Nano Letters 9, 2295 (2009), 10.1021/nl9004805, http://www.rsc.org/chemistryworld/News/2009/May/26050903.asp, http://www.nytimes.com/2009/07/07/science/07obsalt.html, http://www.sciencenews.org/view/generic/id/45132/title/Salt_stretches_in..., http://www.sandia.gov/LabNews/090605.html, http://www.newscientist.com/article/dn17374-salt-crystals-reveal-surpris..., http://www.youtube.com/watch?v=OGcFCD8E7o8

I am currently running a Quasi-Static compression simulation in Abaqus Explicit using the Johnson-Cook Plasticity option. As the strain gets beyond the elastic range, the stress-strain response begins to oscillate +- 5 MPa around the expected curve. Does anyone know why this is happening and/or how to repair the problem?

Thanks, 

D. Barrett Hardin

Dear Mechanical Engineers,

It's my pleasure to be one of your group. I have a question in Abaqus Explicit and all my friends recommended me to as iMechanica as the explicit Abaqus is more popular to you than us as civil engineers.

Does anyone knows where I can find any paper discuss the existence of potential functinoal for materials that violate the maximum plastic dissipation principle (due to non-convex yield function and/or non-associately fluw rule)?

Hi

this is Probal from university of western ontario (UWO). I am working on three roller flow forming process and i have to model the deformation specially in the splined area. could you please give me any idea or give any link so that i can have an idea what to do.

thank you probal 

In joint material interface between elastic and elastic-plastic material, how can we show the continuity of displacement theoretically?It must be continuous and compatible of deformation in practical case.Could anyone help me to understand this answer?

There will be a mini-symposium entitled "Defects and Microstructure at the Nanoscale and Beyond," at the USNCCM-10 conference in Columbus, OH, July 16 -19, 2009.  This topic is of keen interest to the I-Mechanica community and we hope many of you will join us there. Our goal is to bring together researchers from the mechanics, materials, and physics communities to cross-fertilize research on defect-mediated processes in microstructural evolution, with a focus on both hard and soft materials. 

Hello,

hello everybody.

ı am looking for relationship between shore D and shore A.Not a curve i need chart.I would be appreciated if you send me this diagram.I have some hypolon and PU roll .I am using  shoremeter  to see the hardness .

if you have you may send  violetlover@mynet.com

have a nice day

gökhan

Recently, we do some work about the dynamic strain aging. In order to investigate the function of solute clouds and precipitates in DSA, we do some experiments. The solution treated LY12 alloys are tested on MTS at low temperature (173K), and the Portevin-Le Chatelier phenomenon disappeared as we expected. But, we need more information about the change of microstructure under the low temperature, what is more the micro-optical observation should be finished in a very short time when we consider the effect of natural aging. Obviously the TEM can not meet our needs.

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?

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