Characterisation of auxetic meta-materials for modelling and Simulation of new lightweight structures

• Applicants: Professor Dr.-Ing. Stefan Diebels; Professor Dr.-Ing. Hans-Georg Herrmann
• Subject Area: Mechanics
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 393104950

Within this project methods for new, auxetic microstructured materials shall be developed for lightweight design in order to replace conventional metallic materials. For this purpose, these auxetic structures have to be characterized and as a consequence new material models have to be defined for a FEM simulation. This project focusses on 2D-metal sheet structures as meta-materials. For a realistic simulation of the component material properties of these structures have to be known exactly. For this reason the mechanical properties of potential materials have to be experimentally analysed and described theoretically. Therefore a first aim of this project is to characterize the mechanical behavior of metallic materials with different microstructures by new adapted non-destructive methods.In a first step the mechanical behavior of 2D-metal sheet structures will be investigated. The development of the new material models will be based on extensive experimental investigations and on numeric homogenization strategies. As a result it will be shown which factors of the microstructure are significant to define the macroscopic material properties as auxetic. Based on this, elastic-plastic material models are developed for microstructured meta-materials, which can be used to describe the mechanical behavior of tray-like auxetic lightweight structures much better than previously.For this reason the suggested modelling will go far beyond the previous models and will include besides plastic effects additionally the anisotropy of typically auxetic materials. Furthermore, large deformations have to be considered for the material model. The implementation of the models into a finite-elements code allows a reliably predicting the mechanical behavior of auxetic metal sheet structures by means of numeric simulations. The experiments tests with 2D-metal sheet structures will be monitored with non-destructive methods of the LLB. For this purpose thermography will be enhanced and developed to correlate temperature variations to stress- and strain-conditions for elastic-plastic behavior. Using the digital Image Correlation (DIC) deformations of the component will be measured. By a specific combination of these two methods the specific advantages of each shall be used to reach an improved in situ characterization of the sample on micro and macro level. Furthermore, guided wave inspection with electromagnetic acoustic transducers (EMAT) will be applied in order to detect changes of the thickness during experiments. A further advantage of this method is the in situ characterization of materials properties during mechanical testing.

• DFG Programme: Research Grants