等軸α/針状α混合組織Ti-6Al-4V合金の一定振幅荷重および非定常変動荷重下における疲労き裂進展挙動

概要

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Fatigue crack growth behavior under constant and non-stationary variable amplitude load sequences was investigated using compact tension specimens of Ti-6Al-4V alloy with bimodal microstructure. Fatigue crack growth rate and macroscopic crack closure were measured by means of an unloading elastic compliance method. The da/dn-⊿K_<eff> relationship under constant amplitude exhibited a trilinear form even in so-called Paris region corresponding to the change of growth mechanism from the intergranular fracture in the low ⊿K region to the transgranular one in the high ⊿K region. The fatigue crack growth rate under two-step block loading was found to be higher than that estimated by da/dn-⊿K_<eff> relation under constant amplitude loading, indicating that the load variation resulted in the crack growth acceleration terms of ⊿K_<eff>. The load variation induced the transgranular fracture in the low level loading where the intergranular fracture type was dominant under constant amplitude loading. It is considered that the transition of fracture type in the low level loading resulted in the acceleration. Under single over loading, however, the crack growth deceleration in terms of ⊿K_<eff> was observed due to the blunted crack tip.
一般社団法人日本機械学会の論文
2005-08-25