Abstract
Effects of variable fatigue loading with alternate R-ratios on fatigue life of a quasi-isotropic woven fabric CFRP laminate have been studied. Variable R-ratio fatigue tests are carried out in which the stress ratio of fatigue loading alternates between two values that are associated with the same number of cycles to failure. The fatigue life of the composite under variable R-ratio loading is examined not only for different pairs of stress ratios, but also for different constant values of fatigue life. By comparing the fatigue lives under constant and variable R-ratio fatigue loading conditions, the effect of alternation in R-ratio on fatigue life of the CFRP laminate is elucidated. Finally, prediction of fatigue life of the CFRP laminate subjected to the alternate R-ratio loading is attempted using a linear cumulative fatigue damage rule in conjunction with the anisomorphic constant life diagram by which the fatigue lives of component constant amplitude fatigue loadings are evaluated. It is demonstrated that the linear damage accumulation rule predict fatigue lives of the CFRP laminate for the alternate R-ratio fatigue loading with an accuracy of a factor of two.
