Hollow glass spheres in sheet molding compound composites: Limitations and potential

Abstract

AbstractSheet molding compounds (SMC) are commonly used in automotive applications as they lead to increased fuel efficiency of vehicles due to their high strength to weight ratios. This study focuses on understanding the effect of replacing calcium carbonate (CaCO3) with hollow glass spheres (HGS) in an unsaturated polyester resin matrix SMC composite with the ultimate goal to further reduce density without compromising performance. The resulting glass fiber (GF)‐reinforced syntactic foam laminate composites with GF content ranging from 10 to 15 vol% have densities of 1.2 and 1 g/cm3, respectively. This is significantly lower than the industry standard SMC density of 1.9 g/cm3. The HGS parameters of interest are primarily HGS type (S28HS and S32HS), loading level (33–44 vol%), and surface functionalization (methacrylsilane). The syntactic foam composites were characterized in terms of tensile, flexural, and impact properties, and their properties were compared to those of standard density SMC. As expected, the flexural, tensile, and impact properties were compromised with a decrease of density. However, they were higher than the corresponding properties of low‐ and ultra‐low density composites reported in the literature, as we were able to add higher GF content in these low‐density SMC formulations. It was also concluded that methacrylsilanized surface treated HGS showed promise in maintaining the mechanical properties, especially at high sphere loadings. The impact energy of the low‐density formulations was relatively unaffected by HGS type or loading.