JP2596082B2 - J ▲ Lower 1 ▼ Lower c ▼ Test method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an elasto-plastic toughness test (so-called _J1C test) which is positioned as one of the fracture safety evaluation methods using nonlinear fracture mechanics. On data processing to determine compliance in this _J1C exam.

B. Prior Art In a _J1C test, as shown in FIG. 2, while applying a tensile load P to a test piece S _J subjected to fatigue pre-cracking, the magnitude of the load P is measured by a load detector 4 ( for example, measured by the load cell), and amplifies the detection signal by the load amplifier DA _4, to obtain a load measurement signal. On the other hand, a displacement V _L (hereinafter, referred to as a load point displacement) on the load line is measured by a displacement detector 5 (for example, a clip gauge) inserted and installed at the edge of the notch portion 1 _J , and the detection signal is transmitted to a displacement amplifier DA.
It is amplified by ₅ to obtain the displacement measurement signal. Then, slightly respectively, in multiple levels of load point displacement V _L (e.g., about 10%) divided by the load, the measurement result representing a third relationship between the load P- load point displacement V _L as shown in the figure, and , And a measurement result obtained by amplifying the unloading portion as shown in FIG.

From this measurement result, the load P at each unloading point,.
-Compliance λ which is the slope of the load point displacement _VL curve
(Λ = ΔV _L / ΔP: ΔP is a change amount of the load P at the time of unloading, and ΔV _L is a change amount of the load point displacement _{VL due to} the change), and energy A (load P , And the integrated values up to,...), And based on the calculation results of the compliance λ and the energy A, the J integrated value and the amount of crack growth at each unloading point,. A curve called a JR curve indicating the relationship with the tension limit J integral value J is obtained from the JR curve.
_1C has been determined.

By the way, the compliance λ at each of the unloading points,... Is based on the expanded data of [load (P), load point displacement (V _L )] as shown in FIG. When the unloading points are further enlarged and viewed in detail, as shown in the schematic diagram of FIG. 5, first, the increase in the tensile load P is stopped (stop point H),
After being instantaneously held (holding portion I: an increase in the load point displacement _VL is also observed during this period), unloading is started (unloading start point J _S ), and then the tensile load P is reduced to the stop point. H
The load is gradually unloaded until the load P decreases by about 10%, and the unloading operation ends (the unloading end point J _e ).

At this time, as is clear from FIG. 5, the unloading start point J _S
Between reaching the unloading end point J _e from the data of [the load (P), the load point displacement (V _L)] is not in a straight line, both ends (i.e., immediately after the unloading start point J _S and Just before the unloading end point J _e )
, There is a tendency that a swelling portion (in other words, an overshoot portion of the load point displacement _VL ) K is generated immediately after the unloading start point _JS .

Therefore, conventionally, in order to obtain the compliance λ as accurately as possible, both ends of the sampling data of [load (P), load point displacement (V _L )] as shown in FIG. A data processing method is used in which a fixed number of data in each part is cut, and only linear sampling data in the middle part is adopted as data for calculating compliance λ (generally, the data is calculated by the least square method). .

C. Problems to be Solved by the Invention However, such a conventional method has the following problems.

That is, the degree (size and length) of the bulging portion K generated immediately after the unloading start point _JS described with reference to FIG. 6 actually differs at each unloading point,. If the data processing of simply cutting a certain number of data at both ends of the sampling data of [load (P), load point displacement (V _L )] is applied as in the method, If K is relatively large, it cannot be completely removed and the linearity of the remaining data will be poor, or a large number of data will be transiently discarded because the bulge is relatively small. Inevitably, the number of data in the necessary straight line portion is unexpectedly reduced, and in any case, the accuracy of calculating the compliance λ deteriorates. That.

The present invention has been made in view of such circumstances, and a non-linear portion at both ends of sampling data of [load, load point displacement] for compliance calculation is appropriately truncated to calculate compliance. accuracy, that is, an object of the invention to provide a J _1C test method can improve the accuracy of the J _1C test.

D. Means for Solving the Problems The present invention has the following configuration to achieve the above object.

That is, according to the present invention, a tensile load is applied to a test subjected to fatigue pre-cracking, the load is slightly unloaded at a plurality of levels of the load point displacement, and the slope of the load-load point displacement curve at each unloading ( Compliance), and in the _J1C test method for determining the tensile limit J integral value ( _J1C value) based on the compliance, sampling data of load-load point displacement from the start point to the end point of the unloading. Of the load point displacement between the load point displacement at the unloading start point and the load point displacement at the unloading end point, and belonging to the range of the load point displacement obtained by cutting a predetermined percentage of both ends thereof. The compliance is determined from the sampling data.

