iMechanica - Yield stress
https://imechanica.org/taxonomy/term/4117
enOnset of Plasticity via Relaxation Analysis (OPRA)
https://imechanica.org/node/19577
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/169">Plasticity</a></div><div class="field-item odd"><a href="/taxonomy/term/4117">Yield stress</a></div><div class="field-item even"><a href="/taxonomy/term/11018">elastic limit</a></div><div class="field-item odd"><a href="/taxonomy/term/1257">yield surface</a></div><div class="field-item even"><a href="/taxonomy/term/11019">mobile dislocation.</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><strong>ABSTRACT</strong></p>
<p>In crystalline metals and alloys, plasticity occurs due to the movement of mobile dislocations and the yield stress for engineering applications is traditionally quantified based on strain. The onset of irreversible plasticity or “yielding” is generally identified by a deviation from linearity in the stress-strain plot or by some standard convention such as 0.2% offset strain relative to the “linear elastic response”. In the present work, we introduce a new methodology for the determination of the true yield point based on stress relaxation. We show experimentally that this determination is self-consistent in nature and, as such, provides an objective observation of the very onset of plastic flow. Our designation for yielding is no longer related to the shape of the stress-strain curve but instead reflects the earliest signature of the activation of concerted irreversible dislocation motion in a test specimen under increasing load.</p>
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</div></div></div>Mon, 07 Mar 2016 02:00:47 +0000Amit Pandey19577 at https://imechanica.orghttps://imechanica.org/node/19577#commentshttps://imechanica.org/crss/node/19577Yield stress fluid flows
https://imechanica.org/node/17467
<div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/4117">Yield stress</a></div><div class="field-item odd"><a href="/taxonomy/term/4172">Fluid flow</a></div><div class="field-item even"><a href="/taxonomy/term/608">research</a></div><div class="field-item odd"><a href="/taxonomy/term/1636">experiments</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>A Virtual Special Issue of the <a href="http://www.journals.elsevier.com/journal-of-non-newtonian-fluid-mechanics/"><em>Journal of Non-Newtonian Fluid Mechanics </em></a>devoted to <strong>yield stress fluid flows</strong> has just been released. With this first Virtual Special Issue of the journal we inaugurate a practice, which we plan to make regular, of highlighting developments on a particular subject of relevance in order to guide and encourage research in the field. Each virtual special issue will be built around a recent invited review paper by a leading expert and consist of links to recent, and some not-so-recent, JNNFM papers in the field of the review. These papers, which we select with advice from the author of the review, will showcase a wide range of high-quality contributions to illustrate the wealth and vigor of the topic.</p>
<p>We are delighted that <strong><a href="http://www.sciencedirect.com/science/article/pii/S0377025714000895"><span><span>Philippe Coussot</span></span></a></strong> was willing to write the first review article in this new series, on the topic of experimental studies of yield stress fluids. We have chosen 15 papers to complement this review, beginning with the experimental work of <strong><a href="http://www.sciencedirect.com/science/article/pii/S0377025712002248"><span><span>Jossic et al</span></span></a>.</strong> (2013). This study of creeping flow around a perpendicular disc, is a good illustration of the interesting flow physics that remain to be investigated with complex fluids in classical flows. The next several papers address the technologically-important topic of two-phase flows of yield-stress fluids: the experiments of <a href="http://www.sciencedirect.com/science/article/pii/S0377025708002140"><span><span>Sikorski et al</span></span></a>. (2009) on bubbles rising on yield stress fluids, the interesting and original experiments on droplets of yield stress fluids by <a href="http://www.sciencedirect.com/science/article/pii/S0377025710001096"><strong><span><span>German and Bertola</span></span></strong></a> (2010) and finally a theoretical analysis of droplet formation, together with some experiments, by <a href="http://www.sciencedirect.com/science/article/pii/S0377025710001618"><span><span>Balmforth et al.</span></span></a> (2010). <a href="http://www.sciencedirect.com/science/article/pii/S0377025711002412"><strong><span><span>Taghavi et al</span></span></strong></a>. (2012) is next, experimentally characterizing fluid displacement of a buoyant miscible yield stress fluid by a denser Newtonian fluid, a very important problem in drilling.</p>
