Influence of Fabric Architecture on Damage Progression Evidenced by Acoustic Emission Measurements

Previous experimental results have studied the effect of fabric architecture on the static and fatigue response of glass reinforced polymer composites. Additional studies have analyzed the acoustic emission (AE) signatures of glass/epoxy composites which are monotonically loaded to failure [1-3]. These studies have identified systematic testing methodologies, and general relationships between measured acoustic properties and specific internal damage modes. The primary acoustic emission property utilized within this work is the peak frequency of each acoustic event. A plot of this peak frequency as a function of the applied strain show distinct levels, or bands, often attributed to specific damage modes, e.g., matrix cracking, interphase failure etc. Common fiberglass fabrics utilized within wind turbine blades have heavy unidirectional fibers held in place with stitching, a layer of random mat, or a combination of both. Results presented within this paper include the acoustic emission results for unidirectional composites monotonically loaded in both longitudinal and transverse directions, and biaxial composites from the same fabric. These results are compared with acoustic emission frequencies from glass/epoxy pre-preg materials with no stitching or additional backing material. It is shown that the addition of plies at different orientations and the removal of stitching effect the number of acoustic events and the strain to failure.