Once in a while I have to find the stiffness of a spring that I get from the local hardware shop.  I usually use a formula that can be found in some books on mechanics of materials.

But the assumptions bother me a bit because the springs that I used usually underwent large deformations and I wasn't sure whether the numbers I was using were correct or not.  

To check the formula I compared its predicted k to numbers from Abaqus simulations and found reasonably good results for many situations - but not for soft springs.

I've attached a write-up on that that contains a python script to generate the geometry.  Let me know if you find it useful.

I've recently had the opportunity to take another look at plasticity in the large deformation context.  I've avoided going into geometric and other issues involved with multiplicative deformations (points stressed in earlier blog posts by Giovanni (http://imechanica.org/node/11545), Arash (http://imechanica.org/node/11623)  and Xiabo (http://imechanica.org/node/11599).  Attached are some old notes that I'd prepared some years ago to help me with the details.  I hope they're of use to other students of mechanics.

-- Biswajit

Please find attached a report on a comparison between ANSYS SHELL181 and SOLSH190 elements with particular emphasis on applicability to linear elastic sandwich panels.

Title: Comparison of Ansys elements Shell181 and Solsh190

Abstract:

Prof. Rebecca Brannon and her team have created a wonderful page containing interesting information on aspects of plasticity, damage, and computational mechanics (particularly, the Material Point Method).

Check it out at 

 http://csm.mech.utah.edu/content/

-- Biswajit

From http://sydney.edu.au/news/physics/1737.html?newsstoryid=6425

VALE Nicolae Nicorovici 1944-2010By Professor Ross McPhedran

11 February 2011

Dr Nicolae Alexandru Nicorovici was born in Bucharest Rumania in the last year of World War II. He completed his education at the University of Bucharest with a PhD in Atomic Physics, dealing with the relation between interaction cross-sections and unitary symmetries. He then worked for the Rumanian Atomic Energy Commission, specialising in computation and theoretical physics.

In 2010,  Yves-Patrick Pellegrini published a paper in Physical Review B called

 Dynamic Peierls-Nabarro equations for elastically isotropic crystals.  with the abstract

Every year I try to get funding for things that I'm personally interested in but which may not have any immediate economic benefits.  A couple of years ago, after reading Penrose's "Road to Reality", I thought about applying Clifford algebra ideas to fracture mechanics and wrote up a proposal to that effect.  The proposal wasn't funded, but I think the idea is worth exploring.

The summary of the proposal was

Naturally negative bulk modulus material.

My book on metamaterials, "An introduction to metamaterials and waves in composites" has been published on June 16, 2011 by CRC Press (Taylor and Francis).

The book is meant for students, researchers, engineers, and educators who want to get a basic grounding on the theory that is the basis of recent excitement about negative materials, cloaking, transformation optics/acoustics and other wave phenomena in composites.

The word "failure" can mean different things to different people.  Over the past couple of years, my interactions with various groups from industry has shown me that for some people failure means catastropic fracture/buckling while for others it can mean highly localized plastic yielding.  Even for relatively simple sandwich composite structures, there is no clearly agreed upon definition of the word.

Yesterday, as I was waiting for the rain to stop before I could walk home from work, a stranger accosted me in the lobby of the building.  He asked me what I did, to which I replied "Mechanics".  He mulled over the answer for a bit and asked me to be more specific, at which point I said that we were trying to design materials that could guide waves around objects.  He said "Water waves?".  I replied "All types of waves."  Clearly, common words can mean quite different things to different people.

There are a couple of funded PhD positions available at the University of Auckland, New Zealand.

The topics are, roughly, 

1) Advanced material models and variability

2) Biomimetic sensing and adhesion.

The deadline for applications is Friday, October 29, 2010.  Please send a current CV, a statement of purpose, and transcripts/grades from your undergraduate work (and master's work if you have a master's degree in a related field).

PDF files of the advertisements for the positions (containing the e-mails of persons to contact) are attached.

-- Biswajit

I was hoping to see Abaqus or Ansys as the top words. Instead I see help, thanks, stress and incident.