Investigation of Mechanical Behavior of Chopped Carbon Fiber Reinforced Sheet Molding Compound (SMC) Composites

As an alternative lightweight material, chopped carbon fiber reinforced Sheet Molding Compound (SMC) composites, formed by compression molding, provide a new material for automotive applications. In the present study, the monotonic and fatigue behavior of chopped carbon fiber reinforced SMC is investigated. Tensile tests were conducted on coupons with three different gauge length, and size effect was observed on the fracture strength. Since the fiber bundle is randomly distributed in the SMC plaques, a digital image correlation (DIC) system was used to obtain the local modulus distribution along the gauge section for each coupon. It was found that there is a relationship between the local modulus distribution and the final fracture location under tensile loading. The fatigue behavior under tension-tension (R=0.1) and tension-compression (R=-1) has also been evaluated. Damage evolution on the free edge of the samples under cyclic loading has been recorded using optical microscopy by interrupting fatigue tests at different number of cycles. The results suggest that the interfacial failure between fiber and matrix is the dominant damage mechanism for SMC under fatigue loading.