Laminado compósito a base de tecido híbrido: anisotropia, furo concêntrico, fratura mecânica e análise por MEF

Abstract

Composite materials consist of an agglutinative phase (matrix) and another (reinforcements) that provides them with sustainability and load bearing capacity. Their multiple applications, possible uses and always innovative conceptions mean they are being increasingly used in technological fields, in both research and industrial use. Matrices and reinforcements bind without fusion, conserving their particular characteristics, but providing novel properties to the new material formed for a given purpose. In this respect, the present study designed a based epoxy vinyl ester thermoset polymer resin laminate composite, reinforced with eight layers of a bidirectional hybrid fabric consisting of Kevlar fibers in the warp direction and carbon fibers in the weft direction; this composite material was denominated CL (carbon/Kevlar bidirectional hybrid fabric-based composite laminate). The mechanical behavior study of this CL laminate composite was conducted using an experimental, analytical and numerical approach with the general aim of determining its mechanical properties (primarily ultimate tensile strength and modulus of elasticity), considering the anisotropy of the hybrid fabric and the presence of geometric discontinuity (circular hole). In the event of geometric discontinuity, distances characteristics “ao” and “do”, corresponding to the Average Stress Criterion (ASC) and Point Stress Criterion (PSC), were determined, characterizing the extent of stress concentration around the hole. Numerical focus consists of analyzing the behavior of two proposed semiempirical models, simulated using the finite element method (FEM) and referenced respectively as HA-SFFP/H (Influence of the Concentric Hole/Anisotropy in the Stress Field and Failure Prevention), for the test specimens with concentric hole and HA-SFFP/O for the test specimens without concentric hole (original condition). The entire mechanical behavior study was based on the uniaxial tensile test. The physical characterization of the CL laminate was conducted using volumetric density and calcination tests, the latter to obtain levels (percentages) of microstructural parameters (matrix, fibers and voids). Mechanical fracture analysis was carried out using a scanning electron microscope (SEM), in order to identify microstructural damage. In general, anisotropy and the presence of a circular hole directly influenced the results. The semiempirical models proposed were satisfactory in their predictions, mainly the model based on the Point Stress Criterion.