JPS5988641A - Rapid evaluation of crack development speed - Google Patents

Abstract

PURPOSE:To rapidly estimate a crack development speed with good accuracy under an optically and directly non-observable environmental condition such as the interior of an autoclave, by measuring load and a change curve with the elapse of time in the displacement of a loading point. CONSTITUTION:A crack speed is shown by a formula wherein (a) is a crack length, P is load, V is the displacement of a loading point, B is the thickness of a test piece, E is young modulas and K is coefficient of stress enlargement. Because K is an amount uniquely determined by (a), P, the crack speed can be analyzed theoretically. Load is applied to the breaking dynamics type test piece at a definite low tensile speed by a tensile testing machine and load P and the displacement V of the loading point are measured by a load meter and a displacement meter to be inputted to a computer while subjected to AD conversion while the time differentiation curves of the load P and the displacement V are fabricated. Succeedingly, a program for calculating coefficient K of stress enlargement is used to successively calculate a crack development speed, a crack development amount and the coefficient K of stress enlargement and the relation of the coefficient of stress enlargement and the crack development speed is calculated to be drawn by an XY-plotter.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] [Technical Background of the Invention and Problems Therewith] The amount or speed of a T-crack growth test using a fracture mechanics type specimen is determined by the stress intensity factor, which is a fracture mechanics parameter. Alternatively, it is an evaluation method of material strength described in terms of J-integral value, etc., but the present invention is intended to apply this method to structures such as nuclear reactors, etc., and to provide crack propagation as in an autoclave.

Basically, the only information that can be used is the time-course curve of load and load point displacement, and b deviation is also a basic quantity in mechanical strength testing of materials and is easy to measure. That is, using the load P and the load point displacement ■, the compliance λ is defined as λ=■/P. By differentiating both sides with respect to time t, the following equation is obtained.

dλ dV dP TV= ””iu” ”Ti:” )/”'
(1) dλ dλ da dt da −; IU f
2) means the rate of change in compliance, which can generally be calculated for fracture mechanics type test specimens, and is expressed by the following formula in the case of CT test specimens, for example.

μshi(2B, ni2)/(B-P”) (3
1a where B is the specimen thickness, E is Young's modulus, and K is the stress intensity factor. The above appears in the second factor on the right side of equation (2))
It can be organized using the following formula for crack velocity.

d a d 'V d P week〒
=E・(■・P-V-il-T-)/(2J3・K')
+41 In equation (4), the time derivatives of P and V change over time. Fig. 1 shows a flowchart of an example of application of this method in 5RLT using a CT test piece. Try it first.

The principle of this technology and the procedure for an 8-box LT using CT test pieces have been described above, but by configuring this technology as an automatic processing system using a computer, it is possible to speed up data processing and save labor.

Next, an example of the system configuration is shown in FIG. 2. The configuration includes a load cell attached to the tensile testing machine, a displacement meter, an X-t recorder, and an A/D on the data analysis side! converter, calculation ffl, time tt
, an X-Y plotter, and a cassette recorder.

Next, the functions of this system will be explained. A fracture mechanics type test piece set in a tensile testing machine is loaded at a constant low tensile rate. At this time, the load and load point displacement are measured by a load cell, respectively.
These two pieces of analog data are continuously measured by a displacement meter, and these two pieces of analog data are plotted on an X-t recorder for monitoring as a time-dependent change curve of load and load point displacement.

Another flow is to convert these two data to A/D.
input into the converter, after A/11 conversion, call it into the computer, and according to the procedure already described, calculate the time differential curve of the load,
Create a time differential curve of displacement and find its relationship. These results are plotted on an X-'Y plotter and at the same time are cassetted as data.

[Embodiments of the invention]

Next, an example will be shown in which auste motion was analyzed using a system using the present invention. The test piece has a crack growth rate K = 60 kgf 7 mm, calculated from 0.8 inches.
and 100kgf//+1+++37'' are shown in Table 1 in comparison with the speed determined by SU8 by the system using the present invention (with the exception of -60kgf
/mm” and 100 kgf/mm3=) shows good agreement, and at the same time, when determined from the fracture surface of the test piece, the average value over the entire test time can be obtained with the highest accuracy and reproducibility. I understand.

〔Effect of the invention〕

As explained above, according to the crack growth rate evaluation method according to the present invention, it is possible to accurately determine the crack growth rate in an autoclave. Further, by configuring an automatic processing system using a computer, it becomes possible to further speed up data processing and save labor.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the procedure when this method is applied to S-LT using CT specimens, and Figure 2 shows an example of the case configured as an automatic processing system using a computer. It is a block diagram.

Claims (1)

[Scope of Claims] (1) In the case of a load, the time derivative of the load and the load point displacement (each Find the change over time of dP dV , a-",-aT), and da
dV dP=F"C4' L-a
−T)/(2i+−K”)(t t d
t