Abstract The effects of aging time on indentation creep behaviors of Polymethyl methacrylate (PMMA) have been investigated and the creep displacement was found to increase with aging time. However, the rate of change weakens as aging time increases. The generalized Calvin model consists of three Voigt elements that provide a good description of the indentation creep behavior of PMMA during the holding stage. Each Voigt element represents the motions with different levels i.e. molecular chain, molecular chain segments, molecular chain linkage, and branched-chain. The motions of molecular chain with different levels always have different delay times. The mechanism on the effects of aging time on the indentation creep responses is analyzed by comparing the contributions of different deformation types to total deformation. The contribution of elastic deformation to the total deformation R h e decreases initially and then increases as aging time increases, which indicates the weakening of elastic modulus results from hygrothermal aging. With the aging time increasing, the contribution of time-dependent deformation to the total deformation i.e. R h e v + R h v first increases and then decreases, which can be attributed to the different aging mechanisms at different stages. Further studies on the effects of aging time on creep compliance and time delay spectrum of PMMA during the holding stage indicates different deformation levels of PMMA characterized by different Voigt elements.

中文翻译：

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湿热老化对PMMA压痕蠕变行为影响的实验研究

摘要 研究了老化时间对聚甲基丙烯酸甲酯 (PMMA) 压痕蠕变行为的影响，发现蠕变位移随老化时间而增加。但是，随着老化时间的增加，变化率会减弱。广义 Calvin 模型由三个 Voigt 元素组成，它们很好地描述了 PMMA 在保持阶段的压痕蠕变行为。每个 Voigt 元素代表不同层次的运动，即分子链、分子链段、分子链连接和支链。不同能级的分子链运动总是有不同的延迟时间。通过比较不同变形类型对总变形的贡献，分析时效时间对压痕蠕变响应的影响机制。弹性变形对总变形R he 的贡献随着老化时间的增加先减小后增加，表明湿热老化导致弹性模量减弱。随着时效时间的增加，时效变形对总变形的贡献即R hev + R hv 先增加后减小，这可以归因于不同阶段的不同时效机制。进一步研究时效时间对保压阶段 PMMA 蠕变柔量和时间延迟谱的影响表明，不同 Voigt 元素的 PMMA 具有不同的变形水平。随着时效时间的增加，时效变形对总变形的贡献即R hev + R hv 先增加后减小，这可以归因于不同阶段的不同时效机制。进一步研究时效时间对保压阶段 PMMA 蠕变柔量和时间延迟谱的影响表明，不同 Voigt 元素的 PMMA 具有不同的变形水平。随着时效时间的增加，时效变形对总变形的贡献即R hev + R hv 先增加后减小，这可以归因于不同阶段的不同时效机制。进一步研究时效时间对保压阶段 PMMA 蠕变柔量和时间延迟谱的影响表明，不同 Voigt 元素的 PMMA 具有不同的变形水平。