| Summary: | The nanoindentation results of Polymethyl Methacrylate (PMMA) after hygrothermal aging under different indentation strain rates are analyzed. The influences of hygrothermal aging on its indentation size effects (ISE) and microindentation measurements are discussed. The theory of shear transformation plasticity is utilized to analyze the ISE of PMMA after hygrothermal aging. The shear transformation zone (STz) sizes of PMMA under different conditions have been calculated and can be continuously described by aging time and strain rate. The characteristic deep, which represents the vanishment of ISE, is obtained and exhibits increases with strain rate and aging time. The objective measurements (i.e., elastic modulus and hardness) that represent the practical properties of the aged PMMA can be calculated: elastic modulus and hardness decrease with aging time. The effects of aging on the mechanical properties weaken with the increase with aging time, which results from the variation in the micro-mechanism. The prediction model can be constructed to explain the ISE of PMMA after hygrothermal aging through relating χ with aging time and strain rate. The proposed model agrees well with the experimental results.
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