constant given by the following conditional expression (2), where E is the Young's modulus and ν is the Poisson ratio.

Further, the first shape constants to Q ₁ gauge grid portion is a constant determined by the shape of the gauge grid portion,
Let the radii of the first and second arcs be r ₁ and r ₂ ,
It is a constant given by the following conditional expression (3).

Of the first to fourth strain gauges corresponding to the first to fourth gauge grid portions in the strain gauge for measuring the stress intensity factor according to claim 1, the first and the fourth strain gauges have the crack monitoring function. Two strain gauges to which the second crack detection pattern is connected and the other two strain gauges are circuit-inserted on one side via each pair of the first to fourth connection terminals, and the other three sides. A fixed resistor is inserted into the circuit to form four Wheatstone bridge circuits.
When a bridge voltage is applied to each input end of the Wheatstone bridge circuit, the strain measured by the first gauge grid unit when the voltage output from each output end is measured by a strain measuring device is ε _G1 , the above. The strain measured by the second gauge grid section is ε _G2 , the strain measured by the third gauge grid section is ε _G3 , the strain measured by the fourth gauge grid section is ε _G4 , and the shear mode. Strain in shear mode, _{where J 1 is the} material constant, _{Q 1} is the first shape constant of the first and second gauge grids, _{and Q 2} is the second shape constant of the third and fourth gauge grids. The magnification factor K _II is
The following conditional expression (4):

A method for calculating a stress intensity factor, which is characterized by satisfying.
However, the material constant J _{1 in the} shear mode is a constant given by the following conditional expression (2), where E is the Young's modulus and ν is the Poisson ratio.

Further, the first shape constants to Q ₁ gauge grid portion is a constant determined by the shape of the gauge grid portion,
Let the radii of the first and second arcs be r ₁ and r ₂ ,
It is a constant given by the following conditional expression (3).

Further, the second shape constants Q ₂ gauge grid portion, the radius of the third and fourth arcuate section as r ₃ and r _4, which is a constant given by the following conditional expression (5).

Of the first to fourth strain gauges corresponding to the first to fourth gauge grid portions in the strain gauge for measuring the stress intensity factor according to claim 1, the first and the fourth strain gauges have the crack monitoring function. Two strain gauges to which the second crack detection pattern is connected and the other two strain gauges are circuit-inserted on one side via each pair of the first to fourth connection terminals, and the other three sides. A fixed resistor is inserted into the circuit to form four sets of Wheatstone bridges.
When a bridge voltage is applied to the input end of each Wheatstone bridge, the strain measured by the first to fourth gauge grids when the voltage output from the output end is measured by a strain measuring device is ε _G1. ~ε _{G4, F 1} the material constant of the opening _mode, the first and second shape constant of the gage grid as _{Q 1} and _{Q 2,} the stress intensity factor _{K I} of the opening mode,
The following conditional expression (6):

A method for calculating a stress intensity factor, which is characterized by satisfying.
However, the material constant F _{1 in the} opening mode is a constant given by the following conditional expression (7), where E is the Young's modulus and ν is the Poisson ratio.

Further, the first shape constants to Q ₁ gauge grid portion is a constant determined by the shape of the gauge grid portion,
Let the radii of the first and second arcs be r ₁ and r ₂ ,
It is a constant given by the conditional expression (3).
It is a constant given by the conditional expression (5), where the radii of the third and fourth arc portions are r ₃ and r _4. The first and second strain gauges of the first to fourth strain gauges in the strain gauge for measuring the stress expansion coefficient having the crack monitoring function according to claim 1. Two strain gauges to which the crack detection pattern is connected and the other two strain gauges are circuit-inserted on one side via each pair of the first to fourth connection terminals and fixed to the other three sides. Insert a resistor to form four Wheatstone bridge circuits,
A bridge voltage is applied to each of the input ends of the four Wheatstone bridge circuits, and the output voltage generated at each output end is measured by the strain measuring instrument. The strain values of the first to fourth strain gauges are being measured. When the crack progresses and the first detection pattern and the second crack detection pattern connected to the first detection circuit connected to the four Wheatstone bridge circuits are broken, the first abnormality occurs. An output and a second abnormal output are generated, and the crack growth state is accurately grasped based on each time interval from the measurement start time point to the occurrence time point of the first abnormal output and the second abnormal output. A crack monitoring method characterized in that it can be used for soundness evaluation of a structure. The claim is characterized in that the soundness evaluation of the structure can be individually evaluated as to whether or not continuous use is possible and whether or not there is an urgency in repairing or replacing the structure. 11. The crack monitoring method according to 11.

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