Analysis of the cycle-mix effect on transverse cracking in glass/epoxy laminates under spectrum loadings

Fatigue tests were carried out on a glass/epoxy cross-ply laminate under Constant Amplitude (CA) and spectrum loading conditions. After the preliminary material characterization phase, the evolution of the total crack density with the number of cycles was analysed with tests at different load levels. Experimental evidence proved that the linear damage accumulation rule is not suitable in the case of spectrum loadings, leading to an underestimation of the real crack density evolution. This behaviour can be reconducted to the so-called cycle mix effect, which takes place when low-to-high stress changes occur.