Advances in sheet molding compounds for automotive applications

Abstract

This master thesis addresses new approaches in the manufacturing of lightweight composites for the automotive industry. Governmental regulatory and customer requirements force car manufacturers to reduce the weight of new car models on an ongoing basis. Therefore, the goal of this thesis was to find new techniques to create lightweight sheet molding compound (SMC) composites for automotive applications. Two general approaches were chosen: 1) Investigating basalt fibers as an alternative reinforcement to the commonly used glass fibers and 2) light-weighting of SMC composites by replacing a portion of the heavy reinforcing fibers with a small amount of cellulose nano-crystals (CNC). An SMC production line similar to the ones used in industry was used to make the various SMC sheets. The composites were then made by compression molding of the SMC and were characterized using various characterization techniques, e.g. single fiber fragmentation test, differential scanning calorimetry, thermo-/mechanical testing and microscopy. In the first part of the study, it was found that SMC composites made with basalt fibers show overall similar properties to those made with glass fiber reinforced composites. The advantage of basalt fibers is that they are an ecofriendly and lower cost alternative to glass fibers. The second part of the study showed that adding small amounts of CNC can enhance the mechanical properties of glass fiber reinforced SMC composites significantly, allowing to reduce the fiber content leading thus to a weight reduction of 11%.