Strength and Modulus Degradation of Carbon Fiber-Reinforced Polymer Laminates from Fiber Misalignment

Fiber-reinforced polymer (FRP) laminates are being used as external reinforcement for strengthening concrete members. The performance of unidirectional FRP laminates is highly dependent on fiber orientation with respect to applied load direction. In the case of fabrication by manual layup, it is possible to have fiber plies installed with improper orientation. In this project, the degradation of strength and modulus of carbon FRP laminates from fiber misalignment was investigated experimentally using tensile coupons. The specimens consisted of one and two plies of unidirectional carbon FRP impregnated with a two-component epoxy. The misalignment angles varied from 0 to 40° for the one-ply samples, and from 0 to 90° for one ply of the two-ply samples. The size effect on the strength and modulus was investigated for one-ply specimens with misalignments of 5 and 10°. For these specimens, the ply width was maintained constant and the length was varied so that the aspect ratio ranged between 2 and 8. It was concluded that misalignment affects strength more than elastic modulus. However, provided that mechanical parameters are related to the crosssectional area of laminate with fibers continuous from end to end of the coupon, the degradation of strength can be accounted with a knock-down factor that is independent of misalignment angle.