JPH0610645B2 - Stress intensity factor measuring gauge, stress intensity factor measuring method, and remaining life monitoring device for cracked member - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a member having a crack, and a member having a crack-like notch (hereinafter, referred to as a crack) (hereinafter, referred to as a crack). A stress intensity factor measuring gauge for non-destructively measuring the stress intensity factor at the tip of a crack member, a stress intensity factor measuring method, and a remaining life monitoring device for a crack member for monitoring the remaining life of the crack member. .

(Prior Art) Generally, various evaluations are performed based on fracture mechanics in order to safely use a structure having a defect or a crack generated during use.

In particular, today, the concept of the stress intensity factor has been proposed as a parameter representing the stress state near the crack tip of a crack member having a crack that is the basis of fracture mechanics. It became possible to handle the fracture behavior of a cracked member with cracks with practically sufficient accuracy. That is, the stress intensity factors of crack members of various shapes are broken and provided for general use to ensure the safety of the structure.

However, the solution for which the stress intensity factor has been obtained has a relatively simple shape, and many others require numerical analysis using a large-scale computer. However, in an actual structure, there are cases where the numerical analysis considering even cracks cannot be performed accurately due to insufficient computer capacity or unclear boundary conditions.

Therefore, recently, it has been attempted to obtain a stress intensity factor by experimental stress analysis for a defect or a crack generated in an actual structure.

That is, as shown in FIG. 8, a circular thin gauge base 1
Two 3-axis rosette resistance wire strain gauges 12 on top of 1,
The present inventors have already proposed a stress intensity factor measuring gauge formed by fixing 12 (Japanese Patent Application No. 60-2).
16810).

Explaining this gauge pattern in detail, the distance L ₁ between the gauge centers 0 of the triaxial rosette resistance wire strain gauges 12 is
The stress intensity factor is set to 1/10 or less of the total length of the crack or crack-like notch to be measured, and the shortest distance L ₂ between each gauge center 0 and the edge of the gauge base 11 is set to The length is set to 1/10 or less.

Then, using such a stress intensity factor measuring gauge, the stress intensity factor is determined by the ratio exception insertion method (details are shown in FIG. 9) developed by the present inventor. That is, as shown in FIG. 9 (a), a stress intensity factor measuring gauge is attached to the tip of the crack 13 with the gauge base 11, and in this state, the triaxial rosette resistance wire strain gauge 12
The stress at the positions of r ₁ and r ₂ in FIG. Then, the stress value is multiplied by the calibration coefficient obtained for the gauge pattern in advance, and extrapolated to the crack tip (r = 0) as shown in FIG. The stress intensity factor is determined. From the relationship between the stress intensity factor and the fatigue crack propagation rate of the material constant stored in advance, a remaining life monitoring device for evaluating the remaining life of the crack member is proposed.

(Problems to be Solved by the Invention) However, it was necessary to further devise the previous proposal.

That is, in actual structural members, the yield stress
If a stress intensity factor measuring gauge is attached near the very tip of the crack 13 because a stress of about 1/2 or 2/3 is applied, the stress intensity factor calculation accuracy decreases due to plastic deformation of the crack tip. To do. Also, it is a difficult task to attach the stress intensity factor measuring gauge to the specified position from the crack tip.
When the attachment position is displaced, the displacement has a great influence on the calculation accuracy of the stress intensity factor. Furthermore, in the actual evaluation of the remaining life of a fatigue crack, the evaluation accuracy will be extremely poor unless the behavior of the opening / closing port of the fatigue crack is clearly understood. That is, a fatigue crack propagates repeatedly inside and outside due to an external load, but it is always open even when the external load is tensile due to microscopic plastic deformation of the crack surface or oxide generation in the middle of the fatigue crack. However, it is not always the case, and it may be closed, and it is necessary to grasp the effective stress intensity factor range in which the fatigue crack is actually open.

It is strongly desired to realize such high accuracy of measurement and evaluation.

