Characterisation of Pressure-sensitive Yielding in Polymers

摘要

In this paper, the confined compression test set-up [Ma and Ravichandar (2000) Experimental Mechanics vol. 40, pp. 38-45] is employed to characterise the pressure-dependent yield behaviour of polymers. Attention is restricted to polymethyl methacrylate (PMMA) which is assumed to obey the Drucker-Prager yield function. The main objective is to develop a method for analysing the results of the above test procedure in order to obtain the pressure sensitivity index of the material. Furthermore, a technique for generating different stress histories in the specimen is explored by varying the initial clearance between the cylindrical specimen and the confining ring. In order to confirm the result obtained from the confined compression test, spherical indentation experiments in which high hydrostatic pressure is generated in the plastic zone underneath the indenter are carried out with the same PMMA material. The data obtained from these experiments are interpreted by performing finite element analyses assuming several values for the pressure sensitivity index of the material. It is shown that the hardness depends markedly on the above index. This dependence can be exploited to determine it from indentation experiments using an inverse approach.