In‐situ acoustic emission monitoring during electron microscopy of a model composite system

Abstract

AbstractThree‐point‐bend testing of a continuous unidirectional glass reinforced unsaturated polyester composite was chosen as a model to study the acoustic emission (AE) response and associated damage events in composite materials. Conventional three‐point‐bend samples were tested over a wide range of span‐to‐depth ratios, with failure modes established by post‐failure scanning electron microscope (SEM) analysis. In addition, in‐situ AE monitoring with simultaneous SEM recording was undertaken during three‐point‐bend testing inside an SEM vacuum chamber. These two test methods, using different equipment and sample geometry, were found to yield similar mechanical and AE results. The in‐situ tests enabled the development of the various stages of damage to be observed while the AE response was simultaneously monitored. This enabled the AE signals to be unambiguously assigned to specific damage accumulation mechanisms. It was concluded that the AE amplitude distribution can be divided into three main ranges in this system: 60 to 65 dB, 75 to 85 dB, and larger than 90 dB corresponding to matrix damage, fiber‐matrix debonding, and fiber breakage, respectively. It has been demonstrated that the coupling of AE monitoring with SEM recording of a composite system undergoing mechanical loading is a very powerful technique in the study of damage accumulation in advanced composite materials.