Ｔｉ‐６Ａｌ‐４Ｖ合金における単一過大荷重下の低サイクル疲労き裂進展特性

Abstract

In this study, the low cycle fatigue deformation properties and the surface crack propagation behaviour of α/β-rolled plates of Ti-6Al-4V alloy with conventionally annealed equiaxial microstructure were investigated under the constant strain amplitude and the single over-straining conditions. Two types of the single over-straining were performed; that is, tension only (T waveform) and tension-compression (T-C waveform) over-straining, and the effects of the overstraining ratio λ on the cyclic deformation and the crack acceleration or the crack retardation behavior were also studied from the stand-point of the changes in crack opening displacement Φ and tensile peak stress σpt. As the results, in the T waveform test in the range of λ≥1.62, the crack ratardation occurred when compared with the crack propagation of the constant amplitude test, and the retardation effect increased with the ratio λ. On the other hand, in the T-C waveform test, the crack propagation curve after over-straining was almost coincident with the curve of the constant amplitude test. It became clear that the retardation behaviour of surface crack propagation after the over-straing of the T waveform resulted from both of the changes in Φ and σpt after the over-straining. The relation between the crack propagation rate da/dN and the J integral range ΔJ under the over-straining conditions was in good agreement with the da/dN and ΔJ relation of the constant strain amplitude test.