玻璃态聚合物纳米压痕的单轴恢复视角
Uniaxial Recovery Perspective of Glassy Polymer Nanoindentation
AI总结：
本文将玻璃态聚合物纳米压痕恢复与单轴压缩行为关联，提出屈服归一化恢复曲线和广义幂律模型，揭示等效应变、相关系数及压头下应变分布的早期共性。
摘要：
玻璃态聚合物的尖压头纳米压痕是一种受约束的、局部化的黏弹塑性变形。我们以已被充分理解的单轴变形来解释这种复杂性。基于文献中PMMA、PC和交联SU-8的单轴压缩数据，我们获得了它们通用的、经屈服归一化的恢复曲线，其中eps*=eps/eps_y是相应应变状态（CSS）的一种度量。纳米压痕恢复由2秒恒速率卸载h-P数据确定，并采用广义幂律（可变幂指数）建模。比较这些数据集可得到名义纳米压痕应变率epsdot_N与应变以及真应变率和应变之间的相关系数，即c=epsdot_N/epsdot_t=eps_N/eps_t。从压痕开始起，任何聚合物的等效应变eps和c值都处于一个狭窄范围内。将扫描探针显微术得到的残余轮廓与压头尖端的数学建模相结合，可给出尖端下方的应变分布。本文考察的CSS度量表明，存在从聚合物特有区域到玻璃态聚合物共有区域的变化，而这些区域在纳米压痕的极早期即已达到。
英文摘要：
Sharp tip nanoindentation of glassy polymers is a constrained, localized viscoelastoplastic deformation. We interpret this complexity, in terms of the well-understood uniaxial deformation. From the uniaxial compression data in the literature, for PMMA, PC and crosslinked SU-8, we obtain their universal, yield-normalized recovery curves, with eps*=eps/eps_y, being one measure of the corresponding strain states (CSS). Nanoindentation recovery is determined from the 2sec constant rate unloading h-P data, modeled by a generalized power-law (variable power exponent). Comparing these data-sets, yields the correlation coefficient between the notional nanoindentation strain rate epsdot_N and strain and true strain rate and strain, c=epsdot_N/epsdot_t=eps_N/eps_t. The equivalent strain, eps, and the c value for any polymer, are within a narrow range, from the onset of indentation. Combining residual profiles via scanning probe microscopy with mathematical modeling of the indenter tip, provides the strain distribution beneath the tip. CSS measures examined here, indicate polymer-specific regions to regions common to glassy polymers, which are reached very early in the nanoindentation.
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