Discrete deconvolution to extract viscoelastic material properties from spherical nanoindentation

Abstract

This study looks at how discrete deconvolution can be used to extract the relaxation modulus and creep compliance of polymers from spherical nanoindentation load-displacement curves. It was used to extract viscoelastic material properties from three commercially available polymers; polycarbonate (PC), polymethyl methacrylate (PMMA), and low-density polyethylene (LDPE) using three different indenter sizes. The average instantaneous modulus obtained by nanoindentation was 2.96 GPa, 2.14 GPa, and 0.265 GPa for PMMA, PC, and LDPE respectively. The average creep compliance obtained was 0.43-0.034e^(-t/20)-0.057e^(-t/220), 0.49-0.015e^(-t/12)-0.013e^(-t/150), and 6.59-1.17e^(-t/15)-1.64e^(-t/146) for PMMA, PC, and LDPE respectively. The average relaxation modulus obtained was 2.34+0.28e^(-t/17)+0.34e^(-t/192), 2.02+0.067e^(-t/12)+0.055e^(-t/145), and 0.152+0.067e^(-t/12)+0.047e^(-t/111) for PMMA, PC, and LDPE respectively. It is shown that the properties extracted were consistent across the three indenter tip sizes and similar to other results found in literature. The results suggest that viscoelastic properties can be reliably extracted at the microscale for different types of polymers using spherical nanoindentation.