Abstract

The idea of material modeling in the realm of injection-molded composites is to predict the macroscopic behavior of the material from the mechanics and physics at the microscopic level, which, in turn, are related to the details of the underlying injection process. An efficient way of predicting the microstructure's influence on the overall properties is the mean-field homogenization approach, adequate in a wide range of practical applications. Therefore, the anisotropic elasto-plastic stiffness, thermal properties, material strengths can be then directly computed as a function of the local average fiber orientation and of additional variables, such as fiber volume fraction and temperature, and can be made available for the remaining finite element simulation. Thus, in our implementation, the needed material data in the shape of a variable material response can then be transferred to other simulation environments and combined with the information on the local microstructure determined from third party simulation tools or real experimental data: this process enables us to realize accurate hierarchical multiscale and multiphysics simulations of fiber reinforced plastic components. This work discusses our approach, its benefits, and illustrates its practical and important application for the analysis of a servo-assisted automotive steering system, whose injection molded housing is made of short-fiber reinforced glass-fiber composite. In fact, since the limit of 95 g/km for CO2 emissions came into effect in the EU zone, lightweight structural design and components made of short fiber reinforced plastics started playing a central role for manufacturers of original equipment in the automotive industry. To meet such stringent requirements, a steering housing made of 50% weight glass-fiber-reinforced polyamide and manufactured through injection molding was developed at thyssenkrupp Presta AG and analyzed with the help of our new multiscale tools dedicated to short fiber composites. Multiscale modeling tools were critical in this important design and assessment phase while looking for a lighter material to be used for the housing and conferring the structure a higher (or at least the same) structural strength than that obtained with the previous metal.