Fracture and Fatigue of Polycrystalline-Diamond Compacts

Abstract

Summary Four different batches of polycrystalline-diamond compacts (PDCs) were tested under monotonic and cyclic loadings. Initially, the mean load to fracture was recorded for each batch. In fatigue tests, the specimens were preloaded to between 75 and 95% of a batch mean static (S) strength and the R-ratio of 0.1 was used with frequencies of 10 and 20 Hz. It was found that some PDCs sustained greater than 106 cycles without fracturing. It was also noted that fracture force was reduced by 10 to 35% after the specimens were subjected to cyclic loading. This could indicate that fatigue weakens the structure of the PDC material. Tests conducted on two opposing edges of the same PDC buttons showed that the fracture on one side does not affect the strength of the opposing side. Thus, PDCs whose fracture or wear on flat areas is relatively small can be salvaged from the old bits, rotated 180°, and then rebrazed. Investigation of the fracture surface using a scanning-electron microscope (SEM) revealed that the fracture followed a transgranular path.