A postdoctoral position at Sandia National Labs in Livermore, CA is available for an applied mechanics engineer with a strong background in computational constitutive model development. The work will support our current projects in the areas of continuum plasticity and failure modeling. The applicant will also be expected to implement models into Sandia computer codes for high-performance computing simulations. In addition, the candidate will collaborate with structural analysts to apply these advanced models to Sandia applications.

I am using exponent Drucker-Prager model at the moment, is there anyone can tell me where the follow exponent D-P eqation comes from originally?

(σ e)(σ e)=λ(σt)(σt)-3(λ-1)σmσt

Where λ= is hydrostatic stress sensitivity parameter and equal to σc/σt, σe is effective stress, σm is hydrostatic stress, σc, σt are stresses under compression and tension, respectively.

A postdoctoral position is available starting Fall 2008 in the area of computational solid mechanics. A successful candidate is expected to have a strong background in multiscale modeling and programming experience. While experience in plasticity using finite element methods or dislocation dynamics is a plus , all outstanding candidates will be considered.

Applicants must provide a detailed resume and  at least three references to: Prof. Marisol Koslowski, marisol@purdue.edu.

Our topic is a continuation of the May 15 discussion led by Professor Julia Greer on “Experimental Mechanics at Nano-scale”.  The whole story about the “micro-pillars” started in 2004, when Mike Uchic et al. used focused ion beams (FIB) to make micro-pillars from pure Ni and Ni alloys that can then be uni-axially compressed by a flattened AFM tip [Science 305, 986-989, 2004].  The flow stress is found to increase with decreasing sample diameter even though there is no imposed strain gradient as in micro-indentation, bending or torsion experiments.  This finding generated a lot of excitement worldwide. 

Currently, i am now attempting to establish a plasticity/damage coupling model using continuum damage mechanics for complex metal structures such as steel pressure vessel, which can be implemented using finite element analysis. The model can predict the progressive failure and damage evolution as well as the crack initiation and propogation due to large plastic deformation of metal structures. Who can give me some suggestion or idea?

I was awarded my PhD in Structures and Materials Mechanics from Ecole Nationale des Ponts et Chaussées (France). My thesis focused on the nonlinear  dynamics of cracked turbines rotors (please see attached abstract) and was done at the Mechanical Solids Laboratory of Ecole Polytechnique. The Thesis (in french) could be downloaded at http://pastel.paristech.org/1793/.

In Computational mechanics, for rate(time) dependent calculations (eg. Creep, plasticity), when we say time step dt, does it mean physical time.

Can I think this way:

I start at time 0 and calculate stress, strain etc  after 1 sec, 2 sec, 3 sec..

Also, what exactly is strain rate? why do some books say ..'when a strain rate is applied'''..I'm confused..dont we just apply displacement or force all the time.

Does it mean that..the expression of strain rate gives how the strain evolves with time...(eg; In creep, under constant load, how the strain evolves with time)

Kindly throw somelight on these..I'm new to computational mechanics..

Harikrishna 

kfupm.edu.sa/publications/ajse/articles/3318_P.18.pdf

Based on much experimental and theoretical work in the last decade or so, mechanical properties of materials at nano-scale are proving to significantly deviate from their bulk counterparts. This is true not only for nano-structureD materials (i.e. composed of nano-scale components like nanocrystalline materials) but also for nano structureS (surface-dominated structures like carbon nanotubes (CNT’s), nanowires, etc.). Nanoindentation has been a very effective and well-characterized technique for determination of hardness, modulus, and stiffness, and for crystalline materials the indentation hardness has been widely shown to be significantly higher at shallower indentation depths (so-called indentation size effect, or ISE). However, inserting a sharp indenter tip into a material inevitably sets up strong strain gradients in the deforming volume, which is often linked to the origin of the ISE. Moreover, the infinitesimal volumes probed via this technique are coherent with the remaining matrix, rendering the effects of free surfaces on mechanical properties inaccessible.

