Lin Hui, Jin Tao, Lv Lin, Ai Qinglin
Key Laboratory of E&M, Ministry of Education & Zhejiang Province, Zhejiang University of Technology, Hangzhou 310014, China.
Zhejiang Industry Polytechnic College, Shaoxing 312000, China.
Polymers (Basel). 2019 Mar 4;11(3):412. doi: 10.3390/polym11030412.
Indentation size effects in poly(methyl methacrylate) (PMMA) were studied through nanoindentation. Two factors of indentation size effects in PMMA, namely yield criterion and shear transformation-mediated plasticity, were analysed in detail. The yield criterion that considers strength differential (SD) effects and pressure sensitivity was constructed by performing the combined shear-compression experiments. The relationship between hardness and normal stress can then be obtained based on Tabot's relation. Shear transformation-mediated plasticity was also applied to model the measured hardness as a function of the indentation depth at different strain rates. Results show that the yield criterion contains the terms of SD effects and pressure sensitivity gives the best description of the yielding of PMMA. Additionally, the volume of single shear transformation zone calculated through the presented criterion agrees well with simulation and exhibits increases with increasing strain rate. Indentation size effects in PMMA under different strain rates were discussed and an appropriate indentation depth range was suggested for calculating the hardness and modulus.
通过纳米压痕研究了聚甲基丙烯酸甲酯（PMMA）中的压痕尺寸效应。详细分析了PMMA中压痕尺寸效应的两个因素，即屈服准则和剪切转变介导的塑性。通过进行剪切-压缩联合实验，构建了考虑强度差（SD）效应和压力敏感性的屈服准则。然后可以根据塔波特关系获得硬度与法向应力之间的关系。还应用剪切转变介导的塑性来模拟在不同应变速率下压痕深度函数的测量硬度。结果表明，屈服准则包含SD效应项，压力敏感性对PMMA的屈服给出了最佳描述。此外，通过所提出的准则计算出的单个剪切转变区的体积与模拟结果吻合良好，并且随着应变速率的增加而增大。讨论了不同应变速率下PMMA中的压痕尺寸效应，并提出了用于计算硬度和模量的合适压痕深度范围。
