Experimental investigation and constitutive modeling of rubbery polymers.

Abstract

The strain rate response of rubbery materials is receiving an increasing amount of attention in academic and industrial research. The high strain rate response is of particular interest in areas such as automotive and aerospace crash-worthiness and impacts. Moreover, the development of constitutive models valid over a range of strain rates from quasi-static to wave propagation rates is required for implementation into finite element and finite difference programs to simulate high rate deformations. An experimental investigation of strain rate effects in plasticized polyvinyl chloride (PPVC) subjected to large, uniaxial deformations was conducted over a large range of strain rates. Low strain rate, uniaxial compression tests were used to characterize the influences of temperature and plasticizer content in PVC. Additional characterization techniques including differential scanning calorimetry, thermal-mechanical analysis, and wide angle X-ray scattering, were employed to gain insight into the morphology and potential molecular origins for the responses that the PPVC exhibits under low strain rate test conditions. High strain rate tests were conducted using the split Hopkinson pressure bar (SHPB) technique. A SHPB was designed for the express purpose of testing soft materials and is shown to be capable of compressing soft materials at fairly uniform, large true strain rates to finite deformations. A high-speed digital camera was used to verify the strains computed with one dimensional wave propagation equations. The high-speed photographic history of the experiment was also used to calculate radial expansion. Modifications to the Arruda-Boyce glassy polymer model were made to account for the initial nonlinearity, the reduction in yield stress and plastic deformation and the large hysteresis loops caused by the addition of plasticizer to PVC. The modified model predicts the loading and unloading data of the PPVC from constant, low strain rate, uniaxial compression experiments.