Modeling and characterization of fatigue strength of laminated composites with knitted fabric reinforcement

Abstract

Results from both theoretical and experimental investigations on laminated epoxy composites reinforced with plain weft-knitted carbon fiber fabrics of different arrangements subjected to fatigue loads are presented in this paper. The stacking sequences used are [0/0/0/0], [0/45/-45/0], [90/90/90/90], [0/90/90/0], and [90/45/-45/90] where 0 refers to the fabric wale direction and 90 to the course direction. Tensile fatigue with stress control was applied to the laminates as well as to the monolithic matrix material, with a stress ratio of R = 0.1 and a cycling frequency of 5 Hz. The theoretical prediction for the laminate fatigue strength was made using a general methodology, which is a combination of the classical lamination theory and the bridging micromechanics model. The stresses sustained by each lamina layer in the laminate were determined according to the classical lamination theory, whereas the internal fatigue stresses generated in the fiber and matrix materials of the lamina were obtained by virtue of the bridging model. The internal stresses were detected against the constituent fatigue strengths at the similar loading conditions as applied to the laminate. Thus, the laminate fatigue strength was predicted only using the constituent fatigue data and the laminate geometric parameters, which were measured/determined independently. Reasonably good agreement has been found between the predicted and experimental S-N curves of all the five laminates.