3D Damage Micromechanisms in Polyamide 6 Ahead of a Severe Notch Studied byIn SituSynchrotron Laminography

International audience; Micro-damage mechanisms in a semicrystalline PolyAmide 6 polymer were characterized by in situ synchrotron radiation computed laminog-raphy (SRCL) using compact-tension like specimens with a notch root radius of 0.25 mm. SRCL allows the quantification of cavity nu-cleation, growth and coalescence in flat 2 mm-thick notched specimens with a micrometer resolution in 3D (under conditions of severe stress triaxiality) during the in situ loading. The maximum damage occurred at mid-thickness and was located at a small distance ∼ 200 µm from the notch root. It is shown that damage was distributed in distinct zones, that could be linked to different stress triaxiality states. Penny shaped cracks were found after some loadings. Their diameters were a function of the distance to the notch root: In a layer of about 33 µm no damage was found. In the adjacent 128 µm layer penny-shaped cracks were found with diameters of the order of average spherulite sizes (4-6 µm). In the next region 30-45 µm long cracks were found corresponding to several average spherulite diameters. During propagation, tunnel-like cracks formed ahead of the main crack. Finally, crack initiation location was found to be largely dependent on the roughness of the machined notch surface by comparing two samples with the same loading conditions.