International Center for Applied Mechanics, State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University , Xi'an 710049, China.
Department of Engineering Mechanics, Zhejiang University , Hangzhou 310027, China.
Nano Lett. 2015 Oct 14;15(10):7010-5. doi: 10.1021/acs.nanolett.5b03045. Epub 2015 Oct 5.
Despite the utmost importance and decades of experimental studies on fatigue in metallic glasses (MGs), there has been so far little or no atomic-level understanding of the mechanisms involved. Here we perform molecular dynamics simulations of tension-compression fatigue in Cu50Zr50 MGs under strain-controlled cyclic loading. It is shown that the shear band (SB) initiation under cyclic loading is distinctly different from that under monotonic loading. Under cyclic loading, SB initiation takes place when aggregates of shear transformation zones (STZs) accumulating at the MG surface reach a critical size comparable to the SB width, and the accumulation of STZs follows a power law with rate depending on the applied strain. It is further shown that almost the entire fatigue life of nanoscale MGs under low cycle fatigue is spent in the SB-initiation stage, similar to that of crystalline materials. Furthermore, a qualitative investigation of the effect of cycling frequency on the fatigue behavior of MGs suggests that higher cycling frequency leads to more cycles to failure. The present study sheds light on the fundamental fatigue mechanisms of MGs that could be useful in developing strategies for their engineering applications.
尽管金属玻璃（MGs）的疲劳问题具有至关重要的意义，并且已经开展了数十年的实验研究，但迄今为止，人们对其中涉及的机制仍知之甚少，几乎没有原子层面的理解。在这里，我们在应变控制循环加载下对 Cu50Zr50MGs 的拉伸-压缩疲劳进行了分子动力学模拟。结果表明，循环加载下的剪切带（SB）起始与单调加载下的起始明显不同。在循环加载下，当在 MG 表面累积的剪切变形区（STZ）聚集体达到与 SB 宽度相当的临界尺寸时，SB 开始出现，并且 STZ 的累积遵循幂律关系，其速率取决于施加的应变。进一步表明，纳米级 MGs 在低周疲劳下的几乎整个疲劳寿命都花费在 SB 起始阶段，这与晶态材料相似。此外，对循环频率对 MGs 疲劳行为的影响进行的定性研究表明，较高的循环频率会导致更多的失效循环。本研究揭示了 MGs 的基本疲劳机制，这对于开发其工程应用策略可能是有用的。
