A Study on Flexure Behavior of AS4/914 Grade Carbon Fiber Reinforced Plastic Laminates under Static and Fatigue Loads

Flexure behavior of a carbon fiber reinforced plastic (CFRP) prepreg system, AS4/914, with five different layup sequences was investigated under static and fatigue loads to simulate typical loading geometry in an aircraft wing. The laminates were Unidirectional (UD), Cross Ply (CP), Angle Ply (AP), Laminate-1 (L1) and Laminate-2 (L2) with the layup sequences of [0/0](4S), [0/90](4S), [45/-45](5S), [0/45/-45/90](2S) and [0//90/45/-45](2S), respectively. The static behavior of the laminates were explained in terms of load-deflection curves, stress-strain curves and these behavioral aspects were compared with the analytical results obtained from the classical lamination theory (CLT). The highest strength with lowest deflection was observed for UD laminates, whereas AP laminates exhibited lowest strength with highest deflection. The CP laminate exhibited good strength, excellent deflection and progressive failure mechanism. The multilayered laminates L1 and L2 exhibited moderate strength. Stiffness degradation model was used to evaluate the progressive fatigue damage in these laminates at a particular load level. The fatigue damage results depicted that performance of L2 was superior in Stage 1, whereas, UD and CP gave steady state growth in Stage 2. The failure mode and the fracture features were evaluated through microstructural studies. A reasonably good correlation could be established between load-deflection curves and macroscopic features of the tested specimens.