Fatigue damage characterization and percolation in plain-weave carbon fiber-epoxy composites

The concept of ‘damaged unit cell’ was employed to describe the tensile fatigue damage evolution in plain-weave carbon-epoxy composites. The fatigue damage was connected to the development of cluster of damaged unit cells and their distribution, considering the measurements by thermoelastic damage analysis (TDA). Internal damage state was also observed by SEM. The experimental results showed that the size ratio of the maximum damaged unit cell cluster, Cmax, rapidly increased after the damaged unit cell ratio p exceeded 0.527, called ‘percolation threshold’ pc. This threshold announced the fatigue final failure, which occurred with fast accumulation of transverse cracks, wider local delamination and fibers breakage, once p exceeded pc. Since the relationship between the averaged thermoelastic damage response and Cmax was nearly linear, the fatigue damage evolution involved clustering of damaged unit cells. The fractal dimension D of the damaged unit cells cluster increased up to a steady state value Dc, when p exceeded pc, showing the faster fatigue damage evolution. Finally, the fatigue damage evolution was predicted using the concept of percolation and mutual interference between damaged units. •Thermal analysis of the tensile fatigue damage evolution in a plain-weave composite.•The cluster of damaged unit cells had a peculiar percolation threshold.•Estimation of fractal dimension of the damaged unit cells cluster.•Prediction of fatigue damage evolution considering the interaction of damaged units.