A fracture mechanics approach using Acoustic Emission Technique to investigate damage evolution in woven-ply thermoplastic structures at temperatures higher than glass transition temperature

By means of a fracture mechanics-based approach, this work was aimed at investigating the damage evolution in 5-harness satin weave carbon fabrics reinforced PolyPhenylene Sulphide (PPS) structures at T > Tg (glass transition temperature) when matrix toughness is significantly enhanced. Structures with a quasi-isotropic stacking sequence and a single-edge-notch geometry are characterized by an elastic-brittle response resulting from transverse matrix cracking and fibers breakage near the notch tip. Acoustic Emission (AE) activity is associated with these primary damage mechanisms, and the monitoring of AE signals is particularly relevant as it provides a reliable approach to quantify the strain energy release rate GI as a function of the cumulative acoustic energy WAE. In order to examine the correlation between AE energy and fracture energy, the coefficients of the model have been identified from the set of experimental data for one given ratio aw. It therefore appears that the cumulative AE energy can be used as a damage criterion to determine the damage tolerance (through the evaluation of fracture energy) of a thermoplastic-based composite material. In addition, the definition of a macroscopic damage variable based on stiffness measurements and the evolution of the cumulative AE events may be used to investigate the fracture sequence and the damage kinetics. A power law independent from the loading conditions can be identified, and therefore be used to assess the severity of damage during loading. Finally, the correspondence in damage evolution given by the experimental AE data at microscopic scale and a cumulated damage variable at macroscopic scale validates the ability of both approaches to quantify the damage degree in fiber-reinforced PMCs, and to identify a critical threshold for damage initiation.