Sandvik Materials Technology, R&D Center, 81181 Sandviken, Sweden.
Ultrasonics. 2013 Dec;53(8):1406-11. doi: 10.1016/j.ultras.2013.05.008. Epub 2013 May 30.
Fatigue damage behaviors of four metal materials in the very high cycle fatigue (VHCF) regime have been studied using ultrasonic fatigue test and microstructure analysis. The results show that the fatigue crack initiation in VHCF regime could occur at subsurface non-defect fatigue crack origin (SNDFCO), where the accumulated cyclic strains or damage in the specimens were highly localized, especially in the materials with some softer phase, where the local maximum strain can be eight times higher than the average strain value in the specimen. This high strain localization can cause a local plasticity exhaustion that leads to a stress concentration and consequently fatigue crack initiation, and finally the formation of SNDFCO. For pure single phase austenitic material, strain localization can also occur due to dislocation accumulation at or near grain boundaries, which can become fatigue crack initiation origin in the VHCF regime. The results in this study show that fatigue damage and crack initiation mechanisms in the VHCF regime can be different in different metals due to the mechanisms for local plasticity exhaustion.
采用超声疲劳试验和微观结构分析研究了四种金属材料在超高周疲劳（VHCF）区的疲劳损伤行为。结果表明，VHCF 区的疲劳裂纹萌生可在亚表面无缺陷疲劳裂纹起源（SNDFCO）处发生，在试样中，循环应变或损伤累积高度集中，特别是在具有某些较软相的材料中，局部最大应变可比试样中的平均应变值高 8 倍。这种高应变集中会导致局部塑性疲劳，从而导致应力集中，最终导致疲劳裂纹萌生和 SNDFCO 的形成。对于纯单相奥氏体材料，由于位错在晶界处或附近堆积，也会发生应变集中，从而在 VHCF 区成为疲劳裂纹萌生的起源。本研究结果表明，由于局部塑性疲劳的机理不同，不同金属在 VHCF 区的疲劳损伤和裂纹萌生机理可能不同。