The Computational Solid Mechanics group under the direction of Prof. Marisol Koslowski in the School of Mechanical Engineering at Purdue has an opening for a postdoctoral position in the area of multiscale modeling as part of the project “Plasticity in ultrafine grained materials” funded by DOE. A successful candidate is expected to have a strong background in computational solid mechanics and programming experience. While experience in plasticity using dislocation dynamics or phase field methods is a plus, all outstanding candidates will be considered.

Does anyone know of a simple book, approximately 50 pages or so, for plasticity?. I am looking for something that is similar to Morton Gurtin's "Topics in Finite Elasticty" published by SIAM. This book is an uncluttered treatment of finite deformation elasticity and was very useful for me during graduate work. I am NOT looking for 200-300 page texts, becasue I will never get around to reading them.

 -Amit 

 doi:10.1016/j.jmps.2007.03.009

http://dx.doi.org/10.1016/j.ijfatigue.2008.03.004

Hi, everyone

I just start my research on bounding surface model for soil mechanics. Does someone have documents about programming of bounding surface model for stress-strain behaviour with a piece of program? Thanks a lot for your help.

Hi everybody,

 i?m simulating a manufacturing chain finite elements analysis. Every step of this chain have been developed by different software. I use ANSYS. Somoone know how to impose the initial strain and stress state deriving from previous simulations to my ansys model: I'm able to use INISTATE command but only stresses are imported, I loose initial strain info: are they important if my material is elasto plastic? how i can resolve the problem?

Thanks in Advance Michele

I'm leaving the US in a couple of days and will probably take a hiatus of a few months from iMechanica.  Before I leave, I want to tell you about a C++ idiom that eases the implementation and use of multiple material models in a computational mechanics code.

The first book on C++ idioms was by Jim Copilien sometime in the late 1990s called "Advanced C++: Programming Styles and Idioms".  The idea of such idioms has become considerably widespread since then - so much so that there is a Wikibook on the subject .

Hi everybody,

I am a phD student modelling the behaviour of the ceramics under nanoindentation using ABAQUS. I have read that Drucker Prager plasticity model is suitable for ceramics under indentation. To obtain these parameters ABAQUS users manual suggest doing a triaxial test, but I can not find any information relating triaxial test with ceramics (I only find it for soils and rock). Does anybody know another way  to obtain these parameters? Has anybody performed this test experimentally before?

 Thanks,

 Iratxe

Dear all,

Do you have any reference about the theory of plasticity? Especially about flow theory and von Mises yield criterion?

For example if I have an effective stress - plastic strain relationship, and I after yielding, I increase my strain again, how can I obtain the increment of the plastic strain and the stress deviator tensor?

Thanks a lot.

Best,

Ray

I noticed that the Rodney Hill Prize in Solid Mechanics has been founded and would like to have his personal records in detail, hopefully with his portrait(photo). 

hi everybody.

 I am interested to implement  tresca failure criteria in my plastic material model (ABAQUS/standard) using UMAT subrountine which is avaiable in ABAQUS code but it is primaryly made for Mises failure , so i made few attempt to modified it for tresca , but it did not work out, so if anyone have any idea , please guide me. 

thanks

prashant sharma 

A field theory of dislocation mechanics and plasticity is illustrated through new results at the nano, meso, and macro scales. Specifically, dislocation nucleation, the occurrence of wave-type response in quasi-static plasticity, and a jump condition at material interfaces and its implications for analysis of deformation localization are discussed.

We are pleased to announce Dislocations 2008, an international conference on the fundamentals of plastic deformation and other physical phenomena where the dislocations play pivotal roles.  The conference will take place on October 13-17, 2008 at the Gold Coast Hotel, Hong Kong, China.  More information about the Dislocations 2008 conference can be found at the following web site:

Professor Jose E. Andrade from Northwestern University is the
recipient of the 2006 Zienkiewicz medal awarded biennially by the
Institution of Civil Engineers from London. The award goes to Andrade
for his contribution entitled ' Capturing strain localization in dense
sands with random density' in IJNME 2006; 67:1531-1564 DOI:
10.1002/nme.1673 (link: http://www3.interscience.wiley.com/cgi-bin/fulltext/112519037/PDFSTART)

Our sincerest congratulations to Prof. Andrade!