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Amit Acharya's picture

Fracture and singularities of the mass-density gradient field

A continuum mechanical theory of fracture without singular fields is proposed. The primary
contribution is the rationalization of the structure of a `law of motion' for crack-tips, essentially
as a kinematical consequence and involving topological characteristics. Questions of compatibility
arising from the kinematics of the model are explored. The thermodynamic driving force
for crack-tip motion in solids of arbitrary constitution is a natural consequence of the model.
The governing equations represent a new class of pattern-forming equations.

mohsenzaeem's picture

Effects of SiC, SiO2and CNTs nanoadditives on the properties of porous alumina-zirconia ceramics produced by a hybrid freeze casting-space holder method

Highly porous alumina-zirconia ceramics were produced by adding space-holder materials during freeze casting. To increase the strength of porous ceramics, different amounts of nanoadditives (silicon carbide-SiC, silica-SiO2, and multi-wall carbon nanotubes-CNTs) were added. Space-holder materials were removed by preheating, and solid samples were produced by sintering. Up to 68% porosity was achieved when 40% space-holder was added to the solid load of slurry. Wall thicknesses between pores were more uniform and thinner when nanoadditives were added.

FastBEM Fracture 2-D available for download

The fast boundary element program used in the recent paper:

Y. J. Liu, Y. X. Li, and W. Xie, "Modeling of multiple crack propagation in 2-D elastic solids by the fast multipole boundary element method,"  Engineering Fracture Mechanics, 172, 1-16 (2017)

Faxin Li's picture

A breakthrough in Guided Wave – Excitation of shear-horizontal (SH) wave is not a problem any longer

Excitation of non-dispersive shear-horizontal (SH) waves in plates is always a challenge. Recently, we successfully excited single-mode SH0 wave in plates using a face-shear (d24) mode piezoelectric transducer. Meanwhile, the d24 mode transducer can selectively receive SH0 wave and filter Lamb waves. This work was published as a Letter in the IOP journal Smart Materials and Structures (http://dx.doi.org/10.1088/0964-1726/25/11/11LT01).

Fatemeh Ahmadpoor's picture

A perspective on the statistical mechanics of 2D materials

2D materials are fascinating for numerous reasons. Their geometrical and mechanical characteristics along with other associated physical properties have opened up fascinating new application avenues ranging from electronics, energy harvesting, biological systems among others. Due to the 2D nature of these materials, they are known for their unusual flexibility and the ability to sustain large curvature deformations. Further, they undergo noticeable thermal fluctuations at room temperature.

Ajeet Kumar's picture

Unusual couplings in elastic tubes - negative poisson effect and overwinding on being stretched

We demonstrate intersting extension-torsion-inflation coupling in intrinsically twisted chiral tubes. In particular, we show that by tuning its intrinsic twist and the material constants, such tubes can show negative poison effect on being stretched. Similarly, such tubes can overwind initially when stretched - the same unusual behavior has been reported earlier when a DNA molecule is stretched. See the attached paper which will appear soon in the Journal of Elasticity.

zichen's picture

Edge effect of strained bilayer nanofilms for tunable multistability and actuation

Inspired by the need to develop reconfigurable materials at the micro- and nano- scales that are capable of exhibiting more than one stable configuration, we employed both theoretical and computational models supported by experiments to study the multistable behavior of a Si/Cr microclaw and uncover the mechanical principles involved.

trisha_sain's picture

Phd positions in Michigan Technological University

PhD positions are available from Fall 2017, in Michigan Technological University, in Mechanical Engineering-Engineering Mechanics Department. The candidates are to work in the computational modeling of multiphysics behavior of polymer materials, high rate fracture response of gel like tissue mimicking materials or Design of microarchitectured polymer composites for improved functionality. Interested candidates can email their CV with relevant information at -tsain[AT]mtu.edu

Candidates with background in continuum mechanics, finite elements and materials modeling are preferred.

Timothy Morrissey's picture

A Transparent, Self-Healing, Highly Stretchable Ionic Conductor

Self-healing materials can repair damage caused by mechanical wear, thereby extending lifetime of devices. Here, a transparent, self-healing, highly stretchable ionic conductor is presented that autonomously heals after experiencing severe mechanical damage.

