Abstract:We present a method for evaluating the 3D refractive indices and 3D true stress and/or 3D true strain profiles of "isotactic polypropylene iPP" fibers during necking deformation. Observing the changes in geometrical shape during the deformation process is necessary to understand the mechanical performance of iPP fibers. 3D geometric shape profile and actual stress and strain profiles were measured for iPP fibers during the propagation of neck deformation. These measurements were performed with the aid of an in… Show more
“…From a formability standpoint, necking is the result of a competition between the decrease in cross-section and the hardening when the material is stretching. 48,49 As can be seen from Figure 14, 50,51 most probably, composites first elongated, then necking occurred, and finally, fracture has occurred. Figure 14.Schematic diagrams of the specimen fractures, (a) fracture of pure epoxy resin with a little amount of plastic deformation, (b) necking formation in nanocomposites, (c) fracture of nanocomposites after necking.…”
Recent developments in nanocomposites that are reinforced with polymeric fibers have heightened the need for a material in fast-moving parts of machines. The research to date has focused on tensile properties of nanocomposites reinforced with polymeric nanofibers, which were produced by the conventional methods. In this work, nanocomposites were fabricated by a novel approach that comprises epoxy resin, epoxy hardener, and PAN nanofibers in which the nanofibrous layer was placed in resin as spun during the electrospinning. Then, a nanocomposite with the same materials was made using the conventional method of layering. There were enhancements in elongation at break, fracture toughness, and stress at break of nanocomposites fabricated by in situ method in comparison with the nanocomposites fabricated using the conventional method of layering.
“…From a formability standpoint, necking is the result of a competition between the decrease in cross-section and the hardening when the material is stretching. 48,49 As can be seen from Figure 14, 50,51 most probably, composites first elongated, then necking occurred, and finally, fracture has occurred. Figure 14.Schematic diagrams of the specimen fractures, (a) fracture of pure epoxy resin with a little amount of plastic deformation, (b) necking formation in nanocomposites, (c) fracture of nanocomposites after necking.…”
Recent developments in nanocomposites that are reinforced with polymeric fibers have heightened the need for a material in fast-moving parts of machines. The research to date has focused on tensile properties of nanocomposites reinforced with polymeric nanofibers, which were produced by the conventional methods. In this work, nanocomposites were fabricated by a novel approach that comprises epoxy resin, epoxy hardener, and PAN nanofibers in which the nanofibrous layer was placed in resin as spun during the electrospinning. Then, a nanocomposite with the same materials was made using the conventional method of layering. There were enhancements in elongation at break, fracture toughness, and stress at break of nanocomposites fabricated by in situ method in comparison with the nanocomposites fabricated using the conventional method of layering.
Necking propagation (NP) is an important phenomenon that is facilitated by the superductility of many materials, although necking is often considered to be a type of unstable and heterogeneous deformation under tensile loading. In this study, the NP of samples produced with injection molding of polypropylene (PP) and high‐density polyethylene (HDPE) blends with or without a blowing agent was investigated by standard tensile testing, and the foam morphology and cellular structure were characterized with scanning electron microscopy. It was found that the foam parts fabricated with the PP/HDPE blends had the ability to be superductile under a low tensile test speed, which was attributed to the necking spreading throughout the tested gauge section stably and reliably. However, the NP of the foam PP/HDPE blend samples strongly depended on the distribution of the cellular foam. To investigate the relationship between the cellular structure and NP, a design of experiment approach based on the Taguchi method was used to fabricate many samples with different foam structures. The tensile test results of these samples suggested that the cellular uniformity, which was determined based on the statistical results of the fracture surface morphology, played an important role in the NP. The results suggested that there is a close relationship between the NP and the cellular uniformity. Using nonlinear fitting, it was straightforward to obtain a model between the NP length and cellular uniformity index for PP/HDPE molded foam parts.
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