A phenomenological experimental study was presented for understanding the effect of cyclic loading, generally experienced by typical modern aircraft structures during flight, on the propagation of micro-mesoscopic damage in carbon fibre reinforced composite laminates. Testing was carried out by employing ultra-high resolution SkyScan 1173 XRmicro computed tomography to identify and assess damage progression during fatigue testing. It provided qualitative as well as quantitative assessments of the damage in the composites which supported the analytical investigations.

An in-house solution was developed for statistically analyzing the occurrence, frequency and geometry of cracks throughout the fatigue life. This methodology was used to process the data from scan for the purposes of visualizing damage initiation and propagation. Hence, quantitative analysis could be performed. Analysis resulted in the definition of fatigue crack growth rates, da/dn for each of the 3 orthogonal planes, which was interpreted in terms of the 3 damage modes;​ opening, in-plane shear and out-of-plane shear. By applying linear elastic fracture mechanics (LEFM) laws, strain energy release rates were calculated, while differentiating between modes II and III in a novel manner.

For verifying the parameters obtained, definite cracks were traced and analyzed. Finally, a methodology was implemented to import the damage model into a finite element analysis (FEA) tool to be used for crack growth analysis, and simulations were compared to experimental findings.