Determination of the fracture properties of metallic materials using pre-cracked small punch tests

摘要

In this paper, the use of pre-cracked small punch test (p-SPT) miniature specimens to obtain the fracture parameters of a material is presented. The geometry of the specimens used was square of 10 × 10 mm with a thickness of 0.5 mm. An initial crack-like notch was created in the SPT specimens by means of a laser micro-cutting technique. In order to obtain the fracture parameters from p-SPT specimens three different approaches have been considered here. The first approach is based on the crack tip opening displacement concept, the second is based on the measure of the fracture energy using the area under the load-displacement curve for different crack sizes, and the third approach is based on the direct numerical simulation of the p-SPT specimen and the numerical calculation of the J-integral. In order to study the crack initiation in these p-SPT specimens, several interrupted tests and the subsequent scanning electron microscope analysis have been carried out. The results indicate that p-SPT specimens can be used as an alternative method for determining the fracture properties of a material in those cases where there is not enough material to undertake conventional fracture tests. For these p-SPT specimens, the multi-specimen method for the determination of the fracture energy is the most promising approach. The results indicate that this small specimen size allows the value of the material toughness, under low constraint conditions to be obtained.