Press Release 15/2007

Tiny Avalanches

Software Developed by the KIT Reveals the Limits of Formability of Crystalline Metals
34973-1
Stochastic phenomena when bending a very thin wire

Dr. Elisabeth Zuber-Knost
Press Officer

Kaiserstraße 12
76131 Karlsruhe, Germany
Phone: +49 721/608-2089
Fax: +49 721/608-3658

Formability of metallic materials reaches its fundamental limits in smallest dimensions. An international team of researchers has discovered a universal distribution function for strain jumps occurring during deformation. The software to simulate the deformation behavior was developed by scientists of the KIT. The results were published in the renowned journal “Science” 318 (October 12, 2007, pp. 251).

For details, please contact:

Presse und Kommunikation
Universität Karlsruhe (TH)
Monika Landgraf

Phone: +49 721 608-8126
Fax: +49 721 608-3658
E-mail

Under mechanical loading, crystalline materials deform plastically. This irreversible deformation is attributed to the collective motion of lattice defects, so-called dislocations. They may be compared with minute avalanches: Deformation takes place in jumps. In conventional technical dimensions, it appears to be homogeneous. In small dimensions and microscopic components, however, this avalanche effect is reflected by strain jumps. A number of experiments carried out at the Forschungszentrum Karlsruhe confirmed these results.


Within the framework of the EU-funded international SizeDepEn (Size-dependent Engineering) cooperation, researchers from Karlsruhe, Budapest, Edinburgh, and Rome found an universal distribution function of these strain jumps by statistical analyses of the deformation behavior in experiment and simulation. This cooperation project was coordinated by the Institut für Zuverslässigkeit von Bauteilen und Systemen (izbs, Institute for the Reliability of Components and Systems) of the Universität Karlsruhe (TH).


The Karlsruhe researchers Dr. Daniel Weygand and Dr. Christian Motz from the izbs for the first time succeeded in reproducing this particular deformation behavior of crystalline metals by a discrete dislocation dynamics simulation.. “Similar distribution functions may also be applied to describe avalanches and earthquakes”, explains Weygand.


In metallic microstructures, these avalanche effects and their statistical distribution cause fundamental problems. When deforming a very thin wire, for instance, plastic deformation may distribute stochastically and the formation of a ring will become impossible. This might be a future challenge in the further miniaturization of micromechanical components.


The Karlsruhe Institute of Technology (KIT) represents the merger of the Universität Karlsruhe with the Forschungszentrum Karlsruhe. Altogether, it has 8000 employees and an annual budget of 600 million Euros. In the KIT, both partners are bundling their scientific competences and capacities, establishing optimum research structures, and developing joint strategies and visions.


The KIT will be an institution of internationally excellent research and teaching in natural and engineering sciences. KIT shall attract the best experts from all over the world, set new standards in teaching and promotion of young scientists, and establish the leading European center in the field of energy research. KIT will assume a leading role in nanosciences worldwide. It is the objective of KIT to be one of the most important cooperation partners of industry.


Monika Landgraf

Sequence of a stochastic simulation of the bending of a wire. From the top left to the bottom right, the diameter decreases from 100 μm to 0.1 μm. Stochastic simulation takes the now found frequency distribution of strain jumps into account. It is obvious that the formation of a ring becomes impossible with decreasing diameter due to the strong localization of deformation.

Photos of printing quality may be requested by e-mail or phone +49(0)721/608-2089.

lg, October 25, 2007
Contact:

 

Monika Landgraf
Head of Corporate Communications, Chief Press Officer
Phone: +49 721 608-41150
Fax: +49 721 608-43658
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Contact for this press release:

Monika Landgraf
Press Officer
Phone: +49 721 608-21150
Fax: +49 721 608-41150
monika landgrafTpj4∂kit edu