DEEP PENETRATION MICRO-INDENTATION TESTING OF HIGH-DENSITY POLYETHYLENE

The deep penetration micro-indentation test of high density polyethyle ne has been analyzed in terms of the opening of a cavity in front of t he indenter. The expansion of a cylindrical cavity opening under an in ternal pressure, as previously considered by Wright et al., has been c ompared to the opening of a spherical cavity. These model predictions have been tested experimentally using a small diameter (36 mu m), flat cylindrical indenter. The micro-indenter was driven by a piezo-electr ic transducer under displacement control. The test data could be fitte d more closely to a spherical cavity model, taking into account varyin g crystallinity in the sample and varying strain rate in the test. The plastic properties of the sample could thus be measured accurately fr om 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 plas tic deformation moving ahead of the tip. (C) 1998 Elsevier Science S.A . All rights reserved.