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This study aims to investigate the effects of strain rate on polymethyl methacrylate (PMMA) nanoindentation measurements. Nanoindentation experiments were used to characterize the mechanical properties of PMMA. A wide range of strain rates were employed to examine strain rate sensitivity of PMMA. The test results indicate that the elastic modulus and hardness of PMMA are strain-rate-dependent. In addition, both the elastic modulus and hardness of PMMA exhibit increases with increasing strain rate. However, the elastic modulus became a stable value until strain-rate of 0.2 s 21 . Creep behavior of PMMA under the condition of high strain rate is more obvious than that experience a low strain rate. Moreover, the effects of strain rate on the PMMA nanomechanical properties are detailed analyzed by discussing each stage of the indentation process.

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In this paper, the mechanical properties of CoCrFeNiAl0.3 high‐entropy alloy (HEA) under different strain rates are investigated using nanoindentation at room temperature. Experimental results show that the contact stiffness increases almost linearly with indentation depth and the elastic modulus is invariable under different indentation strain rates, while the indentation hardness under higher strain rate is relatively larger, and the hardness under large indentation depth is relatively smaller for each indentation strain rate. The indentation size effect of hardness and strain rate sensitivity exponent m under different indentation strain rates are analyzed, then the hardness and m free from the effect of indentation depth are obtained. Finally, this investigation reveals the size effects of the hardness of HEA in light of the strain rate sensitivity and activation volume of the dislocation nucleation.

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