E. Operation Generally, the load point displacement corresponding to the bulge immediately after the unloading start point has a larger value than the load point displacement at the unloading start point. However, according to the present invention, at least the data between the load point displacement at the unloading start point and the load point displacement at the unloading end point, and the range of the load point displacement obtained by cutting a predetermined percentage of both ends thereof Since the sampling data of the load-load point displacement belonging to the above is adopted as the data for calculating the compliance, the data of the bulging portion having a value larger than the load point displacement at the unloading start point is unconditionally cut. In other words, irrespective of the size of the bulge portion, the data of that portion is cut, and the compliance is calculated with high accuracy.

F. Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

The first figure shows the sampling data to be collected during the unloading start point J _S until the unloading end point J _e [load (P), the load point displacement (V _L)].

As shown in the figure, the load (P) and the load point displacement (V _L ) from the unloading start point J _S [P _S , V _LS ] to the unloading end point J _e [P _e , V _Le ] are shown. )], The data used for the compliance calculation is at least between the load point displacement V _LS at the unloading start point J _S and the load point displacement V _Le at the unloading end point J _e (in the figure, A region). In other words, the load point displacement V _LS of the unloading start point J _S
The data in the area B in the figure having a larger value is the data of the bulge immediately after the unloading start point _JS , and these data are cut without affecting the degree of the bulge.

Further, when the number of sampling data in the area A is 100%, the end data of Δv _S % on the unloading start point side and the end data of Δv _e % on the unload end point side are respectively obtained. By cutting and adopting the sampling data of the C region in the figure as compliance calculation data, the compliance calculation accuracy is further improved.

After all, the range of the load point displacement V _L sampling data corresponding to the C region is used as a compliance _{calculation, V Le + (V LS -V} Le) · Δv e / 100 ≦ V L ≦ V LS - (V _LS −V _Le ) · Δv _S / 100. In this embodiment, Δv _S (%), Δv
_e The value of (%) is set to 5%. However, these ratios may be either the same value or different values, and the numerical values are not particularly limited. However, since the data of the bulge portion (B region) is cut as described above, Sufficient measurement accuracy can be obtained with extremely small numerical values.

G. Effects of the Invention As is clear from the above description, J _{1C according} to the present invention
According to the test method, simply [load,
Instead of cutting a fixed number of data at both ends of the sampling data of the load point displacement), between the load point displacement at the unloading start point and the load point displacement at the unloading end point, and It belongs to the range of the load point displacement that cuts a predetermined ratio of both ends [load, load point displacement]
Is adopted as the data for calculating the compliance, so that the bulge generated immediately after the start of unloading, which has been a particular problem in the past, can be reliably cut regardless of its size. . Further, by this, the number of data to be cut by the predetermined ratio can be set relatively small, so that the data for compliance calculation does not unexpectedly decrease, and the calculation accuracy of the compliance, and thus J _1C The accuracy of the test can be greatly improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of sampling data used for compliance calculation in the _J1C test method according to one embodiment of the present invention. 2 to 6 relate to a description of a conventional _J1C test method, FIG. 2 is a block diagram of a main part of a _J1C test apparatus, FIG. 3 is a characteristic diagram showing a load-load point displacement relationship, FIG. 4 shows the third
Enlarged characteristic diagram of the unloading section of the figure, FIG. 5 is a schematic diagram showing from the stopping point in J _1C test to unload end point, FIG. 6 is used for compliance calculated in a conventional J _1C Test method FIG. 4 is an explanatory diagram of sampling data. S _J … Test piece, P… Tensile load _VL … Load point displacement,…… Unloading point J _S …… Unloading start point, J _e …… Unloading end point

Claims (1)

(57) [Claims] 1. A tensile load is applied to a test piece subjected to fatigue pre-cracking, and the load is slightly unloaded at a plurality of levels of load point displacement. Compliance), and the tensile limit J integral value ( _J1C value) is calculated based on the compliance.
_{In the 1C} test method, among the load-load point displacement sampling data from the load unloading start point to the load unloading point, the load-point displacement at the load unloading start point and the load point displacement at the load unloading end point. A _J1C test method, wherein the compliance is obtained from load-load point displacement sampling data belonging to a load-point displacement range obtained by cutting a predetermined ratio at both ends thereof.