In Situ tensile tests to analyze the mechanical response, crack initiation, and crack propagation in single polyamide 66 fibers

Abstract

Single fiber mechanical testing is challenging to perform, especially when the diameter is as small as tens of micrometers. For this reason, real‐time observations of crack propagation mechanisms have been rarely been investigated experimentally. This article presents experimental and numerical investigations of fracture of monofilamentary high performance polyamide 66 fibers. Their engineering stress–strain curves are compared. The mechanisms of failure starting from crack initiation until the final brittle fracture are studied by in situ tests in Scanning Electron and optical microscopes. Finite element modeling at the individual fiber scale has been performed in three‐dimensional (3D), as a reverse engineering method. The compliance method was used to determine the crack depth that triggers the final failure. The fracture toughness was numerically determined using the J‐integral concept, accounting for the geometry of the crack front (3D) together with plastic deformation. 3D meshes were designed especially from postmortem observations. The average value deduced was about 47 ± 7 kJ m−2, which will be discussed with other estimates using linear elastic fracture mechanics. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 680–690

Mechanisms of damage and fracture of aramid fibers: Focus on the role of microfibril cooperativity in fracture toughness

“…Because of the small diameter of the fiber and the quasi‐instantaneous failure, no damage mechanisms or crack propagation have been reported in the literature so far. More generally, damage mechanisms of polymer fibers have been scarcely studied 5 . Performing a tensile test, step by step, in a SEM chamber, damage mechanisms have been observed from damage initiation to the total failure of the fiber (Figure 3 and Video S1).…”

“…More generally, damage mechanisms of polymer fibers have been scarcely studied. 5 Performing a tensile test, step by step, in a SEM chamber, damage mechanisms have been observed from damage initiation to the total failure of the fiber (Figure 3 and Video S1).…”

“…Clearly, this sudden breakage is complicated to observe in real time. During the last few years, first in situ observations of damage and fracture mechanisms of fiber have been carried out on raffia fibers 18 or Nylon 66, 5 and more recently on aramid fibers 16,19–21 . Under optical microscope, fibrillation and fiber splitting during failure was observed shortly before the final fracture of the fiber 19,20 .…”

“…From a fundamental point of view, the exact contribution of the single fiber behavior to the assembly performance is still misunderstood. 4 Mechanical characterization at the single fiber scale (diameter ffi 10 μm) [5][6][7] seems essential-even if it is difficultto understand and rationalize the performances at the rope or product scale.…”

Ductile crack initiation and growth on a plasticized Polyvinylchloride during air bag deployment

“…The numerical approach used here did not intend to predict the failure of the specimen but dealt with a FE simulation of the crack propagation by imposing the history of the crack extension included in the experimental data from video camera acquisition. An attempt was then made to simulate the crack initiation and growth using the łrelease nodal degree of freedomž (rndof) technique (Laiarinandrasana et al 2006;Marcellan et al 2019). This was achieved numerically by releasing gradually the nodes (in six steps for three quadratic elements) from the initial to the final remaining ligament, following the crack growth rate obtained experimentally.…”