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

在本项目中，应开发新的拉胀微结构材料的轻量化设计方法，以取代传统的金属材料。为此目的，这些拉胀结构的特点，因此，新的材料模型必须被定义为有限元模拟。该项目的重点是二维金属板材结构作为元材料。为了真实地模拟这些结构的部件材料特性，必须准确地知道。因此，潜在材料的机械性能必须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适应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。新材料模型的开发将基于广泛的实验研究和数值均匀化策略。因此，它将显示哪些因素的微观结构是显着的宏观材料性能定义为拉胀。在此基础上，建立了微结构超材料的弹塑性模型，该模型能够更好地描述托盘状拉胀轻质结构的力学行为，不仅考虑了典型拉胀材料的塑性效应，还考虑了其各向异性。此外，材料模型必须考虑大变形。将模型实施为有限元代码允许通过数值模拟可靠地预测拉胀金属板结构的机械行为。二维金属板结构的实验测试将采用LLB的非破坏性方法进行监测。为此目的，将加强和发展热成像技术，以使温度变化与弹塑性行为的应力和应变条件相关联。将使用数字图像相关（DIC）测量组件的变形。通过这两种方法的特定组合，应使用每种方法的特定优点，以在微观和宏观层面上实现样品的改进的原位表征。此外，将采用电磁超声换能器（EMAT）进行导波检查，以检测实验期间厚度的变化。该方法的另一个优点是在机械测试过程中原位表征材料性能。

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.