Photoelastic evaluation of fiber surface-treatments on the interfacial performance of a polyester fiber/epoxy model composite

Abstract

Abstract:The interfacial adhesion between a polyester fiber and an epoxy matrix was improved by chemical and topological modifications of the fiber surface. The maximum interfacial shear strength was measured using photoelasticity to assess the interfacial performance in pull-out single-fiber composite specimens. An increase of the interfacial shear strength was observed when plasma-treated or surface-modified fibers were used; also, as the applied load to the free fiber was increased, the fiber treatment caused a reduction of the debonded area at the fiber-matrix interface.

Photoelastic and numerical analyses of the stress distribution around a fiber in a pull‐out test for a thermoplastic fiber/epoxy resin composite

“…An alternative solution for engineering applications, where high toughness is required rather than high strength is the employment of thermoplastic fibers as reinforcement. These fibers have been used to reinforce thermoplastic matrices , thermoset matrices and foam concrete composites resulting in a good mechanical performance.…”

“…Mechanical properties in polymer matrix composites are influenced by the interaction between the matrix and the reinforcement , thus, a good understanding of the interface performance and matrix‐fiber stress transfer in thermoset‐based composites with thermoplastic fiber reinforcement is crucial. The well‐known low compatibility between thermoplastic fibers and thermosetting matrices may lead to a weak fiber‐matrix interface . One of the methods most commonly used to study the interfacial adhesion in composite materials is the pull‐out test, which provides a direct way to measure the interfacial parameters such as adhesion and coefficient of friction and to monitor failure and debonding at the interface .…”

“…In this test, a single embedded fiber may be pulled out of the matrix, which can be a block of resin, a disc, or a droplet . The pull‐out test has been successfully utilized to study the performance of thermoplastic fiber/thermoset matrix systems, for example, poly‐p‐phenylenebenzobizoxazole (PBO)/epoxy , PE/epoxy and polyester (PET)/epoxy . Several studies have described the pull‐out test analytically ; however, the interpretation of the single‐fiber pull‐out test, based solely on a theoretical approach, may be inaccurate when a complex state of stress is present due non‐ideal conditions such as, imperfections, non‐homogenous bonding, debonded areas and plasticity .…”

“…The pull‐out test has been successfully utilized to study the performance of thermoplastic fiber/thermoset matrix systems, for example, poly‐p‐phenylenebenzobizoxazole (PBO)/epoxy , PE/epoxy and polyester (PET)/epoxy . Several studies have described the pull‐out test analytically ; however, the interpretation of the single‐fiber pull‐out test, based solely on a theoretical approach, may be inaccurate when a complex state of stress is present due non‐ideal conditions such as, imperfections, non‐homogenous bonding, debonded areas and plasticity . This complex state of stress can be analyzed experimentally with the well‐known photoelasticity technique, which has been successfully employed to measure the stress fields and the debonding process at a fibre/matrix interface .…”

“…New techniques to measure in situ stress fields in composites such as digital image correlation are being increasingly used; however, photoelasticity still remains as a well‐established technique that provides reliable results with minimum investment in equipment. Photoelasticity also allows in situ analysis of the loading/deformation process of a specimen and the observation of stress distribution . Photoelastic studies of the pull‐out test in thermoplastic fiber/thermoset matrix systems have been performed to study their interface, for example, PET/epoxy composites , which provided the interfacial shear stress distribution directly from the image of isochromatic fringes; however, a complete study of the stress fields in this system, which includes the directions and distribution of the principal stresses in the matrix due to stress transfer, has not been reported.…”