Strength degradation due to fatigue-induced matrix cracking in FRP composites: An acoustic emission predictive model

Assessment of strength degradation in unidirectional Gl/Ep [90]7 composite specimens, due to fatigue-induced matrix cracking, is herein performed using acoustic emission data recorded during a static proof-loading. To address a generalized problem, coupons were subjected to constant amplitude sinusoidal loading of R = 0.1, R = −1 and R = 10 stress ratio. In each case, several stress level and life fraction combinations were interrogated. An engineering model, introduced in a previous work, was implemented. The model, based on a conventional acoustic emission descriptor, predicted tensile strength degradation after constant or variable amplitude fatigue. Although established and validated on [±45]S specimens undergone tensile R = 0.1 constant amplitude loading, the scheme also proved applicable in the [90]7 coupon configuration, under all R-ratios examined. More important, both tensile and compressive residual strength was predicted. With the principal damage mode in all cases being matrix cracking, model performance in coupon residual strength estimation was remarkable.