This is because many public machines cannot be stopped when a crack occurs. In addition, even in a machine where emergency stop is not possible, if the machine has a sufficient remaining life and is immediately stopped for repair, a large loss will occur, and cracks will be generated without quantitative remaining life evaluation. Continuing to operate the machine that has caused the risk may cause a major destruction of the machine.

The present invention is made in view of these points, the stress intensity factor at the crack tip of the crack member, a stress intensity factor measurement gauge that can be measured with a simple configuration and with high accuracy, Using this stress intensity factor measurement gauge, a stress intensity factor measuring method that can determine the stress intensity factor and a residual life monitoring of the crack member that can accurately determine and monitor the remaining life of the crack member It is intended to provide a device.

[Structure of Invention]

(Means for Solving Problems) A gauge for stress intensity factor measurement according to the first aspect of the present invention is configured such that two triaxial resistance line strain gauges are mounted on a gauge base with a space therebetween. Is attached in the vicinity of the crack of the crack member, the gauge centers of the two triaxial resistance line strain gauges are arranged on the extension line of the crack.

A second aspect of the present invention is the extension of a crack when two triaxial resistance wire strain gauges are mounted on a gauge base at intervals and the gauge base is attached near the crack of a crack member. A stress intensity factor measuring gauge, which is arranged so that the gauge centers of the two triaxial resistance strain gauges are located on the line, is attached near the crack tip of the crack member, and then each of the above 3 Stress is detected by the axial resistance wire strain gauge, and the following equations (1) and (2) are used based on the detected stress. However, σ _{y | θ = 0} : Tensile stress in the direction orthogonal to the crack propagation direction τ _{xy | θ = 0} : Shear stress r: Distance from the crack tip α _I , α _II : Calibration coefficient T _y : Crack Tensile breaking force when an external force acts on the crack edge T _xy : The shearing force when an external force acts on the crack edge multiplies the detected stress of each triaxial resistance line strain gauge by a calibration coefficient, and this is the crack tip. It is characterized in that the stress intensity factor is obtained by extrapolating to.

A third aspect of the present invention is a crack member residual life monitoring apparatus, in which two triaxial resistance line strain gauges are mounted on a gauge base at intervals, and the gauge base is located near the crack of the crack member. A stress intensity factor measuring gauge, which is arranged so that the gauge centers of the two triaxial resistance line strain gauges are located on the crack extension line when it is attached to the crack extension line near the crack tip of the crack member. A stress intensity factor calculator for pasting and then detecting stress with each of the triaxial resistance wire strain gauges, and a stress intensity factor calculator for calculating the stress intensity factor, and a resistance line for crack opening / closing point measurement newly attached at the crack edge portion. The opening and closing point calculator that calculates the opening and closing points of the crack from the output of the strain gauge, and the effective stress intensity factor range is calculated from this stress intensity factor and the opening and closing point of the crack. The cracked member is compared with the stored material constant. And having an evaluation device for determining the residual lifetime.

(Operation) According to the stress intensity factor measuring gauge of the first aspect of the present invention, two triaxial rosette resistance wire strain gauges are provided, and the distance between the center of each gauge and the crack tip is measured. It can be pasted in the range of 1/10 to 3/10 of the total length. Therefore,
The calibration coefficient calculated from the output of each 3-axis rosette resistance strain gauge does not depend on the width of the crack member, the length of the crack, the inclination angle of the crack with respect to the crack member, etc. The stress intensity factor changes in a substantially straight line according to the change in the distance from the gauge center, and the stress intensity factor with higher accuracy can be measured easily and stably.

According to the stress intensity factor measuring method of the second invention of the present invention,
The stress at a suitable position for extrapolation is detected using the stress intensity factor measuring gauge of the first invention having a simple structure, the detected stress is multiplied by a calibration factor, and the extrapolated to the crack tip,
A highly accurate stress intensity factor can be obtained very easily.

