Characterization of interfacial properties of composite materials by acoustic emission

The global mechanical properties of composite structures in service depend on fiber/matrix interface and interlaminar strength. The paper proposes to use Acoustic Emission (AE) and advanced signal processing to evaluate the i nterlaminar performance of polymeric composites. A delaminating process sim ulated with a Double Cantilever Beam (DCB) in opening mode (Mode I) coupled with an Acoustic Emission (AE) technique has been employed. Different samp les were analyzed to observe the damage evolution and to evaluate the inter laminar decohesion processes. The resistance to delamination growth is expr essed in terms of the interlaminar DCB mode (mode I) fracture toughness, me asured by strain energy release rate, G(I), dissipated per unit area of del amination growth in composite. Three categories of samples were used: two u nidirectional carbon fiber/epoxy resins with one degraded by heat and one w ith a commercially used resin. It was found that sample that was exposed at a temperature greater than the glass transition temperature Tg of the epox y had a higher cumulative energy release rate than the two other samples ty pes. The original type having the lowest release rate. Acoustic emission pa rameters have been found to be powerful indicators of the intensity of the damage. Multivariate analysis of up to 49 parameters was performed in order to group classes of AE signals with matching characteristics. A correlatio n was established between the energy release rate and the acoustic emission energy.