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Plasticity

Weixu Zhang's picture

Effect of surface energy on the yield strength of nanoporous materials

This is a very rough manuscript but including the original material we used. Any criticism or suggestion is welcome. The only aim of this letter is to reflect the multi-effect of surface energy on material or structure in nanosize scale. Here we report the effect of surface energy on the yield strength of nanoporous materials. The conventional micromechanics method is extended to consider the surface effect and expression of effective yield surface of nanoporous materials in complex stress state is derived.

ES 246 Project: Saint-Venant Torsion Problem

I plan to explore the Saint-Venant torsion problem applied to prismatic bars with elastic-plastic behavior. Wagner and Gruttmann have developed a finite element method to obtain the elastic/plastic stresses of a bar using a single load step. In particular, I will present the constitutive model that they have developed, and then use ABAQUS to apply Wagner and Gruttmann’s model to various cross-sections.

Xuanhe Zhao's picture

ES 246 project: Planar Composite under Plastic Deformation

The mechanical performance of a homogeneous material can be varied by the addition of second-phase particles. In this project, we will model a planar composite under plastic deformation. As shown on the following figure, the composite consists of matrix material and randomly-distributed inclusion particles. The matrix is assumed to be an elastic-plastic material with isotropic or kinematic hardenings, and the inclusion particle pure elastic with a higher Young’s modulus. The stress/strain field throughout the composite will be calculated numerically with finite element method.

Nanshu Lu's picture

ES 246 project: Plane Strain Extrusion - Slip-line Field Solution vs. FEM Solution

Due to maturity of FEM package, slip-line field theory is not widely used these days. However, we shall keep in mind that slip-line field analysis can provide analytical solutions to a number of very difficult problem which may involve huge deformations or velocity discontinuities, e.g. many metal forming processes. To evaluate these two analytical and numerical methods for plasticity I will try a simple example, compare these two solutions and finally get into a conclusion of my own.

Kristin M. Myers's picture

ES 246 Project: Large Deformation Plasticity of Amorphous Solids, with Application and Implementation into Abaqus

node/add/imageI propose to investigate an elastic-viscoplastic constitutive model proposed by Anand and Gurtin [1] for the large deformation of amorphous solids.  Specifically, I will present the constitutive framework proposed for elastic-plastic amorphous materials, I will implement the constitutive equations into Abaqus/Explicit, and I will compare numerical results with experimental results for polycarbonate [2]. 

 

Liu's picture

Void-induced strain localization at interfaces

We published this paper in APL on a study of the deformation near interfaces. It provides insight in the strain localization at the interface and its influence on the deformation in bulk metals. 

Abstract An optical full-field strain mapping technique has been used to provide direct evidence for the existence of a highly localized strain at the interface of stacked Nb/Nb bilayers during the compression tests loaded normal to the interface. No such strain localization is found in the bulk Nb away from the interface. The strain localization at the interfaces is due to a high void fraction resulting from the rough surfaces of Nb in contact, which prevents the extension of deformation bands in bulk Nb crossing the interface, while no distinguished feature from the stress-strain curve is detected.

Joost Vlassak's picture

Plastic deformation of freestanding thin films: Experiments and modeling

This is a paper we recently published in JMPS on a study of the mechanical properties on thin films comparing experimental results with discrete dislocation simulations. It provides insight in the strengthening that occurs in thin metal films when surface or interface effects become important.

The abstract is below; the full paper can be downloaded from here

Abstract - Experimental measurements and computational results for the evolution of plastic deformation in freestanding thin films are compared. In the experiments, the stress–strain response of two sets of Cu films is determined in the plane-strain bulge test. One set of samples consists of electroplated Cu films, while the other set is sputter-deposited. Unpassivated films, films passivated on one side and films passivated on both sides are considered. The calculations are carried out within a two-dimensional plane strain framework with the dislocations modeled as line singularities in an isotropic elastic solid. The film is modeled by a unit cell consisting of eight grains, each of which has three slip systems. The film is initially free of dislocations which then nucleate from a specified distribution of Frank–Read sources. The grain boundaries and any film-passivation layer interfaces are taken to be impenetrable to dislocations. Both the experiments and the computations show: (i) a flow strength for the passivated films that is greater than for the unpassivated films and (ii) hysteresis and a Bauschinger effect that increases with increasing pre-strain for passivated films, while for unpassivated films hysteresis and a Bauschinger effect are small or absent. Furthermore, the experimental measurements and computational results for the 0.2% offset yield strength stress, and the evolution of hysteresis and of the Bauschinger effect are in good quantitative agreement.

Joost Vlassak's picture

ES 246 projects

Each student creates a project that addresses a phenomenon or issue in plasticity theory, and presents it in class after the winter break. The scope of the projects is very wide: experimental, computational, or a critical discussion of one or more papers. The project contributes 30% of the grade, distributed as follows:

  • 5%: November 30 Thursday. Post your project proposal in iMechanica.
  1. Title. ES 246 project: e.g. Plastic buckling of plates.
  2. Tags. Use the following tags: ES 246, plasticity, Fall 2006, project
  3. Body. (i) Describe the project. (ii) Cite at least 1 journal article.
  • 5%: December 7 Thursday. Post a comment to critique the project proposal of at least 1 classmate.
Horacio Espinosa's picture

The 13th International Conference on Experimental Mechanics

Dear Colleagues:

The 13th International Conference on Experimental Mechanics (ICEM13, http://www.icem13.gr) will be held on July 1-6, 2007 in Alexandroupolis, Greece. It is our pleasure to announce that the Conference will include a special symposium organized by us entitled, “Plasticity, Fracture and Fatigue at the Micro and Nano Scales,” which will focus on recent developments in this area within the larger scope of assessing research needs in a variety of applications of interest.

Egon Orowan

August 2, 1901 — August 3, 1989
By F. R. N. Nabarro and A. S. Argon

in Biographical Memoirs v70, 1996

Prepared as a Biographical Memoir for the Royal Society of London and the U.S. National Academy of Sciences.

 

EGON OROWAN died in the Mount Auburn Hospital in Cambridge, Massachusetts, on 3 August 1989, a day after his 87th birthday. He is buried in the Mount Auburn Cemetery. Together with G.I. Taylor and Michael Polanyi, he was responsible for the introduction of the crystal dislocation into physics as the essential mediator of plastic deformation. Though he occasionally spoke at meetings concerned with science and technology policy, and wrote letters to the press on a number of topics, he was an essentially private person and left no biographical notes. In compiling the present Memoir, FRNN has been principally responsible for the period 1902-1951, which Orowan spent mainly in Europe, and ASA for the period 1951-1989, when Orowan was affiliated with the Massachusetts Institute of Technology.

Taxonomy upgrade extras: 

Egon Orowan

August 2, 1901 - August 3, 1989

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