3D Damage Micromechanisms in Polyamide 6 Ahead of a Severe Notch Studied by In Situ Synchrotron Laminography. Issue 5 (20th January 2016)

• Record Type: Journal Article
• Authors: Cheng, Yin; Laiarinandrasana, Lucien; Helfen, Lukas; Proudhon, Henry; Klinkova, Olga; Baumbach, Tilo; Morgeneyer, Thilo F.
• Is Part Of: Macromolecular chemistry and physics. Volume 217:Issue 5(2016:Mar.)
• Page Start: 701
• Page End: 715
• Publication Date: 2016-01-20
• Subjects: cavitation -- crack propagation -- damage micromechanisms -- in situ 3D microstructural characterization -- polyamide 6 (PA6) -- semicrystalline polymer -- triaxial stress -- X‐ray laminography; Polymers -- Periodicals; Polymerization -- Periodicals; Synthetic products -- Periodicals; Macromolecules -- Periodicals; 547.7
• DOI: 10.1002/macp.201500316
• Languages: English
• ISSNs: 1022-1352

Abstract

Abstract : Micro‐damage mechanisms in a semicrystalline polyamide 6 polymer are characterized by in situ synchrotron radiation computed laminography (SRCL) using compact‐tension like specimens with a notch root radius of 0.25 mm. SRCL allows the quantification of cavity nucleation, 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 is distributed in distinct zones, which can be linked to different stress triaxiality states. Penny‐shaped cracks are found after some loadings and their diameters are 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 are found with diameters of the order of average spherulite sizes (4–6 µm). In the next region, 30–45 µm long cracks are found corresponding to several average spherulite diameters. During propagation, tunnel‐like cracks are formed ahead of the main crack. Finally, crack initiation location is found to be largely dependent on the roughness of the machined notch surface by comparing two samples with the same loading conditions. Abstract : The in situ microdamage mechanisms in semicrystalline polyamide 6 are examined in 3D by X‐ray imaging for crack initiation and propagation in a large flat specimen. The characteristic sizes of the damage features are quantified. Distinct damage zones are found well distributed ahead of the initial notch, and characterized as a function of stress states. The formation of tunnel cracks during crack propagation and the effect of notch defect are discussed.