Sheet Molding Compounds: Testing, virtualization and hybridization

Abstract

Driven by the new European regulations in terms of vehicle¿s CO2 emissions reductions, every new Internal Combustion Vehicle (ICV) and novel Hybrid and Electric vehicles (HEV) manufacturer is being pushed to search innovative and new technologies. In this situation, lightweighting is still a key factor to consider for facing the short-driving-range issue and new Noise Vibration and Harshness (NVH) requirements of HEVs, and for decreasing fuel consumption for ICVs. To overcome these new challenges, the implementation of lightweight polymeric composites is an interesting alternative to be considered. In this field, Sheet Molding Compounds (SMC), a type of short fiber reinforced composites (SFRP), present an interesting balance of high thermomechanical performance, design and molding freedom, and cost-competitiveness at mid- large-scale productions. This Thesis aims to advance on several aspects of the product development process of SMC, for improving their process simulation and bring this closer to industry, to better understand the thermomechanical performance of SMC at high temperatures, and to add advanced functionalities in terms of enhanced vibration damping properties to ease their application in HEV applications. For this, first, different viscosity characterization techniques have been analyzed and the influence of the obtained experimental results on the subsequent viscosity model calibration for compression molding simulations were studied. Then, the anisotropic thermomechanical performance and failure mechanisms have been stated at room and high temperatures, and lastly, the hybridization of SMCs with Thermoplastic Elastomers (TPEs) for improving their structural damping characteristics was explored. The obtained results pointed out the potential of standard rheological equipment in front of dedicated academic instruments for robust, easy-to-generate, and industrially implementable viscosity measurements. Besides, these techniques enabled fast and reliable viscosity model calibrations for compression molding simulation tools. Furthermore, the influence of temperature in the anisotropic mechanical performance and failure, revealed, how the anisotropy of the material and the underlying failure mechanisms are changed by this environmental variable. Finally, the generation of hybrid bi-material SMC-TPE structures in the shape of sandwich assemblies, allowed to improve and customize the vibration damping performance of SMCs. In conclusion, this Thesis opens new possibilities to implement SMC materials in the current and future transport industry by strengthening the product development process of them.