Scale-dependent pop-ins in nanoindentation and scale-free plastic fluctuations in microcompression
Scale-dependent pop-ins in nanoindentation and scale-free plastic fluctuations in microcompression
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DOI：
10.1557/jmr.2019.386
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发表时间：
2020-01
影响因子：
2.7
通讯作者：
John Shimanek;Q. Rizzardi;G. Sparks;P. Derlet;R. Maaß
中科院分区：
文献类型：
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作者：
John Shimanek;Q. Rizzardi;G. Sparks;P. Derlet;R. Maaß
纳米压痕和微晶变形是两种可以探测晶体塑性尺寸效应的方法。在许多微晶变形的情况下，塑性流动过程中事件大小的无标度和潜在普遍的间歇性已被揭示，而纳米压痕主要用于评估第一次弹出的应力统计数据。在这里，我们证明两种变形方法表现出从塑性不稳定性中获得的根本不同的事件大小统计数据。纳米压痕导致尺度依赖性间歇性微塑性，最好通过威布尔统计（第一次弹出的应力和大小）和对数正态统计（高阶弹出的大小）来描述。相比之下，即使在探测与纳米压痕中相同的塑性体积时，相同材料的有限体积微晶变形也表现出截断幂律类型的微塑性事件尺寸间歇性。此外，我们成功测试了先前提出的极值统计模型，该模型将平均第一临界应力与基础威布尔分布的形状和尺度参数相关联。
Nanoindentation and microcrystal deformation are two methods that allow probing size effects in crystal plasticity. In many cases of microcrystal deformation, scale-free and potentially universal intermittency of event sizes during plastic flow has been revealed, whereas nanoindentation has been mainly used to assess the stress statistics of the first pop-in. Here, we show that both methods of deformation exhibit fundamentally different event-size statistics obtained from plastic instabilities. Nanoindentation results in scale-dependent intermittent microplasticity best described by Weibull statistics (stress and magnitude of the first pop-in) and lognormal statistics (magnitude of higher-order pop-ins). In contrast, finite-volume microcrystal deformation of the same material exhibits microplastic event-size intermittency of truncated power-law type even when the same plastic volume as in nanoindentation is probed. Furthermore, we successfully test a previously proposed extreme-value statistics model that relates the average first critical stress to the shape and scale parameter of the underlying Weibull distribution.