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Pradeep Sharma's picture

Revisiting Quantum Notions of Stress

I plan to submit the attached paper on quantum mechanical definition of stress in the next few weeks. Comments and feedback are welcome. Fair amount of work has been done on stress definition in the context of classical molecular dynamics (also attracting some controversies). In contrast, there appear to be several open issues in the quantum case. Hopefully, the attached paper provides a starting point.

tadmor's picture

Multiscale Postdocs at Minnesota

Several postdoc positions are available immediately at the University of Minnesota to work on the development of a variety of cutting edge multiscale methods and atomistic simulation techniques.  The work will be done in close collaboration with a group of leaders in the field including Prof. Ellad Tadmor, Prof. Richard James, Prof. Mitchell Luskin and Prof. Ryan Elliott.  For more information, visit www.multiscale.umn.edu or check out the attached announcement.

Jean H. Prevost's picture

Postdoctoral position at Princeton University

Postdoctoral position available at Princeton University to participate in a multi-disciplinary research project sponsored by the US Army Research Office (ARO/MURI) at Princeton and Harvard Universities on: Innovative Design of Multi-Functional Adaptive Structural Materials. The candidate will be involved in the Modeling of Hierarchically Porous Material Structures Optimized for Strength and Transport. The candidate must have a strong background in Finite Element Analysis (both solid and fluid), and in Topology Optimization.

3rd International Conference on Mechanics of Biomaterials & Tissues - program now available!

Program for the 3rd International Conference on Mechanics of Biomaterials & Tissues now available at http://www.icmobt.elsevier.com/programme09.htm

Plenary and keynote speakers include:

Professor Julian Vincent, Professor of Biomimetics, Bath University, UK
-Stiffness and toughness of biological materials

Free Online Mechanics of Materials Textbook

I have posted the second edition of my book “Mechanics of Materials” online for free educational use. The book was reviewed and checked for accuracy by 30 faculty across the USA and was line edited by a professional editor.

The preface in the book describes the objectives and the design of the book, with details elaborated further in “Note to the Instructor”. The “Note to the Students” elaborates the many pedagogical features of the book. All these are in the file labeled “Table of content and front end material”.

Harold S. Park's picture

USNCTAM 2010: Minisymposium on Mechanics of Crystalline Nanostructures

Horacio Espinosa and I welcome the submission of new abstracts for a minisymposium on "Mechanics of Crystalline Nanostructures", to be held at the 2010 US National Congress on Theoretical and Applied Mechanics (USNCTAM 2010), June 27-July 2 at Penn State University. 

softening, weakening and localization

Hello, everyone

I am a little confused about the discrimination between softening, weakening and localization.

In my opinion, softening is against hardening, corresponding to the decrease of slope in the hardening curve.

weakening is for what?

Localization is about localized plastic flow. 

localization is a phenomenon that explain the softening, so "localization" can not give help for better simulation result. Is that coreect?

 Thanks for correcting the views above!

Constitutuive modelling of viscoelastic materials

I am currently working on constictutive modelling of soft biological tissues, considering them as nonlinear viscoelastic materials. I am using the split form of energy density function i.e modelling separately the hyperelastc part and the visoelastic part. I am using Ogden formula for hyperelastic part and for the viscoelastic part, I am currently using the second and third invariants of stretch rate tensor.

asit_rathod1's picture

Relation Between Et(tangent Modules) & Es(secant Modules) in non linear elastic plastic theory?

dear all

            is there any formaula or any theory by i can make a relation for the tangent and secent modules in the plastic region of the stress strain curve?....and also how to find Et and Es for the Alloy steel?.. if any body knows any thing than let me know soon..

warm regards

Asit Rathod

Prestigious 5 year Fellowship -- RAEng/EPSRC Research Fellowships

To all outstanding researchers with less than 3 years of post-doctoral experience, this is a unique opportunity to secure a 5 year post-doc.

This will be highly competitive, and applicants must be of world-class quality. 