<p>While the opening review paper deals only with laminar flows, yield stress fluid flows are also important under transitional and turbulent flow conditions, as in the pipe flow experiments of <a href="http://www.sciencedirect.com/science/article/pii/S0377025705000704"><strong><span><span>Peixinho et al.</span></span></strong></a> (2005), another case of relevance to drilling. We close the showcase of experiments with the contribution of <a href="http://www.sciencedirect.com/science/article/pii/S0377025711001182"><strong><span><span>Rensing et al</span></span></strong></a>. (2011) on ice slurries in water-in-oil emulsions showing that yield stress fluids can be found with unusual combinations of components.</p>
<p>Numerical investigations of yield stress fluid flows are increasingly useful and popular. The numerical methods have to deal with the yield condition and there are two approaches to doing so: regularization facilitates the governing equations by introducing a high viscosity fluid at low shear rates, thus transforming the yield stress material into a fluid, but it is an approximation and the location of the yield surface becomes ill-defined. This is well shown by <a href="http://www.sciencedirect.com/science/article/pii/S0377025706002898"><span><span>Mitsoulis </span></span></a>(2007) in his work on extrudate swell, a very relevant problem for polymer processing. Lagrangian tracking methods explicitly compute the yield surface and do not approximate the material as a fluid, but are computationally more complex. This is illustrated by <a href="http://www.sciencedirect.com/science/article/pii/S0377025705000911"><strong><span><span>Huilgol and You</span></span></strong></a> (2005) in their application to pipe flow of various yield stress fluid models. The last paper in this section, by <a href="http://www.sciencedirect.com/science/article/pii/S0377025712002315"><span><span>Dimakopoulos et al</span></span></a>. (2013), compares both approaches in their numerical computations of steady bubble rise in a yield stress fluid.</p>
<p>To illustrate the diversity of applications where yield stress fluids are of relevance three works were selected. Two-phase flows with a solid phase are here represented by the computations of<a href="http://www.sciencedirect.com/science/article/pii/S0377025703001113"><span><span> Liu et al</span></span></a>. (2003) on the interactions between moving rigid spheres in a Bingham material. The restart of pipeline flows of waxy crude oils by <a href="http://www.sciencedirect.com/science/article/pii/S0377025706000711"><strong><span><span>Vinay et al</span></span></strong></a>. (2006) is relevant for flow assurance in the oil industry and the detailed investigation of <a href="http://www.sciencedirect.com/science/article/pii/S0377025710001357"><strong><span><span>Turan et al</span></span></strong></a>. (2010) on free convection of Bingham fluids in a 2D square enclosure with differentially heated walls presents useful heat transfer correlations.</p>
<p>Analytical approaches to a problem provide the most complete and elegant picture of its solution, if it exists. A good example is the analysis of the squeeze flow of a cylindrical sample of a yield stress paste between parallel plates by <a href="http://www.sciencedirect.com/science/article/pii/S0377025705000959"><span><span>Sherwood </span></span></a>(2002). Last, but not least, the modeling of yield stress fluids can be actually rather complex because the yield stress is often combined with such characteristics as thixotropy. The development of adequate rheological constitutive equations for such materials is well shown by <strong><a href="http://www.sciencedirect.com/science/article/pii/S0377025709001578"><span><span>Souza Mendes</span></span></a></strong> (2009).</p>
