Abstract
Indentation size effects in poly(methyl methacrylate) (PMMA) were studied through nanoindentation. Two factors of indentation size effects in PMMA, namely yield criterion and shear transformation-mediated plasticity, were analysed in detail. The yield criterion that considers strength differential (SD) effects and pressure sensitivity was constructed by performing the combined shear-compression experiments. The relationship between hardness and normal stress can then be obtained based on Tabot’s relation. Shear transformation-mediated plasticity was also applied to model the measured hardness as a function of the indentation depth at different strain rates. Results show that the yield criterion contains the terms of SD effects and pressure sensitivity gives the best description of the yielding of PMMA. Additionally, the volume of single shear transformation zone calculated through the presented criterion agrees well with simulation and exhibits increases with increasing strain rate. Indentation size effects in PMMA under different strain rates were discussed and an appropriate indentation depth range was suggested for calculating the hardness and modulus.
Highlights
Poly(methyl methacrylate) (PMMA) is a widely used material in the field of aircraft and automotive industries due to its excellent properties such as transparency, low density, and high impact resistance [1,2,3,4]
From the compressive and tensile tests of poly(methyl methacrylate) (PMMA), the strength of compression was found different from that of tension [9]. This phenomenon is the so-called strength differential (SD) effects, which results from the different deformation mechanisms, indicating that the yielding of PMMA
The PMMA sheet is produced through a traditional cell cast method, no molecular chain orientation exists in the as-cast sheet
Summary
Poly(methyl methacrylate) (PMMA) is a widely used material in the field of aircraft and automotive industries due to its excellent properties such as transparency, low density, and high impact resistance [1,2,3,4]. Many studies have been conducted to investigate the macroscopic [5,6] and mesoscopic [7,8] mechanical properties of PMMA such as compression, tension, and nanoindentation. The yield strength and modulus of PMMA were found to be sensitive to strain rate and both properties exhibit increases with strain rate. From the compressive and tensile tests of PMMA, the strength of compression was found different from that of tension [9]. This phenomenon is the so-called strength differential (SD) effects, which results from the different deformation mechanisms (flow or fracture of molecular chain, crazing or formation of micro cavities), indicating that the yielding of PMMA is sensitive to the sign of normal stress.
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