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

在这个项目中，为了取代传统的金属材料，应该开发新的、非塑性微结构材料的轻量化设计方法。为此，必须对这些结构进行表征，因此必须为有限元模拟定义新的材料模型。这个项目的重点是2d金属板结构作为超材料。为了真实地模拟这些结构的组成材料的性质，必须准确地知道。因此，必须对潜在材料的力学性能进行实验分析和理论描述。因此，本项目的首要目标是通过新的非破坏性方法来表征具有不同微观结构的金属材料的力学行为。在第一步的力学行为的2d金属板结构将进行研究。新材料模型的发展将基于广泛的实验研究和数值均匀化策略。结果表明，哪些微观结构因素对确定材料的宏观性能具有重要意义。在此基础上，建立了微结构超材料的弹塑性材料模型，该模型可以较好地描述盘状辅助轻量化结构的力学行为。由于这个原因，建议的模型将远远超出以前的模型，除了塑性效应之外，还将包括典型的非塑性材料的各向异性。此外，必须考虑材料模型的大变形。将这些模型转化为有限元程序，可以通过数值模拟可靠地预测金属板结构的力学行为。二维金属薄板结构的实验测试将采用LLB的非破坏性方法进行监测。为此，热成像技术将得到加强和发展，以将温度变化与弹塑性行为的应力和应变条件联系起来。利用数字图像相关（DIC）测量元件的变形。通过这两种方法的特定组合，各应使用的特定优势达到了样品在微观和宏观水平上的原位表征。此外，将利用电磁声换能器（EMAT）进行导波检测，以检测实验过程中厚度的变化。这种方法的另一个优点是在机械测试过程中对材料性能进行现场表征。

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.