A three-point bending specimen device with prefabricated crack offset

Abstract The fracture toughness of a material is a measure of its ability to prevent macroscopic crack instability and propagation. It is the critical value of the stress intensity factor, commonly expressed as the energy absorbed by the object before fracture or the work done by the external environment on the object. The basic fracture modes include Type I, Type II, and Type III. The direction of force corresponding to Type II cracks is mainly along the propagation direction of the crack surface. That is, the propagation of Type II cracks is mainly affected by shear force. Generally speaking, there is no standard sample to study the propagation rate of Type II cracks, and it is impossible to predict and prevent the propagation of Type II cracks accurately. Therefore, it is impossible to measure the fracture toughness of Type II materials accurately, and targeted measures cannot be taken to ensure the structural integrity of materials. This article proposes a new type of prefabricated crack offset three-point bending specimen based on this. The crack is prefabricated on the side far from the midpoint of the extensometer opening. In an ideal state, the initial crack direction is consistent with the main stress direction, and the vertical stress is much smaller than the main stress direction. The crack depth can be calculated by the displacement of the extensometer opening to accurately measure the fracture toughness of the material and provide basic support to ensure the integrity of the material structure.