Estudo da progressão de danos em materiais compósitos (fibra de carbono/epóxi) sob fadiga em compressão

Abstract

The use of composite materials in the most varied industrial sectors has increased considerably in recent years, especially those reinforced with bidirectional carbon fiber/epoxy resin fabrics. These, in the most varied applications in which they are used, experience several types of possible requests, one of them being compression requests. With this increasing use and reports of failures in structures, when submitted to compression requests, there is a need to better understand their behavior when exposed to this type of request. In this context, an experimental set of data to measure damage progression, considering cyclic loads in compression of a bidirectional composite laminate, is presented, involving static and fatigue mechanical characterization, identification of the fatigue deformation limit for lives up to 120,000 cycles and 240,000 cycles, damage mapping through damage parameters extracted from hysteresis cycles, deformation gradient data extracted by Digital Image Correlation (DIC), temperature data obtained by a thermographic camera, characterization of failure modes, and results of a study on the failure mechanisms, performed by scanning electron microscopy (SEM). Although many studies have been reported in the literature on damage progression in composite materials, very few have focused on the analysis of compression fatigue in bidirectional composites using analytical, numerical, and experimental analyses. Thermography proved to be useful in the rapid assessment of fatigue damage and in determining the fatigue strength limit. By obtaining the hysteresis cycles, a mapping of the damage progression for stresses close to the deformation limit was carried out, using the accumulated damage index, loss fator, and stiffness degradation. With the deformation maps obtained by DIC, it was observed that the deformations are not uniform along the surface of the sample, showing that the composite material exhibits an intrinsic mechanical heterogeneity. Finally, fractographic aspects of the fracture surfaces of samples from static, fatigue, and hysteresis tests were analyzed by scanning electron microscopy. The analyses showed that the fracture surfaces were rich in fractographic aspects, and how important is the use of this tool for understanding how the combination of different failure mechanisms interacts and leads to failure of the composite material.