Experimental and numerical analyses of the tensile strength and mixed-mode fracture behavior of sheet molding compound plates

Abstract

Polymer matrix composites are the most prevalent among all composite materials because they offer a high specific strength-to-weight ratio, toughness, and ease of processing. These composites owe most of their properties to high-strength reinforcement materials, such as carbon, glass, and aramid fibers. The mass-production method for such composites is primarily sheet molding compound (SMC) compression molding. 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 the mechanical and fracture properties of such products. Therefore, in this work, the commercially available chopped-glass-fiber-reinforced polyester SMC has been subjected to uniaxial tensile and mixed-mode fracture experiments, both along and perpendicular to the rolling direction. The results of these experiments were used as input data in a finite element model to determine the fracture toughness (KIC and KIIC) and the critical strain energy release rates (GIC and GIIC) of the material under mixed-mode loading conditions. Overall, although the reinforcing material was glass fiber strands, SMC specimens exhibited lower mechanical properties and fracture toughness in the transverse direction than in the longitudinal (rolling) direction under all loading modes.