Correlation of statistical fatigue properties in a wide stress range for FRP laminates with failure mechanisms

The statistical aspect of fatigue properties in fiber-reinforced plastics is investigated. The P–S–N diagram was produced based upon the fatigue test results, which was conducted on the satin woven glass fabric/polyester laminate. The dependences of fatigue life and its dispersion on the applied stress level and fatigue frequency are discussed. The failure mode under fatigue loading mainly consisted of three kinds: the fiber breakage, matrix cracking and interlaminar delamination, which clearly depends upon the stress level, in other words, fatigue life region. The test results indicated that the wider scatter of the experimental data has been observed in the life range of 105–106 cycles. This characteristic can be well explained by the fact that there exist several dominant failure modes including delamination damage in this life region. The tension fatigue test results conducted on quasi-isotropic carbon/epoxy laminates, [0/±45/90]S, revealed that the dominant fatigue failure mode is a progressive delamination damage at −45/90 interlayer. The paper also discusses a concept for improving the fatigue resistance of a quasi-isotropic CFRP laminate as a result of suppressing the delamination damage.