Experimental and numerical investigations of laminated, fibre reininforced plastics under crash loading

• Applicants: Professor Dr.-Ing. Christian Hopmann; Professorin Dr.-Ing. Stefanie Reese
• Subject Area: Polymeric and Biogenic Materials and Derived Composites
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 404502442

The dimensioning of carbon fibre reinforced plastics (CFRP) can achieve a high accuracy based on quasi-static material properties and material models for static loads. The use of CFRP in crash relevant applications requires the consideration of the strain rate dependency of the mechanical properties, which is particularly pronounced for polymer matrices. Known strain rate effects are for example the embrittlement and hardening at impact loading. Goal of the project is the generation of new findings in damage mechanisms and evolution in unidirectional reinforced CFRP (UD-CFRP) laminates under impact loading and their numerical representation on components scale. Additionally, the development of robust testing methods and an RVE serve the needs for reliable scientific results concerning strain rate dependent material properties.In this project, adequate test methods will be developed, which enable a reliable determination of the mechanical properties of UD-CFRP at crash relevant strain rates. The material behaviour under highly dynamic loading will be modelled and understood on this basis using a multiscale modelling approach.The input parameters for the material models will be determined from highly dynamic tests with neat resin und unidirectional reinforced specimens in the entire relevant strain rate spectrum. An existing drop weight tower will be used for this purpose, which requires the development of fixtures, specimen geometries and the adaptation of suitable measurement instrumentations.A representative volume element (RVE) incorporating fibre, matrix and the interface will be used to investigate the material behaviour on the micro scale. This RVE provides on the one hand knowledge in strain rate effects and, on the other hand, its suitability for the numerical generation of mechanical properties will be investigated. Furthermore, a continuum mechanical description of UD-CFRP is aspired to represent the strain rate dependent, anisotropic material behaviour on the meso scale. The representation of plasticity and damage evolution is a key aspect here. Based on this, a macro model will be set up, which uses the mentioned continuum mechanical model. Investigations of the delamination behaviour of laminates under impact loading are used to develop a finite element formulation, which includes multiple laminate layers and also the consideration of delamination effects in a single element. A validation of the macro model will be performed with numerical and experimental investigations of a demonstrator part.

• DFG Programme: Research Grants