Author(s)

S. Doi & M. Yasuoka

Abstract

Rotating bending fatigue test was carried out using the cemented carbide WC-Co in ultra-long life. A carbide metal WC has many defects on the boundary. A crack initiates from these defects, and propagates belong the boundary. Fatigue limit does not exist. The boundary slips easily, and is weak to sharing force. The fatigue crack propagation rate (da/dN) cannot calculate. But, fracture toughness KIC can calculate from relationship fractal dimension or Hurst number (localized wavelets transformation) and yield area. Yield area of fracture in ultralong Nf=2.05×107 broad Origin of fracture is surface defects. When KIC>Kmax in surface stands up, the crack in the plane stress propagate. The fatigue strength of WC cemented carbide is obeyed to weakest link model of defects. Because, even if it supposes that it was worked the cyclic stress over the fatigue strength, the fatigue fracture did not always happen. If Kmax/KIC=const. stands up, a small crack is equivalent to a small defect, and fracture of material is induced by initiated crack. By the fractal dimension analysis, the phenomenon of fracture mechanisms will be clear. Keywords: fracture toughness, cemented carbide WC, double bending S-N curve, fractal dimension, Hurst number.

Keywords

fracture toughness, cemented carbide WC, double bending S-N curve, fractal dimension, Hurst number