Analysis and evaluation of the effects of residual stresses on the damage evolution in intrinsically manufactured hybrid materials under static and cyclic loading

• Applicants: Professor Dr.-Ing. Thomas Niendorf; Professor Dr. Thomas Tröster
• Subject Area: Polymeric and Biogenic Materials and Derived Composites ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 399304816

Decrease of vehicles weight through lightweight design is a suitable approach to promote resource and fuel efficiency in the automotive sector. Due to their weight-specific high strength and stiffness, modern vehicle concepts increasingly make use of fiber-reinforced plastics (FRPs). Besides the solitary use of these FRP composites, application of hybrid structures in highly loaded parts of the vehicle is feasible. Time and cost efficient production of those hybrid structures can be realized by process induced bonding of metal and FRP. Such kind of intrinsic hybridization allows to significantly reduce the total number of processing steps. However, the interface between metal and FRP is the weakest link in these hybrids, as the different thermal expansion coefficients of fiber and metal lead to the evolution of residual stress upon cooling from processing temperature to room temperature. At critical areas of the component, these stresses can be relieved through localized delamination.In the first funding period of the project, residual stress states in intrinsically manufactured plastic-metal layered hybrid composites were investigated in depth. So far, the main focus was particularly on methodological questions concerning the experimental residual stress determination in layered composites. Furthermore, the effects of materials and process parameters on the resulting residual stress distributions were assessed. Multi-scale approaches using established simulation methods were developed and implemented for in-depth understanding of relevant phenomena. In the second funding period, the effects of manufacturing-induced residual stresses on the behavior of hybrid materials under mechanical loading will be studied. Damage evolution under static and cyclic loading will be in focus of these investigations. Additionally, relationships between residual stresses, defects and structural integrity will be established. With respect to the envisaged applications of hybrid material composites, effects of active fiber pre-stressing on the damage evolution are to be investigated in particular, taking the residual stress state into account.The analytical methods applied in the project will allow for the determination of the influence of residual stress on the damage behavior under mechanical (static and cyclic) loading. Moreover, the results obtained will be used to establish a knowledge base which, after completion of the project, will allow to avoid unfavourable residual stress states and promote favourable ones to be set through targeted parameter selection during production. Eventually, based on the investigations, a reliable and safe use of hybrid material composites in the envisaged fields of application will be ensured.

• DFG Programme: Research Grants