Experimental characterisation of the dilation angle of polymers

Despite the wide use of Drucker-Prager plasticity-based models on polymers, the experimental measurement of the dilation angle, a critical parameter to fully describe the plastic potential, has been rarely reported in existing literature. This paper shows, for the first time, the experimental characterisation of the dilation angle of polymers over a wide range of plastic strain. These measurements were obtained from uniaxial compression experiments conducted on poly(methyl methacrylate) (PMMA) and an untoughened epoxy resin. The calculation of the dilation angle relied on the measurements of the compressive force and the strain components obtained via Digital Image Correlation (DIC). Lower values of dilation angle were obtained for the epoxy resin, suggesting that resistance to volumetric change during plastic deformation could be associated to molecular structure and internal forces. The methodology and results presented in this study can be applied to different types of materials and employed for developing and validating constitutive models that incorporate plastic dilation.