Experimental investigations and modeling of volume change induced by void growth in polyamide 11

Polymers are known to be sensitive to hydrostatic pressure. The influence of stress triaxiality ratio on cavitation and damage has been highlighted in numerous studies. This paper proposes experimental investigations allowing the control of both the stress triaxiality ratio and the void distribution via microscopic observations of microtome-cut surfaces from interrupted tests. With the help of a finite element code, the Gurson–Tvergaard–Needleman model was calibrated by using these multi-scale experimental data. Then comparison between both numerical and analytical models and experimental data was performed. Bridgman formulae were reported to be valid up to the peak load. Moreover, a better understanding of the time evolution of significant parameters such as the porosity (volume change) and the stress triaxiality ratio (hydrostatic pressure), was highlighted.

► Quantification of the void volume fraction (damage) by carrying out interrupted tests on axi-symmetrically notched specimens with various notch root radii.
► Details of the multiaxial stress/strain fields according to the notch root radius.
► Description of the distributions of porosity in the minimum cross sections depending on the notch root radius.
► Use of these experimental data for calibrating the material coefficients for constitutive model used in finite element analyses.
► Comparison between analytical and numerical simulations of hydrostatic pressure versus volume change for semi-crystalline polymers: limits of analytical model.