Microscopic Stress/Strain Field around a Crack Tip and Fracture Process in WC-Co Composite

Abstract

On two-phase materials, there exists a microscopic stress/strain field resulting from their microstructure as well as a macroscopic stress/strain field in the region near a crack tip. The fracture behavior of such materials seems to depend strongly on the microscopic stress/strain field. In this paper, the analysis of the microscopic stress/strain field around a crack tip in WC-Co composites, whose Co-volume fractions are 10 %, 30 % and 50 %, has been carried out by the finite element method based on a mechanical model of two-phase sintered materials proposed in a previous paper. In the region ahead of a crack tip, the microscopic stress on WC-grain and the microscopic strain on the Co-phase are larger than the macroscopic stress or strain, respectively. The microscopic stress on WC-grain increases with an increase in Co-volume fraction. From the comparison of the numerical results with the experimental results of fracture toughness in reference, it is suggested that microcracking occurs on the WC-grain ahead of a crack tip before final fracture, and that the process from the microcracking to the final fracture is the toughening mechanism due to ductile fracture of the Co-phase.