| Summary: | 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 Rhe 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. Rhev+Rhvfirst 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.
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