Failure prediction of graphite/epoxy laminates with induced intermittent load surge during fatigue

Experimental Study of Fatigue Characteristics of Laminated Composite Plates

“…The correlation between the stiffness degradation rate and the loading parameter is described as power function dependence; this model divides the S-N curve of the fiber reinforced polymer composite into three regions, the first region approaches a nearly horizontal line where the number of cycles to failure depends more on statistical strength distribution than the stress level, the second region is more classical fatigue behavior where the S-N correlation can be describe as a power low function and the third region suggest a fatigue limit where an infinite lifetime is found below a given stress or strain level -the fatigue strength. [Diawekar 2002] produced an analytical model supported by numerical simulation which describes the behavior of the energy release of composite materials subjected to the fatigue, this model established that accumulation of damage due to intermittent surge in applied load reduces the energy release rate ((G)) of the material . The effect of constant amplitude, regularly applied overloads to the energy release rate of [0/90]n graphite/epoxy composite appears diminished as the structural integrity reduces over time suggesting the effect of the overloads is more severe during the initiation of delamination growth, their investigation shed light on the nature and extent of damage accumulation during spectral fatigue.…”