Linear analysis of the viscoelastic response of polymer micro-pillars using the open-loop flat punch indentation test

Abstract

A method for testing the viscoelastic property of polymer micro-pillars, based on open-loop flat punch indentation, is presented. The difficulties in performing a conventional creep or stress relaxation test using a nanoindentation apparatus with a leaf-spring structure are described and the advantages of our method explained. An analytic model for the test was devised and a simple formula for measuring creep compliance provided. As an example, polymer micro-pillars were fabricated on a glass substrate using nano-stereolithography (NSL) and their creep compliance measured. Experimental details are presented, including testing procedure, processing of raw data and analysis of test results, plus some issues, related to measurement uncertainty, are discussed, such as sensor resolution, parallelism, thermal drift and damping force.