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Plastic Deformation Recovery in Freestanding Nanocrystalline Aluminum and Gold Thin Films

Submitted by Taher A Saif on
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Science 30 March 2007:
Vol. 315. no. 5820, pp. 1831 - 1834
DOI: 10.1126/science.1137580

Jagannathan Rajagopalan, Jong H. Han, M. Taher A. Saif*

In nanocrystalline metals, lack of intragranular dislocation sources leads to plastic deformation mechanisms that substantially differ from those in coarse-grained metals. However, irrespective of grain size, plastic deformation is considered irrecoverable. We show experimentally that plastically deformed nanocrystalline aluminum and gold films with grain sizes of 65 nanometers and 50 nanometers, respectively, recovered a substantial fraction (50 to 100%) of plastic strain after unloading. This recoverywas time dependent and was expedited at higher temperatures. Furthermore, the stress-strain characteristics during the next loading remained almost unchanged when strain recovery was complete.These observations in two dissimilar face-centered cubic metals suggest that strain recovery might be characteristic of other metals with similar grain sizes and crystalline packing.

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.

Self-healing polymers - an introduction

Submitted by Jinglei Yang on
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I'm now working on the preparation and characterization of self-healing polymers, a promising branch in materials science. The following is a general conception of this kind of materials system. (Pasted from our group website http://www.autonomic.uiuc.edu.) I may introduce some of my current work later.

Boundary Element Method for Hyperelastic Materials

Submitted by Mohsin Hamzah on
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I am interested in using the Boundary Element Method for the hyperelastic materials. The objective of this work  is to simulate the behaviour of elastomeric or rubber-like materials parts. I am now in the derivation stage, and I intened to use Ogden constitutive model with this derivation.

Ph.D. Studentships in Spacecraft Design, Dynamics and Control

Submitted by kdkumar on
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Ph.D. Studentships in Spacecraft Design
Dynamics and Control

The Department of Aerospace Engineering at Ryerson University has a strong and vibrant research programme involving the development of pico- and femto-satellites (weighing less than 1 kilogram) under Dr.

Characterization of myocardial viscoelastic behavior based on ventricular harmonic motion

Submitted by Arash_Kheradvar on
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Cardiac Mechanics

Our current ability to accurately measure ventricular global contractile behavior remains unsatisfactory due to the lack of quantitative diagnostic indexes that can assess the mechanical properties of myocardial tissue.

ELASTOMERS

Submitted by Mohsin Hamzah on
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Elastomers, or rubber like materials, have many engineering applications due to their wide availability and low cost. They are also used because of their excellent damping and energy absorption characteristics, flexibility, resiliency, long service life, ability to seal against moisture, heat, and pressure, and non-toxic. It can be easily molded into almost any shape. Applications of elastomers include solid propellant, biomechanics and medical/dental, tires, gaskets, and engine mounts.

A posteriori error estimation (indication) for extended finite element methods (XFEM)

Submitted by Stephane Bordas on
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Computational Mechanics Forum
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Extended finite element methods (XFEM) have been employed in computational fracture mechanics contexts since their inception in 1999. Although some work has been performed, leading to the first adaptive strategies for the generalised finite element method (GFEM), little or no work has been published on error estimation and adaptive approximations for XFEM. A first attempt at this challenging problem is published here: 

Thickness dependent critical strain in Cu films adherent to polymer substrate

Submitted by Rongmei niu on
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thin film
polymer

For the polymer-supported metal thin films that are finding increasing applications, the critical strain to nucleate microcracks ( εc ) should be more meaningful than the generally measured rupture strain. In this paper, we develop both electrical resistance method and microcrack analyzing method to determine εc of polymer-supported Cu films simply but precisely. Significant thickness dependence has been clearly revealed for εc of the polymer-supported Cu films, i.e., thinner is the film lower is εc . This dependence is suggested to cause by the constraint effect of refining grain size on the dislocation movability.

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