According to the remaining life monitoring apparatus for a crack member of the third invention of the present invention, the stress intensity factor calculator for one of the second aspect is used to detect the stress detected by the stress intensity factor measuring gauge of the first aspect.
The stress intensity factor is calculated based on the stress intensity factor measuring method of the invention, and the opening / closing mouth point of the crack is calculated from the output of the resistance wire strain gauge for measuring the crack opening / closing mouth point by the other opening / closing mouth point calculator. Then, the effective stress intensity factor range is calculated from the calculated stress intensity factor and the opening / closing point of the crack, and the material constant of the crack member stored in advance by the evaluator is compared with the effective stress intensity factor range. The remaining life of the member can be accurately determined.

(Example) Hereinafter, the Example of this invention is described.

First, the basic equations of the ratio exception insertion method for obtaining the stress intensity factor according to the present invention are the following equations (3) and (4).

However, σ _{y | θ = 0} : Tensile stress in the direction orthogonal to the crack propagation direction τ _{xy | θ = 0} : Shear stress r: Distance from the crack tip T _y : When an external force acts on the crack edge T _xy : Shear force when an external force acts on the crack edge However, suffixes A and B show the values relating to the problem for which the stress intensity factor is to be obtained, and B is the preliminary calibration factor. This is a value related to the problem.

The validity of the basic expression of the ratio exception insertion method by the expressions (3) and (4) will be described with reference to FIG.

As shown in FIG. 2, the stress intensity factor of the licking crack 23 in the central portion subjected to uniform tension in the vertical direction has already been determined by Kitagawa, Yuki et al. Using a mapping function. .

Therefore, regarding this problem, the boundary element division as shown in FIG. 2 is performed to perform a numerical analysis using the boundary element method (BEM), and the calibration coefficients α _I and α _II in the equations (3) and (4) are α _I = K _It was calculated as _IB / (σ _{yl θ = 0) B} α _II = K _IIB / (τ _{xyl θ = 0) B.} In this problem, no external force acts on the crack edge, so T _y (0) = T _xy (0) = 0. The result is shown by the solid line in FIG.

In FIG. 3, the calibration coefficient when the opening displacement of the crack proposed by the present invention is used is shown by a broken line for reference, but the calibration coefficient when the opening displacement of the crack is calculated from the crack tip. It can be seen that it is strongly influenced by the distance r. Of course, it is clear from the figure that the calibration coefficient of the present proposal using the stress near the crack tip is also a function of the distance r from the crack tip. From the above, when determining the actual stress intensity factor, use the formula (3)
It is appropriate and effective to use the following equations (5) and (6) in which (4) is rewritten.

Next, the stress intensity factor measuring gauge according to the first aspect of the present invention will be described.

FIG. 1 shows a stress intensity factor measuring gauge 25 which is an embodiment of the first invention. The gauge 25 for measuring the stress intensity factor of the present embodiment comprises two triaxial rosette resistance wire strain gauges 22, 22 on a square thin gauge base 21.
It is formed by fixing. When the gauge center 0 of each triaxial rosette resistance wire strain gauge 22 and the gauge base 21 are attached to the crack member, the distance from the tip of the crack 23 is 2C for the total length 2C of the crack or the like. 1/10 ≤ L ₂
The setting is such that / 2C ≦ (L ₂ + L ₁ ) ≦ 3/10.

For example, when the total length of the crack 23 or the like is about 27.5 mm or more, the stress intensity factor measuring gauge 25 formed with L ₂ = 2.75 mm and L ₁ = 2.5 mm is used for measuring the stress intensity factor. It is effective.

It is also highly effective to insert vertical and horizontal guidelines 24, 24 in the gauge base 21 so that the gauge base 21 can be attached at a predetermined position of the crack tip.

Further, it is effective to attach a uniaxial resistance line strain gauge 26 to the crack edge to determine the opening / closing point of the crack 23.

The reason for determining L ₁ and L ₂ in this way is based on the following reasons.

