A unified statistical model for indentation pop-in: Effects of indenter radius and microstructure density on the transition from homogeneous nucleation to heterogeneous nucleation to bulk plasticity
A unified statistical model for indentation pop-in: Effects of indenter radius and microstructure density on the transition from homogeneous nucleation to heterogeneous nucleation to bulk plasticity
复制标题
压痕弹出的统一统计模型：压头半径和微观结构密度对从均匀成核到异质成核再到体塑性转变的影响
DOI：
10.1016/j.ijplas.2021.102980
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发表时间：
2021-03
影响因子：
9.8
通讯作者：
Long Yu
中科院分区：
文献类型：
--
作者：
Xiazi Xiao;Long Yu
压痕突入，即在测量的载荷-穿透深度曲线上突然发生位移突变，被称为晶体材料的弹塑性变形的开始。根据位错成核源的压入半径或密度的不同，弹入剪应力的演化一般可分为三个变形阶段，即均质位错成核阶段、非均相位错成核阶段和体塑性阶段。对于前者，弹入应力的波动主要由热激活成核过程控制。对于中间层，在较大的压头半径和微结构密度范围内，具有应力波动的尺寸相关的弹入行为。对于后者，材料强度由现有位错运动的临界剪切应力决定。在这里，我们发现相邻形变阶段之间的两个额外的转变阶段可以通过一种新的竞争机制有效地解决，并且转变点受位错形核位置密度的影响。本文提出的统一统计模型很好地刻画了所有这些关键特征。在此基础上，建立了非均相位错形核阶段与尺寸相关的突入行为的闭合公式的力学模型。通过用不同的实验数据对标定和预测的理论结果进行比较，得到了很好的一致性，可以合理地验证所提出的模型。这项工作提供了一个描述基本弹入机制的理论框架，并为预测区分不同塑性变形机制的转折点提供了一条途径。
Indentation pop-in, i.e. a sudden displacement burst on the measured load-penetration depth curves, has been known as the onset of elastic-plastic deformation for crystalline materials. Depending on the indenter radius or density of pre-existing dislocation nucleation sources, the evolution of pop-in shear stress can generally be categorized into three deformation stages, i.e. the homogeneous dislocation nucleation stage, heterogeneous dislocation nucleation stage and bulk plasticity stage. For the former, the fluctuation of pop-in stress is dominated by the thermally activated nucleation process. For the middle, a size-dependent pop-in behavior with stress fluctuation is informed over a wide range of indenter radius and microstructure density. For the later, the materials strength is determined by the critical resolved shear stress for the motion of existing dislocations. Here, we find two additional transition stages between the adjacent deformation stages that can be effectively addressed by a novel competition mechanism, and the transition points are affected by the density of dislocation nucleation sites. All these critical features are well characterized by a unified statistical model proposed in this work. Moreover, a mechanistic model with closed-form formulas is developed for the size-dependent pop-in behavior during the heterogeneous dislocation nucleation stage. By comparing both the calibrated and predicted theoretical results with different sets of experimental data, good agreements are achieved that can rationally verify the proposed model. This work presents a theoretical framework to characterize the fundamental pop-in mechanisms, and provides an avenue towards the prediction of transition points distinguishing different plasticity deformation regimes.
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