Deep penetration micro-indentation testing of high density polyethylene

The deep penetration micro-indentation test of high density polyethylene has been analyzed in terms of the opening of a cavity in front of the indenter. The expansion of a cylindrical cavity opening under an internal pressure, as previously considered by Wright et al., has been compared to the opening of a spherical cavity. These model predictions have been tested experimentally using a small diameter (36 μm), flat cylindrical indenter. The micro-indenter was driven by a piezo-electric transducer under displacement control. The test data could be fitted more closely to a spherical cavity model, taking into account varying crystallinity in the sample and varying strain rate in the test. The plastic properties of the sample could thus be measured accurately from point to point, with a spatial resolution dependent on the indenter diameter. Microstructural examination of the spherulitic distortions under a large diameter (1 mm) tip showed a conical zone of little plastic deformation moving ahead of the tip.