HIGH-STRAIN-RATE PROPERTIES OF POLYMETHYL METHACRYLATE

摘要

Stress-strain curves of polymethyl methacrylate (PMMA) are determined in a wide range of strain rates under conditions of uniaxial strain. A plate impact testing apparatus, a drop hammer testing machine and a universal testing machine are used for the high strain-rate (10~7 s~(-1)), medium strain rate (10~2s~(-1)) and low strain rate (10~(-4) s~(-1)) tests, respectively. The plate impact test is used to obtain stress-strain curves for PMMA undergoing uniaxial strain. Stress-time histories are obtained in PMMA at impact velocities 490 to 740 m/s using polyvinylidene fluoride (PVDF) gauges. Lagrangian analysis is used to extract strain-time histories from the experimental stress data. The drop hammer compression test is used to determine stress-strain curves at medium strain rate under conditions of uniaxial stress by using an extrapolation procedure. For the low strain rates the stress-strain curves are determined under conditions of uniaxial stress by the universal testing machine combined with the extrapolation method. The stress-strain curves at medium and low strain rates in uniaxial strain are constructed on the basis of the Wood's equation from the uniaxial stress data. It is assumed for strains up to roughly 0.1 that PMMA is elastic, perfectly plastic material and Young's modulus is rate dependent. The effect of strain rate on the stress of PMMA is investigated under conditions of uniaxial strain.