Characterisation of auxetic meta-materials for modelling and Simulation of new lightweight structures
Final Report Abstract
In this project, the focus was on the investigation and mechanical characterization of auxetic structures made from 2D sheet structures of an aluminum alloy. The main goal was to gain a comprehensive understanding of the behavior of this special class of mechanical metamaterials to optimize their application possibilities in lightweight construction. Auxetic materials are characterized by a negative Poisson’s ratio, which allows for expansion perpendicular to the direction of tensile stress, unlike conventional materials that constrict under tensile load. This unique property, combined with reduced density and improved mechanical properties such as increased shear modulus and energy absorption capacity, makes auxetic materials a promising alternative for use in new lightweight constructions. The characterization of the auxetic structures was carried out through uniaxial and biaxial tensile tests. These were supplemented by the development of an innovative in-situ testing system that combines digital image correlation (DIC) and thermography to precisely capture both the local strain state and temperature changes due to plasticization processes. A key result of this project was the development of an elasto-plastic material model capable of simulating the complex behavior of auxetic structures under various loading conditions. The successful identification of a suitable representative volume element (RVE) allowed the upscaling of the auxetic structure for simulating with lower calculation time. Furthermore, additional non-destructive testing methods were applied to further analyze the deformation behavior and specific properties of the auxetic structures. Thermoelastic stress analysis enabled the localization and quantification of tensile and compressive stresses on the sample surface. Computed tomography and radiography allowed for a detailed examination of changes in sheet thickness and the state of deformation, while high-frequency ultrasound measurements provided further valuable insights into the mechanically induced changes in the structures. In summary, this project has provided fundamental insights into the behavior and properties of auxetic structures. The results, especially the developed material model and the obtained mechanical properties, form a solid basis for the application of these materials in future lightweight constructions and open up new paths for the design and optimization of metamaterials.
Publications
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Experimental and Theoretical Investigations of Auxetic Sheet Metal. Advanced Structured Materials, 689-707. Springer International Publishing.
Gordanshekan, Arash; Heib, Tobias; Ripplinger, Wolfgang; Herrmann, Hans-Georg & Diebels, Stefan
