Evaluation of polymer viscoelasticity by integrated micro-indentation test with optical flow algorithm

Abstract

This study aims to directly evaluate the viscoelastic (creep) parameters of polymer materials by integrating a micro-indentation test with an optical flow (OF) algorithm and an embedded center of dilatation (ECD) model. After indentation, the in-plane displacement field on the specimen surface is measured over time using the OF algorithm, thereby capturing the recovery behavior of the indentation imprint. Subsequently, the creep strain evolution curve over time is obtained through displacement and spatial differentiation. The ECD model is employed to estimate the initial residual stress induced by indentation process without resorting to complex inverse analysis. The reliability of estimated surface residual stress was validated through FEA. A time hardening model is then used to derive the creep strain-time relationship. Using the initial residual stress and the creep strain curve obtained from indentation, the time hardening creep parameters are determined. The experimental tests on polymethyl methacrylate (PMMA) and polycarbonate (PC) have demonstrated that the proposed method yields creep parameters within an approximate 5% error margin relative to conventional tensile creep tests.