Interlaminar shear fatigue behavior of glass/epoxy and carbon/epoxy composites

This work addresses a strong need in accurate fatigue properties of glass- and carbon-fiber reinforced polymer-matrix composites. In particular, interlaminar shear fatigue properties of glass/epoxy and carbon/epoxy composite tape material systems used in aircraft fatigue-critical applications are needed. The interlaminar shear fatigue material properties, essential for the development of the analysis methods able to capture fatigue delamination failure onset in composite structures, are presented in this work. S-N curves are generated based on custom short-beam shear (SBS) fatigue tests. The custom SBS test configurations ensure a consistent interlaminar shear failure mode. This work extends the recently developed methodology, published in Composites Science and Technology to characterize nonlinear shear properties of composite materials using digital image correlation (DIC) and finite element analysis, to fatigue loading. Test data sets used to develop the fatigue properties, include approximately 20 glass/epoxy and 30 carbon/epoxy SBS coupons. All tests were run in load control at 0.1 load ratio. To better understand material behavior under cyclic loading, surface shear strain was monitored using the DIC technique. Accurate shear stress approximation resulted in similar S-N curve shapes for the glass-fiber and the carbon-fiber composites.