Dynamic Spall Failure of Polymers

The dynamic tensile spall failure strength of polymers subjected to high-pressure shock compression and high-strain-rate deformation is of increasing interest across a wide range of applications in extreme environments. Currently, there is no expansive database of polymeric materials for which spall strength properties are available. Plate-on-plate impact gas gun experiments were performed on 11 commercially available polymers using a multi-sample target configuration. The spall strengths obtained from velocity profiles captured using Photon Doppler Velocimetry interferometry for these polymers range from 25 to 160 MPa, with no direct correlation to their inherent characteristics, including the amorphous/semi-crystalline structure. A database of the spall strengths of 23 unique polymers, experimentally determined in this work and combined with those available in the literature, was created to include readily available mechanical and physical properties of the various polymers. The spall strength of most polymers is found to be typically higher than the corresponding quasi-static compressive and tensile strength values and about 30-50% of their bulk and elastic moduli, with some exceptions. Normalizing the spall strengths of the various polymers with respect to their calculated theoretical strength, and then correlating with their decompression (tensile) strain rate, reveals consistent trends similar to those for metals and alloys. Namely, the normalized spall strengths are nominally within 20% of the theoretical strength, although no obvious distinction between the spall failure response of the various polymer types based on amorphous or semi-crystalline structure is observed.