Place: EUROMAT 2011 - European Congress on Advanced Materials and Processes, Montpellier, France
Plastic yielding of glassy polymers leads to extreme localized deformation in the form of constant volume shear bands or zones of nano-scale fibrillation (crazing) triggered by cavitation. At macroscopic scale, both these form of localizations are controlled by the prevailing hydrostatic stresses and shear stresses. However, mechanistic understanding of the conditions that leads to localization at failure sites is still at large.
To this end, molecular dynamics deformation simulations are performed on glassy amorphous polymer represented by united atom model of amorphous polyethylene. Multi-axial loading condition are used to impose conditions for crazing and shear yielding type failure. At first, the length scale up to which a macroscopic failure criterion relates with local stress conditions is determined. It is found that average local stresses in a small volume element containing approximately 100 atoms or more obey the macroscopic failure criterion. Next, local plastic events are identified based on criterion of mean square non-affine displacements reaching the macroscopic yield values. Finally, deformation case leading to cavitational mode of localization is studied. It is found that the sites failing by localization are the ones having high accumulated plasticity.