抄録
Crack propagation tests of lead-free solder were conducted using center-notched plates under load-controlled conditions. The loading waveform was triangular with fast loading and fast unloading (pp waveform), and trapezoidal with hold time under tension and compression (cc-h waveform). Creep J-integral, ΔJ_c, and fatigue J-integral, ΔJ_f, estimated from load-displacement relations were used to correlate the crack propagation rate. The crack propagation rate, da/dN, was cycle-dependent at high frequency and gradually became time-dependent with decreasing frequency. The transition of da/dN from cycle to time dependence is the region of creep-fatigue interaction. This creep-fatigue interaction was mainly caused by creep deformation was enhanced by cyclic plastic deformation. The relation between da/dN and ΔJ_f for fatigue growth and that between da/dN and ΔJ_c, for creep growth are rather independent without interaction. The striation spacing found on fracture surfaces was nearly equal to the crack propagation rate. A model of the formation of striation formation under creep-fatigue interaction was proposed.
