Fractography of Composite Materials

Abstract

The advent of composite materials and the knowledge acquired in the recent years in this area has increased the performance of the aeronautical industries' products. As the structural applications for fiber‐reinforced polymeric composites continue to increase, so too does the need for a thorough understanding of the fundamental failure processes in the different materials systems. To understand the mechanisms governing the behavior and failure processes of fiber‐reinforced plastics composites, it is necessary to know the origin and subsequent development of specific fracture features. With this knowledge, the mode of fracture, the overall direction of crack propagation, and ultimately the origin and sequence of structural failure may be ascertained. The study of fracture surfaces or fractography as it is more commonly known has been applied to continuous fiber‐reinforced plastics (CFRP), for over 20 years, and much work has been done during this time. But more is needed if a fundamental understanding and a database of the mechanisms and characteristics of fracture for different composite systems are to be established. In this article, the fracture behavior of carbon fiber‐reinforced thermoplastic and thermosetting polymer composites was evaluated as a result of fracture under different environmental conditioning and mechanical tests. Fatigue, longitudinal and transversal tension, compression, and “short beam shear test” were carried out. Tests were conducted at different temperatures (from—55 to 80°C) under various percentages of moisture‐absorbed contents (totally dry to saturated condition). A fractographic analysis was made to help in the understanding of the failure mode and reveals by the analysis of the fracture surface, the dominant mode of failure in every temperature‐moisture content pair for each mechanical test. The main issue of this work is the use of fractography to understand the relation between the environmental conditioning, the mechanical test, the degradation of the composite (interface, matrix degradation), and the fracture surface.