Damage development in open-hole composite specimens in fatigue. Part 1: Experimental investigation

Interrupted fatigue tests were carried out with peak amplitude at 60% of the ultimate static load (60% severity) in order to determine the 3D sequence of damage events using X-ray Computed Tomography (CT). Matrix cracking at the surface ply and initiation of matrix cracks in the subsequent plies lead to delaminations that progress through the thickness, and ultimately to the propagation of delamination at the −45/0 interface all the way back towards the end tabs. The log (number of cycles to failure) decreased linearly as the maximum fatigue stress level increased.