A Method for Measuring the Threshold Value of Stress Intensity Factor of Mode II Crack in Metallic Materials

Abstract

The invention discloses a method for measuring the threshold value of stress intensity factor of type II cracks in metal materials. The left end of the sample is fixed by a sample fixing mechanism, the right end is provided with a horizontal gap extending from the right end to the center, and the inner end of the gap is provided with a tip facing the right end The triangular crack initiation and expansion part of the surface, and the vertical edge at the tip is provided with a V-shaped notch, and a support rod is inserted into the gap; between the upper clamping part and the upper cantilever of the clamping mechanism package and the lower clamping part and There are stress conducting rods between the lower cantilevers. The fatigue testing machine applies a reciprocating load through the upper cylinder on the upper part of the upper clamping part. After the test, cut the sample perpendicular to the end face, observe the type II crack, and calculate the type II The magnitude of the stress intensity factor corresponding to the critical length of the crack is the threshold value of the stress intensity factor for the type II crack of the metal material. The invention is beneficial to ensure the initiation of cracks on the neutral plane, to ensure that the shear stress decreases with the increase of the crack length, and to ensure the stable expansion of the cracks along the neutral plane of the sample.

Description

technical field

[0001] The invention relates to the technical field of metal material crack detection, in particular to a method for measuring the threshold value of the stress intensity factor of a metal material type II crack. Background technique

[0002] At present, there is no standard test method and type test equipment for testing the threshold value of the stress intensity factor of the metal material type II crack. The current test standards (such as the national standard GB-T6398 metal material fatigue crack growth rate test method) are only applicable to type I cracks, and fatigue testing machine manufacturers only provide stereotyped equipment for measuring the threshold value of the stress intensity factor of type I cracks.

[0003] figure 1 It is the schematic diagram of the type II crack growth test, and the sample adopts a double cantilever beam structure. Under the action of the cyclic load P shown in the figure, the normal stress on the sample is σ x a...

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