<p>We hope you enjoy reading or revisiting these contributions and that doing so will lead to new research ideas and insights. Several further invited reviews and their corresponding virtual special issues are in progress and we look forward to presenting these in the near future.</p>
<p><em>Editors of the Journal of Non-Newtonian Fluid Mechanics<br /></em>Fernando Pinho, University of Porto, Portugal<br />Mike Graham, University of Wisconsin-Madison, USA</p>
<p><em>Executive Publisher, Elsevier<br /></em>Keith Lambert</p>
</div></div></div>Fri, 07 Nov 2014 11:02:21 +0000Korporaald17467 at https://imechanica.orghttps://imechanica.org/node/17467#commentshttps://imechanica.org/crss/node/17467Stress-induced phase transformation and pseudo-elastic/pseudo-plastic recovery in intermetallic Ni–Al nanowires
https://imechanica.org/node/5964
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/93">molecular dynamics</a></div><div class="field-item odd"><a href="/taxonomy/term/558">shape memory</a></div><div class="field-item even"><a href="/taxonomy/term/1691">elastic modulus</a></div><div class="field-item odd"><a href="/taxonomy/term/1744">nanowire</a></div><div class="field-item even"><a href="/taxonomy/term/4114">Martenistic Phase Transformation</a></div><div class="field-item odd"><a href="/taxonomy/term/4115">Embedded Atom Method</a></div><div class="field-item even"><a href="/taxonomy/term/4116">Pseudo-elastic/pseudo-plastic</a></div><div class="field-item odd"><a href="/taxonomy/term/4117">Yield stress</a></div><div class="field-item even"><a href="/taxonomy/term/4118">B2</a></div><div class="field-item odd"><a href="/taxonomy/term/4119">BCT</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
Dear friends,
</p>
<p>
I want to share our recent research work on NiAl nanowire, which is published in Nanotechnology, IOP publishing. The abstract of the paper is given below. Further details can be found at "<span class="cite"><span class="cite_authors">Vijay Kumar Sutrakar <em>et al</em></span> 2009 <em class="cite_journal_full">Nanotechnology</em> <strong class="cite_volume">20</strong> 295705 (9pp) doi: <a href="http://dx.doi.org/10.1088/0957-4484/20/29/295705">10.1088/0957-4484/20/29/295705</a>"</span>
</p>
<p>
</p>
<p>
<strong class="abs_abstitle">Abstract.</strong><br />
Extensive molecular dynamics (MD) simulations have been performed in a B2-NiAl<br />
nanowire using an embedded atom method (EAM) potential. We show a stress induced<br /><img src="http://ej.iop.org/images/0957-4484/20/29/295705/nano307169ieqn1.gif" alt="\mathrm {B2} \to \mathrm {body} " align="middle" />-centered-tetragonal (BCT) phase transformation and a novel temperature and cross-section dependent<br />
pseudo-elastic/pseudo-plastic recovery from such an unstable BCT phase with a recoverable strain<br />
of ~30%<br />
as compared to 5–8% in polycrystalline materials. Such a temperature and cross-section<br />
dependent pseudo-elastic/pseudo-plastic strain recovery can be useful in various<br />
interesting applications of shape memory and strain sensing in nanoscale devices.<br />
Effects of size, temperature, and strain rate on the structural and mechanical<br />
properties have also been analyzed in detail. For a given size of the nanowire<br />
the yield stress of both the B2 and the BCT phases is found to decrease with<br />
increasing temperature, whereas for a given temperature and strain rate the yield<br />
stress of both the B2 and the BCT phase is found to increase with increase in<br />
the cross-sectional dimensions of the nanowire. A constant elastic modulus of<br />
~80 GPa of the B2 phase is observed in the temperature range of 200–500 K for nanowires of<br />
cross-sectional dimensions in the range of 17.22–28.712 Å, whereas the elastic modulus of<br />
the BCT phase shows a decreasing trend with an increase in the temperature.
</p>
</div></div></div>Sun, 05 Jul 2009 08:04:00 +0000Vijay Kumar Sutrakar5964 at https://imechanica.orghttps://imechanica.org/node/5964#commentshttps://imechanica.org/crss/node/5964