That is, in the case where the strip 27 having the central licking crack 23 shown in FIG. 2 is subjected to a tensile load, the ratio of the strip width to the crack length 2C / W = 0.2, 0.3, 0.4, 0 ．
5, the inclination angle α of the crack was analyzed by the boundary element method (BEM) in the cases of α = 0 °, 30 °, and 45 °, and the calibration coefficients α _I , α _II
The result calculated by α _I = K _IB / σ _YB α _II = K _IIB / τ _{xyB is} shown by the solid line in FIG.

As a result, r / 2aC <0.3 regardless of the above conditions.
Within the range of 5, the calibration coefficient can be displayed as a single curve without depending on 2C / W or α.

On the other hand, since the resistance wire strain gauge has a certain finite size, it is difficult to measure the stress in the vicinity of the crack 23.

Further, as is clear from FIG. 3, the calibration coefficient becomes slightly small in the vicinity of the very tip of the crack 23, and 0.1 ≦ r / 2C ≦ to approximate the calibration coefficient with a straight line which is easy to handle.
Within the range of 0.3, the stress intensity factor measurement which is almost reasonable and effective can be performed.

Next, a method of measuring the stress intensity factor according to the second aspect of the present invention using the stress intensity factor measuring gauge 25 will be described with reference to FIG.

The crack member 37 used for this measurement is a structural carbon steel (SS4
It is a strip plate made of 1 material and having a thickness of 5 mm. This crack member 3
7 is provided with a notch 33 in the center, and a gauge 25 for measuring the stress intensity factor is attached to the tip of the notch. Then, a tensile load is applied to the crack member 37, and in this state, each 3
Axial rosette resistance wire strain gauge 22 shown in FIG. 9 (b)
The stresses at the positions r ₁ and r ₂ are calculated. Then, from the obtained stress, K _I and K _II at the positions of r ₁ and r ₂ are calculated using the values shown in FIG. 3 as calibration coefficients based on the equations (5) and (6). Then, as shown in FIG. 9 (b), the true stress intensity factor is obtained by extrapolating from the K _I and K _II values of the two points r ₁ and r _{2 to} the value of r = 0.

As described above, the stress intensity factors F ₁ and F calculated by the following equations (7) and (8) from K _I and K _II obtained based on the present invention.
_KII and Kitagawa's analytical solution are compared and shown in the attached table.

As can be seen from this attached table, the stress intensity factor obtained by using the stress intensity factor measuring gauge 25 of the present invention has sufficient precision in terms of engineering.

Next, a third invention of the present invention will be described.

The present invention relates to a stress intensity factor measuring gauge 25 of the first invention.
Is used to calculate the stress, the stress intensity factor is calculated according to the second aspect of the invention, and the residual life of the crack member 37 is determined and monitored from this stress intensity factor.

FIG. 5 shows an embodiment of the present invention, and shows a state in which the remaining life of the crack member 37 is monitored when a crack is caused by a defect in the fillet weld.

In this embodiment, a stress intensity factor measuring gauge 25 and a crack opening / closing point measuring strain gauge 26 are attached to the tip of the crack 13. The stress obtained by the stress intensity factor measuring gauge 25 is sent to the amplifier 38. The amplifier 38 is connected to a stress intensity factor calculator 39 that calculates the stress intensity factor according to equations (5) and (6). Further, in this calculator 39, the strain value measured by the strain gauge 26 for measuring crack opening and closing point is sent to the amplifier 40, and the opening and closing point calculator 41 can perform the method as shown in FIG. The effective stress intensity factor range is also calculated from the result of determining. In this way, the reason why the effective stress intensity factor range must be calculated is that the load is transferred when the fatigue crack is completely closed and the upper and lower surfaces are in contact with each other, so that the range in which the crack is closed is This is because the load is considered not to affect the fatigue damage at the crack tip. The stress intensity factor calculator 39 is connected to an evaluator 43 that compares the calculated effective stress intensity factor range with the material constant of the crack member 37 stored in advance in the memory 42. This evaluator 43
A display unit 44 for displaying a comparison result and an operation controller 45 for issuing an operation stop signal when the evaluator 43 determines that the operation is dangerous are connected to the.

