ESSENTIAL CHARACTERISTICS AND INFLUENTIAL FACTORS FOR VERY-HIGH-CYCLE FATIGUE BEHAVIOR OF METALLIC MATERIALS

The research on very-high-cycle fatigue (VHCF) of metallic materials has become a new horizon in the field of metal research since 1980s. The behaviors of crack initiation and propagation, and the characteristics of S-N curve for metallic materials in the VHCF regime all differ from those in the low cycle and high cycle fatigue regimes. For VHCF, the cyclic stress is below the level of conventional fatigue limit and the crack initiation tends to shift from surface to interior. The defects of material, including inclusions, grain-boundary, phase interface and other micro-inhomogeneities may become interior crack initiation site. The S-N curve containing VHCF regime may present "duplex" or "step-wise" shape. The behaviors of VHCF for metallic materials are substantially affected by the strength of material, loading frequency, loading environment, etc. This paper attempts to review the research progress of essential characteristics and influential factors for VHCF behavior of metallic materials. In addition, the aspects for further research on VHCF of metallic materials are proposed, which are the process and mechanism of fatigue crack initiation and early growth, the effects of loading frequency and the environment on VHCF property, and development of quantitative model for VHCF.