Comportamento mecânico de compósitos poliméricos híbridos: estudos experimentais, analíticos e numéricos

Abstract

Hybrid synthetic fiber-based fabrics have been developed by the industrial sector as a new reinforcement alternative for polymer composites. In this respect, there is a need to know the mechanical characteristics of these hybrid polymer composite fabrics, which have been little studied to date. Under project conditions, three characteristics are significant: anisotropy, geometric discontinuities and type of hybridization. This thesis aims to investigate all of these influences by studying two composite laminates, using two fabrics: a hybrid carbon/glass fiber fabric and a hybrid carbon/aramid fiber fabric, both with epoxy vinyl ester resin as matrix. The manufacturing process used was hand lay-up to obtain the laminates. Uniaxial tensile tests were conducted on test specimens so that all the different types of fibers were oriented in the direction of the applied load, in addition to fiber orientation at ±45° in order to determine the shear behavior of the laminates. The tests were carried out in both the original condition (without hole) and with geometric discontinuity (characterized as a central hole, whose diameter was variable for orientation of high mechanic performance fiber). A number of studies on ultimate strength and fracture mechanics characteristics (macroscopic and microscopic) have been conducted. To determine the influence of the w/D ratio (width of test specimen/diameter of the hole), an analytical study was performed based on stress concentration using Point Stress Criterion (PSC) and Average Stress Criterion (ASC) failure theories, as well as a numerical study using the Finite Elements Method. In these studies, the primary objective is to determine the stress concentration factor (K) of the proposed materials, using both the influence of elastic modulus and geometric parameters. The studies showed that mechanical behavior and fracture characteristics were strongly influenced by anisotropy, hybridization and geometric discontinuity. The analytical and numerical models obtained results showing good agreement with those reported in the literature.