Next, the operation of the present invention will be described.

First, the stress intensity factor measuring gauge 25 detects the stress at the tip of the crack 13, the crack opening / closing point measuring gauge 26 detects the crack edge strain, and the amplifiers 38 and 40 respectively detect the strain. Amplification is performed, and the stress intensity factor calculator 39 and the opening / closing point calculator 41 calculate the stress intensity factor and the crack opening / closing point to calculate the effective stress intensity factor.
In this case, the maximum stress coefficient K _Imax , K accompanying the load change
_The stress intensity factor range was calculated as the difference between _IImax and the minimum stress intensity factors K _Imin and K _IImin. For the mode I component, the crack _{opening /} closing ratio (XY) was calculated as in the following equations (9) and (10).
It is multiplied by / (XZ) to obtain the effective stress intensity factor range (see FIG. 6).

△ K _I = (K _Imax ) K _Imin ) (XY) (XZ) _{・ ・ ・} (9) △ K _II = (K _IImax ) K _{IImin ・ ・ ・} (10) The maximum principal stress theory is applied to the failure condition under mixed mode. The maximum principal stress intensity factor _{ΔK θmax} shown in the following equation (11) is calculated from the equations (9) and (10).

However, Is.

Using such _{ΔK θmax} , the evaluator 43 makes a comparative examination with the material constants built in the memory 42 shown in FIG. 7.

That is, in general, the propagation speed of a fatigue crack depends on the stress intensity factor range, and if the stress intensity factor range is small, the crack propagation velocity slows down and does not propagate at all below a certain limit value ΔK _th . On the other hand, if the stress intensity factor is not large, the crack propagation speed is accelerated, and if it exceeds the limit value ΔK _FC , the crack propagates in an unstable manner and the crack member 37 is broken. This 7th
The relationship between the crack propagation rate {log (da / dN)} and the fluctuation range (log ΔK _eff ) of the effective stress intensity factor shown in the figure is a material constant determined by the material that does not depend on the average stress, and is generally ( It is not necessary to prepare a plurality of data according to the average stress like the relationship of da / dN-ΔK). Further, ΔK _th and ΔK _FC are also built in the memory 42 in advance with the same material constants. And the evaluation result is △
If K _eff ≦ ΔK _th , the propagation of cracks has stopped, there is no further progress, and the machine continues to operate.

Further, within the range of _{ΔK th} ≦ ΔK _eff <ΔK _FC , the current crack propagation speed can be known, and the crack propagation speed in the near future as the remaining life can be approximately obtained, and while continuing the operation. , Determine the repair timing.

Further, if _{ΔK eff} is the region III in FIG. 7, the remaining life is extremely short, the machine must be stopped and repaired promptly, and an operation stop signal will be sent from the operation controller 45, resulting in an emergency stop. In a structure that is impossible to do so, the stress is reduced and the propagation of cracks is slowed down due to the output reduction of the machine while continuing the monitoring.

Such a judgment result is displayed on the display unit 45.

