Experimental and numerical analyses of the tensile strength and mixed-mode fracture behavior of sheet molding compound plates
Applications of composite materials have been growing steadily over the last few decades and found their way in every product from household appliances to transportation vehicles and buildings. These materials are mainly classified based on the type of the matrix that holds other constituents all together, namely known as ceramic matrix, metal matrix, and polymer matrix composites. Among these materials, the polymer matrix composites are the most prevalent ones because they offer high toughness, specific strength to weight ratio, and ease of processing. These composites own most of their properties to the high-strength reinforcement materials as carbon, glass, and aramid fibers. The mass production method of such composites is basically the sheet molding compound (SMC) compression molding technology. However, regarding the inherent defects of SMCs, such as porosities and internal cracks, the current trend of improving their performance requires a thorough understanding of mechanical and fracture properties of such products. Therefore, in this work, the commercially available chopped glass-fiber reinforced polyester SMC have been subjected to a set of uniaxial tensile and mixed mode fracture experiments, along and perpendicular to the rolling direction. The results of these experiments were employed as input data in a finite element model to determine the fracture toughness (KIC and KIIC) and critical strain energy release rate (GIC and GIIC) of material under mixed mode loading conditions. Overall, although the reinforcing material were in the form of strands of glass fiber, SMC specimens exhibited lower mechanical properties and fracture toughness in transverse direction that the longitudinal direction (rolling direction of SMC plates) under all modes of loadings.