Atomistic prediction of the temperature- and loading-rate-dependent first pop-in load in nanoindentation
Atomistic prediction of the temperature- and loading-rate-dependent first pop-in load in nanoindentation
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DOI：
10.1016/j.ijplas.2019.06.012
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发表时间：
2019-10
影响因子：
9.8
通讯作者：
Yuji Sato;Shuhei Shinzato;T. Ohmura;S. Ogata
中科院分区：
文献类型：
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作者：
Yuji Sato;Shuhei Shinzato;T. Ohmura;S. Ogata
纳米压痕技术用于材料力学性能的研究已有很长的历史。一个众所周知的位移突发，所谓的“弹出”，通常是观察到在纳米压痕测试。特别是对于第一弹出已经得到了很好的研究，因为它应该直接关系到压头下的局部体积的基本机械强度。对于无缺陷的局部体积测得的第一弹出载荷对应于均匀位错成核的起始载荷，而对于具有固定缺陷的局部体积测得的是异质位错成核的起始载荷。第一次弹出是在加载下的热激活事件;因此，弹出负载表现出温度和加载速率依赖性。虽然理论研究已经成功地解释了温度和加载速率的依赖关系，据我们所知，原子预测的具体材料，考虑到压力状态下的压头尚未报告。在这项研究中，我们提出了一个原子通知多尺度（两个尺度）建模预测的温度和加载速率的依赖关系的第一弹出负载考虑原子估计的应力状态下的压头和应力相关的激活能的位错成核的均匀位错成核。选择体心立方Fe和Ta作为目标金属，尽管该方法通常适用于任何韧性材料。除了均匀位错成核，我们还开发了一个异质成核理论来解释实验和原子获得的均匀成核弹出负载之间的差异。
Nanoindentation has been used for a long time to investigate the mechanical properties of materials. A well-known displacement burst, the so-called “pop-in,” is usually observed during nanoindentation tests. In particular for the first pop-in has been well studied because it should be directly related to the fundamental mechanical strength of the local volume beneath the indenter. The first pop-in load measured for a defect-free local volume is corresponding to the onset load of homogeneous dislocation nucleation, while measured for a local volume with immobile defects is that of heterogeneous dislocation nucleation. The first pop-in is a thermally activated event under loading; thus, the pop-in load exhibits both temperature and loading-rate dependencies. Although theoretical studies have successfully explained the temperature and loading-rate dependencies, to the best of our knowledge, an atomistic prediction for specific materials which takes into account the stress state beneath the indenter has not yet been reported. In this study, we propose an atomistically informed multiscale (two-scale) modeling to predict the temperature and loading-rate dependencies of the first pop-in load for the homogeneous dislocation nucleation considering an atomistically estimated stress state beneath the indenter and stress-dependent activation energies of dislocation nucleation. Body-centered-cubic Fe and Ta are chosen as target metals, although the method is generally applicable to any ductile material. In addition to the homogeneous dislocation nucleation, we also developed a heterogeneous nucleation theory to explain the difference between the experimentally and atomistically obtained homogeneous nucleation pop-in loads.