Indentation as a probe for the post - yield behavior of glassy polymers

This report describes a first study into the possibility of developing a hybrid experimental/numerical technique that enables the full characterization of the finite strain behavior of glassy polymers such as polycarbonate and polystyrene. The numerical and experimental techniques involved are Finite Element Models based on a finite strain elasto-viscoplastic constitutive model and indentation measurements in which a flat-tip indenter is used. Conclusions: The results of this study show that the combination of the experimental and numerical techniques used are promising. The numerical model is capable of giving good qualitative descriptions of the behavior observed experimentally. However, quantitative comparison is still a problem. A rather large difference between the numerical and experimental indentation load-displacement curves has been found. Several possible causes for this difference have been investigated, such as friction, indenter geometry and residual stresses. None of these led to the solution of the problem. The current opinion is that the deviations are caused by imperfections of the constitutive equation. In particular, it is suggested that the way in which pressure dependence is incorporated in the constitutive equation is not fully adequate.