A Transparent, Self-Healing, Highly Stretchable Ionic Conductor

Christopher Provatidis's picture

CAD-based precursors of IsoGeometric Analysis

Article title: CAD-based collocation eigenanalysis of 2-D elastic structures
Journal title: Computers and Structures
Author: Dr. C Provatidis
Final version published online: 18-Dec-2016
DOI information: 10.1016/j.compstruc.2016.11.

Bin Liu's picture

The widely used tensile stiffness ratio is not a correct measure of anisotropy degree

In our recent paper, some interesting conclusions are found when we attempt to establish a standardized compliance matrices for general anisotropic materials. The abstract is as follows.

UMAT for isotropic hardening

Choose a channel featured in the header of iMechanica: 

 

Hello,

I'm new here and I'm not sure if this a right place to ask a question or not.

I'm trying to practice writing UMAT code and I just finished the (Coding for isotropic Mises plasticity) from the the attached document. I'm trying to check validity of this code with simple model: what kind of this simple model? how can I do that? 

 

Please help me with this problem

Regards,

Qusay

Chiqun Zhang's picture

On the relevance of generalized disclinations in defect mechanics

Chiqun Zhang            Amit Acharya

The utility of the notion of generalized disclinations in materials science is discussed within the physical context of modeling interfacial and bulk line defects like defected grain and phase boundaries, dislocations and disclinations. The Burgers vector of a disclination dipole in linear elasticity is derived, clearly demonstrating the equivalence of its stress field to that of an edge dislocation. We also prove that the inverse deformation/displacement jump of a defect line is independent of the cut-surface when its g.disclination strength vanishes. An explicit formula for the displacement jump of a single localized composite defect line in terms of given g.disclination and dislocation strengths is deduced based on the Weingarten theorem for g.disclination theory at finite deformation. The Burgers vector of a g.disclination dipole at finite deformation is also derived.

Arash_Yavari's picture

On the Stress Field of a Nonlinear Elastic Solid Torus with a Toroidal Inclusion

In this paper we analyze the stress field of a solid torus made of an incompressible isotropic solid with a toroidal inclusion that is concentric with the solid torus and has a uniform distribution of pure dilatational finite eigenstrains. We use a perturbation analysis and calculate the residual stresses to the first order in the thinness ratio (the ratio of the radius of the generating circle and the overall radius of the solid torus). In particular, we show that the stress field inside the inclusion is not uniform.

International Conference ECCOMAS SMART 2017, Madrid, Spain, on smart materials

Within the frame of the 8th ECCOMAS Thematic Conference on Smart Structures and Materials (SMART 2017), to be held in Madrid, Spain, on June 5-8, 2017, we are organizing minisymposium MS13 titled “Smart materials capable of recoverable inelastic strain”. 

Relevant contributions are solicited specifically in the following technical areas:

mesarovic's picture

Special Issue: Granular materials; Journal: Materials

Journal: Materials  (flyer attached)

Impact Factor 2.728

Special Issue: Granular materials   Special Issue Editor: Sinisa Mesarovi       Deadline: 15 April 2017

D. Schulte's picture

Wissenschaftlicher MA - Numerische Mechanik (FEM) -

Am Institut für Kontinuumsmechanik der Leibniz Universität Hannover ist eine Stelle als

"Wissenschaftliche Mitarbeiterin / Wissenschaftlicher Mitarbeiter" - EntgGr. 13 TV-L, 100 % - zum nächstmöglichen Zeitpunkt zu besetzen.
Die Stelle ist auf 4 Jahre befristet.

Zhengjin WANG 王正锦's picture

Extrusion, slide, and rupture of an elastomeric seal

Elastomeric seals are essential to two great technological advances in oilfields:  horizontal drilling and hydraulic fracturing.  This paper describes a method to study elastomeric seals by using the pressure-extrusion curve (i.e., the relation between the drop of pressure across a seal and the volume of extrusion of the elastomer).  Emphasis is placed on a common mode of failure found in oilfields:  leak caused by a crack across the length of a long seal.  We obtain an analytical solution of large elastic deformation, which is analogous to the Poiseuille flow of viscous liquids.

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