Amit Acharya's blog

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Deformation 'Gradient', Right/Left Cauchy Green Compatibility

I post some (hand-written) notes on compatibility conditions for both small and finite strains that I have used for helping me in lecturing. These may be useful for our student friends on imechanica. I also post a paper on compatibility conditions for the Left Cauchy-Green field in three dimensions as well as the paper by Janet Blume on the same subject.


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Geometric Dislocation tensor in finite plasticity

The criteria of Cermelli and Gurtin (2001, J. Mech. Phys. Solids) for choosing a geometric dislocation tensor in finite plasticity are reconsidered. It is shown that physically reasonable alternate criteria could just as well be put forward to select other measures; overall, the emphasis should be on the connections between various physically meaningful measures as is customary in continuum mechanics and geometry, rather than on criteria to select one or another specific measure.


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Void expansion as wave phenomena - might damage evolution be mathematically related to fluid dynamics and turbulence?

The main idea is the following: a most natural mathematical setup for considering the motion of the void-solid interface of an expanding void is that of the traveling wave. Thus, a theory for macroscopic damage evolution may be suspected as being a homogenized version of basic theory that has such wave phenomena as an essential ingredient. This paper is a first step in probing such questions. 


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Science, as some see it...

I came across some content I used to have on my webpage a long time ago.

http://www.ce.cmu.edu/~amita/webpage_misc.html

Hopefully it is inspirational for that bright, young, graduate student waiting in the wings to usher in the revolution that shows us how to solve some of the outstanding theoretical problems of solid mechanics that we seem to put off  e.g. concrete, quantitative methods for calculating time-dependent microstructure in plasticity and its effect on time-dependent macroscopic properties.....

For those who read the link, do not miss Faraday's quote and Rota's "Ten lessons...'


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Musings on continuum thermodynamic formalism and (yet another) damage model

A technique for setting up generalized continuum theories based on a balance law and nonlocal thermodynamics is suggested. The methodology does not require the introduction of gradients of the internal variable in the free energy. Elements of a generalized damage model with porosity as the internal variable are developed as an example.


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New perspectives in plasticity theory

 

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.


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Does a radially expanding cylinder bend?

 The Koiter-Sanders-Budiansky bending strain measure and a nonlinear generalization

 We know from strength of materials that non-uniform stretching of fibers along the cross section of a beam produces bending moments. But does this situation necessarily correspond to a 'bending' deformation? For that matter, what do we exactly mean kinematically when we talk about a bending deformation?

To make the question more concrete, consider a cylinder that expands uniformly along all radial rays. Does this deformation of the cylinder correspond to bending? I think it is fair to say that most would say that this is purely a stretching deformation with no bending. But then, what is precisely a bending deformation?


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papers related to reply: apparent randomness continues

Two papers are attached related to randomness discussion.


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Toward averaging nonlinear dynamics

Attached is a paper outlining ideas for averaging autonomous dynamics, based on a dynamical systems point of view.

People interested in computational multiscale modeling, especially of the sequential kind, as well as nonequilibrium statistical mechanics may find these ideas useful.


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