Dorr, Nicolas

The development of lightweight structures is a complex and interdisciplinary process that inte-grates the fields of design, materials science, and manufacturing engineering. Increasing re-quirements due to e-mobility influence the subcomponents of the chassis directly - higher loads and demands for such lightweight structures with unchanged cost pressure. Hybrid structures were proven to be effective within this context. In the state of the art, different metal-plastic hybrids are presented. The objective of this work is to further advance such hybrid systems by substituting steel with a unidirectional glass-fiber-reinforced thermoset (UD-GFRP). Owing to its high specific strain energy and simultaneously high strength, UD-GFRP is well suited for load-path-optimized structural components. How-ever, the introduction of load transfer elements into such structures is both complex and often accompanied by a reduction in structural performance. By combining the continuously fiber-reinforced thermoset carrier structure with thermoplastic injection-molded material to form a hybrid component, these disadvantages can be largely mitigated. Nevertheless, research gaps remain with respect to the interfacial adhesion of thermoplastic–thermoset hybrids and the influence of surface pretreatment methods. The combination of dissimilar materials in a hybrid structure inherently leads to residual stresses due to differences between the curing or bonding temperature 𝑇𝐻 and the operating temperature 𝑇𝐸. These residual stresses may result in a reduction of the overall bond strength within the hybrid system. For thermoset–thermoplastic hybrids, thermally induced residual stresses have so far only been insufficiently investigated. The intrinsic hybrid structure developed in this work – consisting of a thermoset serving as a stiffening element and a thermoplastic serving as a load introduction element – is designed for application in highly loaded components. The development focuses on three main aspects: First, the bond between thermoset and thermoplastic is examined with particular attention to the adhesion mechanisms and potential methods for their improvement. The second part of the study investigates the residual stresses arising during the thermal manufacturing process are investigated, which result from the mismatch in the coefficients of thermal expansion of the constituent materials. In the final part, the interaction within the hybrid composite is examined using an application-oriented demonstrator. Specifically, it is assessed whether residual stresses can be relieved and how this affects the demonstrator’s service life. Based on the findings, a recommendation for an optimal interface between the thermoplastic and thermoset materials will be provided. Finally, a recommendation is derived for an optimized interface de-sign between thermoplastic and thermoset materials.

Nicolas Dorr

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