The polymethyl methacrylate (PMMA) subjected to hygrothermal aging was applied to nanoindentation tests under different indentation strain rates. The influences of hygrothermal aging on the indentation behaviors of PMMA are discussed. Results show that the indentation elastic modulus and hardness decrease with increasing aging time. Furthermore, the indentation size effects (ISE) can be observed in aged PMMA specimens as they are sensitive to aging time as well as to the indentation strain rate. The quantitative analysis of ISE is proposed on the basis of shear transformation-mediated plasticity and was presented in our companion paper.

中文翻译：

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研究湿热老化对PMMA压痕尺寸效应和微压痕测量的影响。第一部分：实验结果

将经过湿热老化的聚甲基丙烯酸甲酯（PMMA）应用于不同压痕应变速率下的纳米压痕测试。讨论了湿热老化对PMMA压痕行为的影响。结果表明，压痕弹性模量和硬度随着时效时间的增加而降低。此外，在老化的PMMA标本中可以观察到压痕尺寸效应（ISE），因为它们对时效时间以及压痕应变速率敏感。ISE的定量分析是在剪切转换介导的可塑性的基础上提出的，并在我们的配套论文中介绍了。