Bending fatigue behavior of twill fabric E-glass/epoxy composite

Twill E-glass/epoxy composite was considered for its bending fatigue behavior. Displacement controlled bending fatigue tests with stress ratio R of 0.1 were conducted on standard specimens and damage development in the composite was continuously monitored through the decrease of bending moment during cycling. The specimens were subjected to different fatigue loadings with the maximum loading level up to 75% of the material ultimate flexural strength. Early damage was observed after hundreds of loading cycles causing degradation of material stiffness with cycling. The amount of stiffness reduction was observed to be a function of the magnitude of the fatigue loading applied to the specimen. For some selected specimens, after 1 million cycles, fatigue tests were stopped and residual properties were measured. Different levels of reduction on material strength and elastic modulus were found to depend on the level of fatigue loading. Finally detailed discussion is made to correlate the found fatigue data and obtain general description of the material fatigue behavior useful for composite component design.