Scratch and indentation tests on polyoxymethylene (POM)

Abstract

Scratch and indentation tests were performed on a polyoxymethylene homopolymer that was molded using three different mold temperatures. The different microstructures that developed during processing were studied by examining two samples for each mold temperature at different depths. During the scratch tests, the normal and the tangential force were recorded. The tests on the “as-molded” surface, in comparison to those that were polished until 1 mm of the material was removed, showed extrema of the normal force at a scratch depth that correspond to the interface of different regimes in the microstructure. The first extremum was considered to be caused by the breaking of the skin layer of the polymer (as a result of the rapid cooling process in the mold). Further extrema correspond to the permeation of the transition zone of the indenter into the spherulitic core of the sample. Indentation tests that were made on the same samples showed that the skin had a slightly lower hardness than the bulk of the polymer and that the difference in hardness decreases with increasing mold temperature. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1985–1996, 1997