Pre-existing crack offset three-point bending test device for testing fracture toughness of II type crack

Abstract

The invention provides a pre-existing crack offset three-point bending test device for testing fracture toughness of the II type crack. The device comprises a sample, a lower end clamp, an extensometer, a hammer, and support rollers. Two support rollers are horizontally placed on the lower end clamp and are on the same horizontal plane. The sample is supported on the support rollers, and is a rectangular parallelepiped. The support points of the two support rollers and the sample are symmetrical about the longitudinal central axis and 1.4W from the longitudinal central axis. The bottom surfaceof the sample is provided with two pointed bayonets and V-shaped open slots symmetric about the longitudinal central axis. The distance between the two pointed bayonets is the standard range of the extensometer. The sharp point of the bayonet on the left side is flush with the tip of the corresponding V-shaped open slot, and the tips of the V-shaped open slots are provided with pre-existing cracks. The V-shaped open slots are vertically upward, and are 0.7W from the longitudinal center axis. The pointed bayonets are 1W from the longitudinal center axis. The distance between the pre-existing crack center line and the support rolls on both sides is 1:3. The knife edge of the extensometer is clamped onto the two pointed bayonets. The hammer is placed on the top of the first sample and is inthe same vertical line with the pre-existing crack.

Description

technical field [0001] The invention relates to a test piece for fracture toughness of type II cracks. technical background [0002] Fracture toughness of materials is a basic parameter of fracture mechanics. It is a measure of the ability of materials to prevent the instability of macroscopic cracks from expanding, and it is also a toughness parameter for materials to resist brittle failure. The characteristics are only related to the material itself, heat treatment and processing technology. It is the critical value of the stress intensity factor; it is often expressed by the energy absorbed by the object before fracture or the work done by the outside world on the object. [0003] The basic fracture modes are type I, type II, and type III; type I fracture is also called open mode, which is the most dangerous and most deeply studied fracture mode; type II fracture is also called slip type fracture (slide mode), type III fracture is also called tear type fracture (twist m...

AI Technical Summary

Problems solved by technology

[0004] The direction of the force corresponding to the type I crack is exactly perpendicular to the direction of crack extension, and the direction of the force corresponding to the type II crack is mainly along the direction of the crack surface, that is, the growth of the type II crack is mainly affected by the shear force. Generally speaking, There is no standard test specimen for studying mode II crack growth rate

However, the new prefabricated crack offset three-point bending specimen we designed is prefabricated on the side of the extensometer opening away from the midpoint. Under ideal conditions, the direction of the initial crack is consistent with the direction of the main force. Compared with the principal stress direction, the stress is much smaller than that of the principal stress. If there is a method (similar to the deformation of the flexibility method) that can calculate the crack depth through the extensometer opening displacement, then the type II There will be revolutionary progress in the test method of cracks, and the fatigue growth of type II cracks will be a new subject for research; The prefabricated crack offset three-point bending specimen provides experimental support for the subject of mode II crack fatigue growth

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