Topics available in our group:

- multiscale (fracture) mechanics

- microstructurally-faithful modelling

- surgical simulation

Markus J. Buehler's picture

Postdoctoral Associate position available at MIT

A postdoctoral associate position at MIT is available immediately, in the broad area of atomistic, molecular and multi-scale modeling of hierarchical biological, bioinspired and nanostructured materials. Material properties of specific interest include mechanical properties, in particular deformation and failure mechanisms. The work will emphasize on mutable properties (mechanomutability, thermomutability) and the analysis and design of adaptive, responsive, and robust materials through the integration of scales, from nano to macro. 

Stress invariants

This is a very fundmantal question.

What is the physical significance of stress invariants?

I understand that the stress invariant J2 of the deviatoric stress tensor is used to ecpress the yield criteria-but this is same as Von Mises yield criteria-I want to know what is so special about-stess invariants?

I understand that these invariants remain unaltered by rotation/transformation of the axis-is this the only reason for being so special or there i any other reason as well?

marco.paggi's picture

Anybody knows a molecular dynamics software for Windows operative systems?

 

Dear All,

I am looking for a freeware molecular dynamics software working for Windows operative systems.

I have tried LAMMPS, but it seems to me that it works only under UNIX. 

Thank you very much in advance for any information.

Best wishes, Marco Paggi 

_____________________________________

Jidong Zhao's picture

Postdoc position at HKUST on computational mechanics/geomechanics

A post-doc position is available now for one who has recently obtained (or about to get) his/her PhD on computational
geomechanics or computational mechanics. The successful candidate is expected to have strong background of mechanics
and extensive experience on computer programming (e.g., coding in FEM and/or DEM), and is able to work independently.
He/she who has previously worked on multi-scale modeling of material behavior will be particularly welcome to apply. The
initial contract is one year and is extendable to multiple years subject to his/her performance and availability of funding.

Geometric factor for mode II stress intensity factor for a finite strip under under pure shear loading

The geometric factor for mode I stress intensity factor for a finite strip under pure tensile loading is reported in Tada handbook as F(a/h) = 1.122 - 0.231(a/h) + 10.55*(a/h)^2 - 21.71*(a/h)^3 + 30.382*(a/h)^4 , but in the existing literature, I could not find such geometric factor for mode II stress intensity factor for a finite strip under under pure shear loading. Does anyone know such geometric factor for mode II stress intensity factor for a finite strip under under pure shear loading, if it is reported in the existing literature? or, if it is available in any unpublished sources?

FEA Improves Reliability of Flip-Chip Packaging

On Aug 10, 2009, Semiconductor International (SI) Newsbreak published a report on my work in AMD about 3D fracture study of underfill delamination as the top story in that issue.  I have never imagined that. Except the pleasure I received from this good news, I wonder if this work is also interesting to iMechanica community.  For that reason, I attach here the SI news report and the original paper published on ITherm2008 Proceedings. Welcome any comments and thoughts.

Horacio Espinosa's picture

PhD Dissertation Positions in Nanomechanics at Northwestern University

Description
Applications are invited for graduate studies within the Micro and Nano Mechanics Laboratory in the Department of Mechanical Engineering, Northwestern University.  The successful candidate will join a vibrant interdisciplinary research group and be involved in projects addressing atomic scale experimentation and modeling of advanced materials.  We seek motivated, talented and independent individuals interested in pursuing a PhD in one of the following areas:
•    Mechanics of Graphene and applications

Cai Shengqiang's picture

A theory of constrained swelling of a pH-sensitive hydrogel

Many engineering devices and natural phenomena involve gels that swell under the constraint of hard materials. The constraint causes a field of stress in a gel, and often makes the swelling inhomogeneous even when the gel reaches a state of equilibrium. To analyze inhomogeneous swelling of a pH-sensitive gel, we implement a finite element method in the commercial software ABAQUS.  The program is attached here.  Contact Shenqiang Cai (shqcai@gmail.com) for a description of the program.

Dear Omid and Sepehr

I think a non-zero entry in the stiffness matrix doesn't necessarily imply dependence of ith DOF on the jth DOF. This is the case also for standard FEM (without any enrichments). For example for a quadrilateral 2D element the x component of displacement has interaction with y component at each node, but as we know, two independent values of translation in x and y directions can

what is the proof of vector addition of forces

what is the proof of vector addition of forces, actully how two vectors are added acccording to triangle parellelogram laws , actully i know the process but what is the source or origin of that rule who devised that and how please tell!

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