Damage based constitutive relationships in semi-crystalline polymer by using multi-mechanisms model

• A constitutive model accounting for the degree of crystallinity is proposed.
• The model is based on mechanics of porous media and handle volume change (damage).
• Tensile and X-ray tomography tests enabled local and global experimental database.
• The model captured radial and axial distributions together with voids orientation.

The deformation and damage micro-mechanisms of Polyamide 6 were investigated by using Synchrotron Radiation Tomography technique. To this end, notched round bars with two notch radii, enabling void growth mechanisms enhancement were used. Comprehensive scans allowed 3D representations of the permanent deformed and damaged microstructures. Morphology of porosity as well as void volume fraction distributions and orientations have been discussed regarding the level of hydrostatic stress submitted to polymer samples. Based on these experimental data, a multi-mechanism model coupled with damage formulation was proposed. The number of material parameters of the model was reduced to consider only those necessary to simulate notched specimens submitted to tensile load. The optimization strategy consisting of gathering global and local variables has been explained. The optimized set of material coefficients was able to reproduce the distributions of the void volume fraction as well as the orientation of aligned voids. The results highlighted the major role played by the stress tensor in void growth mechanisms.