Anomalous tension-compression asymmetry in amorphous silicon: insights from atomistic simulations and elastoplastic constitutive modeling

B Ding and L Hu and Y Gao and YL Chen and XY Li, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, 186, 105575 (2024).

DOI: 10.1016/j.jmps.2024.105575

Recent experiments observed an inherent, anomalous tension-compression (T-C) asymmetry with T>C in microscale amorphous silicon (a-Si), which is free of dominant microcracks or dislocations. However, quantifying the disordered structure of a-Si and correlating it with T-C asymmetry remains mysterious. Here, we first conduct a series of atomistic simulations to explore this anomaly in a-Si. Results reveal a positive correlation between cooling rate q and fraction of liquid-like phase phi(ll), suggesting that higher cooling rates trap more atoms in liquid- like phase. Uniaxial tension and compression tests reveal that T-C asymmetry with T>C persists across all cooling rates, where the physical origin is attributed to variations in initial phi(ll) and its subsequent spatial and temporal evolutions during loading. A physics based, Mohr- Coloumb type elastoplastic constitutive model, determining cohesion c by the content of liquid-like component phi(ll), successfully reproduces the observed anomalous T-C asymmetry and its dependence on the initial structure in a-Si. Furthermore, the degree of asymmetry tends to diminish with an increase in initial phi(ll), a trend general to both amorphous Si and CuZr metallic glass (MG). While the contrasting atomic volumes of the liquid-like phase in a-Si and MG explain their differing T-C asymmetries, with a-Si exhibiting T>C and CuZr exhibiting T

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