THE HIGH-STRAIN RATE BEHAVIOR OF POLYMERS

Experimental results are presented for the strain rate sensitivity of polycarbonate in the strain rate range 10(-4) to 10(4)s(-1), at 23 degrees C. The high strain rate tests are performed in a split Hopkinson pressure bar. Using thick specimens, there is an apparent increase in strain rate sensitivity in the high strain rate regime. This observed increase is significantly reduced when thinner specimens are employed suggesting that it does not represent inherent material behaviour. Numerical and analytical evidence is presented which shows that the apparent increase at high strain rates can be accounted for by stress wave propagation effects present in the test when high impact velocities are employed. The assumption of uniform stress and strain distribution within a split Hopkinson pressure bar specimen is therefore inappropriate at high impact velocities.