Materials which get wider when pulled

FAU researchers are developing structures with completely new properties

The picture above shows the level by level blocks from auxetic material welded on top of each other; the graphic below shows the structure previously calculated in the computer. (Photo and graphics: EAM)

Experience tells us that the stronger an elastic band is stretched out, the narrower it becomes. Scientists at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) are looking at materials that react in exactly the opposite manner. They become wider when stretched and narrower when compressed. These new “auxetic” materials have useful mechanical properties. They can absorb a lot of energy or are especially tough and have a multitude of applications in practice: for example, in shock and sound absorbers or as bone substitute materials and implants in medical technology. Erlangen researchers in the lightweight construction and modelling fields of the Engineering of Advanced Materials Cluster of Excellence have designed and optimised these unusual structures. Furthermore, they report in two articles of the current issue of the journal, Advanced Materials: “Design of Auxetic Structures via Mathematical Optimization” by J. Schwerdtfeger, F. Wein, G. Leugering, R. F. Singer, C. Körner, M. Stingl and F. Schury (DOI: 10.1002/adma.201004090) and “Finding Auxetic Frameworks in Periodic Tessellations” by H. Mitschke, J. Schwerdtfeger, F. Schury, M. Stingl, C. Körner, R. F. Singer, V. Robins, K. Mecke and G. E. Schröder-Turk (DOI: 10.1002/adma.201100268).

Auxetic materials are physically characterised by a negative Poisson’s ratio, a size resulting from the mechanics or strength of materials, which describes the behaviour of a body under the influence of a tractive or compressive force. Their complex structures and geometries have been developed in interdisciplinary cluster projects in which mathematicians, physicists and material scientists are involved, through modelling and simulation first in the computer and then in a second stage produced using a rapid manufacturing process: selective electron beam melting. This is where a component is constructed from metal powder in layers using an electron beam through selective melting. A component produced in this way exhibits significantly improved mechanical properties, demonstrating a good correlation between calculated and measured mechanical properties. This illustrates the great potential for collaboration between scientists and engineers in the combination of physical modelling, mathematical structure optimisation and precision manufacturing.

In addition to the optimal design of auxetic cellular metals, modelling and simulation also play a crucial role in many other areas in the Erlangen Cluster of Excellence, such as in the field of computational chemistry or in the development of optical metamaterials at the nanoscale. The scientists report on their research work in 20 articles of the special issue “Hierarchical Structures Towards Functionality” of the journal, Advanced Materials, which is devoted entirely to the Engineering of Advanced Materials Cluster of Excellence. (The online edition can be found at

More than 60 scientists from all eight disciplines of the Cluster planned and wrote for the issue for over a year until the almost 200-page booklet was completed. It contains a variety of review articles from the material fields of nanoelectronics, optics and photonics, catalysis and lightweight design, which combine the aspects of the research done up to now in the Cluster of Excellence, as well as nine articles with new results published for the first time. “We are very proud, with this special issue of Advanced Materials, a world-leading specialist material science journal, to present our current research and work progress at an international and the highest scientific level. This is a very important testament to the outstanding performance of the Cluster of Excellence before its upcoming assessment for a second funding period from 2012 to 2017 and a unique feature of the Cluster,” says Professor Dr. Wolfgang Peukert, spokesman for the Engineering of Advanced Materials Cluster of Excellence and one of the three guest editors.

Further information for the media:

Prof. Dr. Wolfgang Peukert
Tel. 09131/85-29400

uni | media service | research No. 43/2011 on 13.9.2011

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