Tensile yield in polyethylene

Uniaxial tension tests to the yield point were performed on polyethylene as a function of temperature from 21 to 117°C at a strain rate of 2 min−1. At 21, 45, and 69°C, measurements were also made at strain rates from 0.02 to 8 min−1. Yield energy was found to be a linear function of temperature extrapolating to zero at the melting point (140°C). The ratio of thermal to mechanical energy to produce yielding is about three times smaller than for glassy amorphous polymers. The ratio of yield stress to (initial) Young's modulus is 0.021 at room temperature and increases to 0.059 at 117°C. Also this ratio was found to decrease with log strain rate. For instance, at 21°C for a strain rate of 0.02 min−1 the value was 0.023, while at 8 min−1 this value decreased to 0.020.