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

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.

Microstructural observations supporting thermography measurements for short glass fibre thermoplastic composites under fatigue loading

“…9b. Moreover, even when there is no surrounding fibres, voiding of the matrix shows the same observation of alignment of pores with a main orientation perpendicular to the load direction [11]. As already mentioned, local orientations of the crack following the direction of fibres contributed to the global orientation perpendicular to the load direction.…”

“…The fatigue properties can be easily and quickly identified from 2D measurements. In parallel, computed tomography and computed laminography have developed rapidly to provide valuable information regarding microstructures and microscopic damage [2,[9][10][11]. Three-dimensional damage has now become accessible, and the determination of damage kinetics possible from the appearance of the very first micro-cracks to the complete fracture of the specimen is now possible.…”

Voiding Mechanisms in Deformed Polyamide 6 Observed at the Nanometric Scale

“…SRCT has been used to study notched round bars in PA6 deformed ex situ under steady strain rate or under steady load. , Microstructure of less dense matter, assumed to be voids, has been visualized in 3D with resolutions up to 0.7 μm, and spatial gradients of void volume fraction and void morphology have been studied. Indeed, the tomography and laminography techniques allow through thickness inspections of the samples . Notched round bars in PA11 deformed in situ have also been observed by SRCT in order to compare ex situ and in situ tests in terms of voiding phenomena.…”

Numerical validation framework for micromechanical simulations based on synchrotron 3D imaging

“…They enable the material microstructures and their degradation mechanisms to be assessed qualitatively and quantitatively [41]. In-situ experiments can also be performed to analyze the mechanical behavior of different materials [21,11,32,15]. Initially developed at synchrotron facilities [3], these tests are also performed at lab tomography set-ups [10].…”