Acoustic emission analysis and micro-mechanical interpretation of mode i fracture toughness tests on composite materials

Abstract Mode I fracture toughness tests on Double Cantilever Beam specimens from carbon-fibre and glassfibre reinforced polymer-matrix composites were monitored with Acoustic Emission (AE) and loaddisplacement traces and delamination lengths were recorded. AE characterized the kinetics of delamination propagation. The progress of AE activity and AE intensity with load and AE source location plots are used to determine the delamination onset on the microscopic and macroscopic scale. Energy dissipating processes initiated in the damage zone near the delamination tip. Low interface adhesion results in lower debonding stresses and larger damage zones compared with composites with good adhesion. Time-dependent linear location of AE sources yields the average length of the damage zone and the average speed of delamination propagation. Parameter analysis has been used empirically for identifying AE source mechanisms. A new classification software for transient AE waveforms permits identification of the source mechanism of individual AE signals. A micro-mechanical fracture model based on the AE results describes the contributions of microscopic matrix and interface mechanisms to the interlaminar fracture energy.