Fatigue Crack Initiation and Propagation at a Sharp Notch in Zr-based Bulk Metallic Glass

摘要

Fatigue strength of notched specimen and smooth specimen of Zr-based bulk metallic glass, Zr_(55)Cu_(30)Ni_5Al_(10), were conducted under either plane-bending or axial-loading. Fatigue notch factor, K_f, for axial-loading was almost equal to the elastic stress concentration factor, K_t, and the value of K_f for plane-bending was 5% lower than the value of K_t. It indicates that the effect of stress gradient around notch root is negligible, and the fatigue limit of notched specimen is determined by the stress at the notch root. On the contrary, the fatigue strength and the fatigue limit were lower for axial-loading than plane-bending either for notched or smooth specimen. It is considered that the fatigue strength of BMG depends on the cooling rate in the casting process of the material, which is different along the thickness direction, and the fatigue strength of plane-bending reflects the strength at the specimen surface while that of axial-loading is determined by the weakest strength in the thickness direction.