Damage mechanisms of amorphous and low semi-crystalline polymers under tensile deformation studied by Ultra Small Angles X-ray Scattering

• Published in: Macromolecules 2020-06, Vol.53 (13), p.5538-5559
• Main Authors: Djukic, Stéphanie, Bocahut, Anthony, Bikard, Jérôme, Long, Didier R
• Format: Article
• Language: English
• Subjects: Engineering Sciences
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.0c00534

We investigate the damage mechanisms of amorphous and low semi-crystalline semi-aromatic polyamides, polyphthalamides (PPA) and two other amorphous polymers, polycarbonate (PC) and poly(metyl)methacrylate (PMMA) under tensile deformation. Ultra-Small Angles X-ray Scattering (USAXS) experiments permit to describe the beginning of the damage and the growth of crazes. Interpreting the results allows to measure the volume fractions of damages, as well as their distribution of sizes at different stages of tensile deformation. Different modes of damage are observed. They are initiated by the nucleation of nanometric crazes around pre-existing defects for PC, PMMA and the amorphous polyamide. Then the growth of these crazes is blocked by the strain hardening at the local level. By increasing the strain further, the growth of a second family of large crazes is observed for these three polymers before the yielding which leads to fracture for PC and PMMA far in the macroscopic strain hardening regime, but not for the amorphous polyamide for which damaged is stabilized after the stress softening and in the ensuing necking regime for which strain hardening is also observed. In the case of two low semi-crystalline polyamides, no damage is observed at all and deformation takes place by necking without damaging and breaking. We propose interpretations for these different behaviors.