〔The invention's effect〕

Thus, the stress intensity factor measuring gauge of the present invention has a simple structure and can easily measure the stress intensity factor. Further, the stress intensity factor measuring method of the present invention can very easily measure the stress intensity factor based on the output of the gauge for measuring the stress intensity factor, and also nondestructively measures the stress intensity factor with high accuracy. be able to. Further, the residual life monitoring apparatus for a crack member of the present invention can easily measure the effective stress intensity factor in consideration of the opening / closing point of the crack, and also accurately propagates the crack propagation speed, and the crack length in the near future. Since it is possible to estimate and monitor the remaining life, it is possible to prevent unstable breakage of the crack member and to effectively use and maintain the machine.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a stress intensity factor measuring gauge and a crack opening / closing point measuring gauge of the present invention, and FIGS. 2 (a) and 2 (b) are the validity and calibration coefficient of the present invention. A schematic diagram showing the boundary element method analysis target performed for the calculation, FIG. 3 is a characteristic diagram showing the analysis result of the calibration coefficient showing the validity of the present invention, and FIG. 4 (a) (b) (c) are The outline of the test material carried out in order to examine the adequacy of the present invention is shown, the figure (a) is a front view, the figure (b) is a right side view of the figure (a),
The figure (c) is an enlarged view of the gauge part for measuring the stress intensity factor,
FIG. 5 is a block diagram showing an embodiment of the remaining life monitoring apparatus for crack members according to the present invention, and FIG. 6 is a diagram showing a method for determining crack opening / closing points by a gauge for measuring crack opening / closing points, FIG. 7 is a characteristic diagram showing the relationship between crack propagation rate and effective stress intensity factor range, FIG. 8 is a plan view showing a stress intensity factor measuring gauge previously proposed by the present inventor, and FIG. 9 (a). ) (B) is a schematic diagram showing a method of determining a stress intensity factor by a ratio exception insertion method using the gauge of FIG. 21 ... Gauge base, 22 ... 3-axis rosette resistance wire strain gauge, 23 ... Crack, 24 ... Guideline, 2
5 ... Stress intensity factor measuring gauge, 26 ... Key row opening / closing port point measuring gauge, 37 ... Crack member, 38, 40 ... Amplifier, 39 ... Stress intensity factor calculator, 41 ... Opening / closing port Point calculator, 42 ... Memory, 43 ... Evaluator.

Claims (4)

[Claims] 1. When two triaxial resistance wire strain gauges are mounted on a gauge base at intervals and the gauge base is attached in the vicinity of a crack of a crack member, the above-mentioned 2 is formed on the extension line of the crack. A stress intensity factor measuring gauge arranged such that the center of each of the three triaxial resistance strain gauges is located. 2. A guide line comprising a line segment connecting the gauge centers of two triaxial resistance line strain gauges and another guide line orthogonal to the guide line are attached on the gauge base. Gauge for measuring the stress intensity factor according to the first item of the range. 3. Two triaxial resistance wire strain gauges are mounted on a gauge base at intervals, and when the gauge base is attached in the vicinity of the crack of the crack member, the above-mentioned 2 is formed on the extension line of the crack. A stress intensity factor measuring gauge, which is arranged so that the center of each of the three triaxial resistance wire strain gauges is located, is attached in the vicinity of the crack tip of the crack member, and then each of the triaxial resistance wires The stress is detected by the strain gauge, and the following equations (1) and (2) are used based on the detected stress. However, σ _{y | θ = 0} : Tensile stress in the direction orthogonal to the crack propagation direction τ _{xy | θ = 0} : Shear stress r: Distance from the crack tip α _I , α _II : Calibration coefficient T _y : Crack Tensile force when an external force acts on the crack edge T _xy : The shearing force when an external force acts on the crack edge multiplies the detection stress of each triaxial resistance line strain gauge by a calibration factor and applies this to the crack tip. A method for measuring a stress intensity factor, characterized by obtaining a stress intensity factor by extrapolation. 4. Two triaxial resistance wire strain gauges are mounted on a gauge base at intervals, and when the gauge base is attached in the vicinity of a crack of a crack member, the above-mentioned 2 is formed on the extension line of the crack. A stress intensity factor measuring gauge, which is arranged such that the center of each of the three triaxial resistance line strain gauges is located, is attached near the crack tip of the crack member, and then each triaxial resistance line strain is measured. A stress intensity factor calculator that detects the stress with a gauge and calculates the stress intensity factor; and a crack opening / closing point newly attached to the crack edge by the output of the resistance wire strain gauge for measurement. An opening / closing point calculator for calculating the effective stress intensity factor range from this stress intensity factor and the opening / closing point of the crack, and comparing the effective stress intensity factor range with a previously stored material constant. Evaluator for determining the remaining life of Remaining life monitoring system Ruki cleft material.