Fractografia de Compósito Estrutural Aeronáutico Submetido ao Ensaio de Tenacidade à Fratura Interlaminar em Modo II

Abstract

Resumo: A fractografia consiste no estudo detalhado da morfologia da superfície de fratura de materiais. Para isto, a técnica de microscopia eletrônica de varredura (MEV) é usualmente utilizada para determinar a causa de falha e a relação do modo de falha com a microestrutura do material em análise. Essas informações permitem estabelecer analogia entre estrutura, propriedade e processamento do material com a iniciação e a propagação da falha. Neste estudo, a análise fractográfica é utilizada para investigar os aspectos que caracterizaram a falha por delaminação em Modo II de laminados poliméricos de uso estrutural. Para isto, espécimes com um inserto de Teflon  introduzido no plano médio de uma das extremidades do laminado (End-Notched) foram submetidos ao ensaio de carregamento em flexão em quatro pontos. Os espécimes foram preparados a partir de um laminado fabricado em autoclave, com camadas (0°, 90°) de material pré-impregnado de tecido bidirecional em estilo plain weave de fibras de carbono IM7/ resina epóxi M21. Os resultados da análise mostram que a superfície de fratura é muito irregular, com a visualização de fibras e impressões de fibras na matriz. Aspectos fractográficos de cúspides e formatos de concha, originados durante o cisalhamento da matriz polimérica, são também observados. Palavras-chave: Fractografia, laminado compósito, delaminação em Modo II. Fractography of Aeronautical Structural Composite Submitted to Mode II Interlaminar Fracture Toughness TestAbstract: Fractography involves a detailed study of the fractured surface morphology of materials. Usually the Scanning Electron Microscopy (SEM) technique is applied to investigate the cause of failure and the relationship between failure modes and the microstructure of the material under investigation. This information allows one to relate structure, processing methods and materials properties with the onset in their failure and propagation. In this study, fractographical analysis is employed to investigate the failure aspects induced by Mode II delamination of structural fiber-reinforced polymer composite laminates. Samples with Teflon  inserted at the mid-plane of one end of the laminate (end-notched specimens) were subjected to four-point bending (4-ENF) test. The samples were prepared from laminates manufactured in autoclave with prepreg layers (0°, 90°) of IM7 plain weave woven fabric fiber architecture and M21-epoxy resin. The results indicate that the fracture surface is very irregular where fibers and fiber prints at the matrix are visualized, along with fractographic aspects named cusps and scallops, formed during the polymeric matrix shearing.

Effects of moisture absorption on mechanical and viscoelastic properties in liquid thermoplastic resin/carbon fiber composites

“…In a general way, in the conditioned composites, the failure propagation was observed in the interfacial region, and in all SEM images, it was possible to notice the fibers striation showing a typical interfacial failure as a result of a failure in the fiber/matrix interface.…”

Mixed Mode I/II interlaminar fracture toughness of carbon Fiber/RTM‐6 laminates manufactured by VARTM

“…b[B]). This figure also shows the appearance of failure, wherein the exposed fibers are coated with a very thin layer of resin, which indicated that this specimen delamination crack propagated in the proximity of the interface fiber/resin (Fig. b[C]).…”

“…a[B], b[B], and c[B]). The shells are a surface fracture of polymeric matrix in concave form , In general, the cusps coalesce adjacent to the fiber plane and thus usually one surface will retain the cusps whilst the other will contain only the scars, called “scallops”. These morphologies appear when the cusps are separated from the fracture surface .…”

“…Therefore, the interlaminar fracture toughness characterization can be assisted by fractographic analysis of the fracture surface by scanning electron microscopy (SEM). The SEM analyses aids interpretation on the aspects generated in the fracture morphology, giving evidences on the type of stresses responsible for causing the failure, direction of cracks propagation, manufacturing defects and degradation by a combination of environmental factors . Therefore, a better understanding of carbon/epoxy composite fracture behavior within this temperature range is required.…”

Fractographic and rheological characterizations of CF/PP-PE-copolymer composites tested in tensile

“…This procedure is useful because it can be used to optimize the composite processing and also to prevent other damages that can occur in the future. Thus, fractographic studies have been strongly disseminated and used not only in the area of metallic materials, but also in the polymeric composites reinforced with continuous fibers [45][46][47][48][49][50][51][52][53] .…”