Damage evolution in cross-ply laminates under tension–compression and compression-compression cyclic loads

Tension-Compression and Compression-Compression fatigue tests were carried out on glass/epoxy cross-ply laminates, with different values of the minimum to maximum load ratio R (−1, −3, −5, −7, −10 and 20). During the tests, the damage evolution in the 90° ply was monitored at the macro-and micro-scales. Three damage scenarios were observed, depending on the load ratio: i) initiation and propagation of transverse cracks for R ≥ −3, ii) initiation of multiple inclined short cracks for R = 20, iii) a mixed damage type with the presence of both transverse cracks and inclined short cracks for −10 ≤ R ≤ −5. Finite Element analyses of micro-scale Representative Volume Elements, combined with a recently developed crack initiation criterion, revealed the role of the Local Hydrostatic Stress in the matrix in controlling the different damage scenarios. Eventually, quantitative analyses showed a highly detrimental effect of the compressive part of the cycle on the transverse crack initiation and propagation.