iMechanica  stress concentrations
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STRESS DISTRIBUTION IN NANOTUBES
https://imechanica.org/node/3997
<div class="field fieldnametaxonomyvocabulary6 fieldtypetaxonomytermreference fieldlabelhidden"><div class="fielditems"><div class="fielditem even"><a href="/taxonomy/term/128">education</a></div></div></div><div class="field fieldnametaxonomyvocabulary8 fieldtypetaxonomytermreference fieldlabelhidden"><div class="fielditems"><div class="fielditem even"><a href="/taxonomy/term/264">carbon nanotubes</a></div><div class="fielditem odd"><a href="/taxonomy/term/468">mechanical properties</a></div><div class="fielditem even"><a href="/taxonomy/term/683">stress concentrations</a></div><div class="fielditem odd"><a href="/taxonomy/term/2894">aspect ratio</a></div></div></div><div class="field fieldnamebody fieldtypetextwithsummary fieldlabelhidden"><div class="fielditems"><div class="fielditem even"><p align="justify"><span><em><span>(All my simulations and research is conducted under guidance of respected <strong>Dr. Henry Tan</strong>, <strong>Uni. of Manchester</strong>)</span></em></span></p>
<p align="justify"><span><strong>STRESS DISTRIBUTION IN NANOTUBES</strong></span></p>
<p align="justify"><span><span>Nanotubes <span>are long tiny cylinders of graphite structure with caps at each end. <span>Carbon nanotubes have large interfacial area per volume and hold extraordinary mechanical, electrical as well as thermal properties.</span>The length to diameter ratio also called as aspect ratio plays an vital role in</span><span> describing the efficiency of nanotubes as reinforced material. For better mechanical load transfer the surface area of the fibre should be more which is provided by carbon nanotubes. </span></span> </span></p>
<p align="justify"><span><span><span><span><span>When an unidirectional nanotubes reinforced polymer is subjected to a tensile load in the nanotubes i.e. in fibres direction, then </span><span>stress transfers from the polymer matrix to the nanotubes by shear stress at the interface of nanotubes and polymeric matrix .</span><span>The source of the interfacial shear stress is the difference between deformations of nanotubes and the polymer matrix </span><span>surrounding it. The interfacial shear stress acts in the longitudinal direction of the nanotubes around its periphery.</span></span></span></span></span></p>
<p><span><span><span><span><span><span>In case of normal stress distribution in nanotubes fibres are considered, <strong><em>the axial stress increases gradually from its ends </em></strong></span></span><span><span><strong><em>and reaches to a maximum value at the central part</em></strong> represents special feature of long nanotube fibre. </span><span>The reason behind </span></span><span><span>this is, as u</span><span>nlike conventional fibre reinforced polymer composites, large interfacial areas are available for the load transfer in </span></span><span><span>carbon nanotubes reinforced composites due to the high aspect ratio of carbon nanotubes.</span><span> </span></span> </span></span></span></span></p>
<p class="MsoNormal" align="justify"><span><span><span>In addition to this, <strong><em>maximum shear stress is maximum/highest near the fibre ends but it reduces rapidly to near zero value or almo</em></strong></span></span><span><span><strong><em>st </em></strong></span></span><span><span><strong><em>negligible value towards the midlength of the nanotubes</em></strong>. This nature of shear stress distribution is totally opposite to normal stress </span></span><span><span>distribution in long nanotubes fibres. <span>The concentration of shear stress is limited to a very small nanosize region, which seems to </span></span></span><span><span><span>be a beneficial characteristic of nanotubes.</span></span></span> </span></p>
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Tue, 07 Oct 2008 08:09:19 +0000
Yogesh Bansod
3997 at https://imechanica.org
https://imechanica.org/node/3997#comments
https://imechanica.org/crss/node/3997

Biologically inspired design—natural convex joints reduce stress concentrations
https://imechanica.org/node/978
<div class="field fieldnamebody fieldtypetextwithsummary fieldlabelhidden"><div class="fielditems"><div class="fielditem even"><p>Finite element stress analysis and corner optimization of a treesteel railing interface/joint <strong>(Mattheck, 1998)</strong> showed that the naturally formed tree/railing joint was very effective in reducing stress concentration. Using this principle, we designed and tested convex interfacial joints of dissimilar engineering materials, and find that these new joints will significantly increase ultimate failure load and even reduce material volumes.<span> </span>Click here to read two related papers (<a href="http://people.vanderbilt.edu/~l.roy.xu/papers/EMpartI2004LRXHKSS.pdf">a. Xu, et al., Experimental Mechanics, 2004;</a> b. <a href="http://people.vanderbilt.edu/~l.roy.xu/papers/WangXu06MOM.pdf">Wang and Xu, Mechanics of Materials, 2006</a>).</p>
<p>Our Insitu photoelasticity experiments on polycarbonatealuminum joints showed that the freeedge stress singularity (leading to stress/fringe concentration) existed in the straightedge joint (first movie).© Dr. L. R. Xu (Vanderbilt University)</p>
<object width="425" height="350"><embed src="http://www.youtube.com/v/ssgfonEmlX4" type="application/xshockwaveflash" width="425" height="350"></embed></object><p>
However, for our proposed convex joint, freeedge stress singularity was successfully removed so no fringe concentration was observed at the specimen edges (second movie). © Dr. L. R. Xu (Vanderbilt University)</p>
<object width="425" height="350"><embed src="http://www.youtube.com/v/ebfbwa4MRqs" type="application/xshockwaveflash" width="425" height="350"></embed></object></div></div></div><div class="field fieldnametaxonomyextra fieldtypetaxonomytermreference fieldlabelabove"><div class="fieldlabel">Taxonomy upgrade extras: </div><div class="fielditems"><div class="fielditem even"><a href="/taxonomy/term/76">research</a></div><div class="fielditem odd"><a href="/taxonomy/term/682">Biologically inspired design</a></div><div class="fielditem even"><a href="/taxonomy/term/683">stress concentrations</a></div><div class="fielditem odd"><a href="/taxonomy/term/684">interface mechanics</a></div></div></div>
Mon, 05 Mar 2007 03:00:58 +0000
L. Roy Xu
978 at https://imechanica.org
https://imechanica.org/node/978#comments
https://imechanica.org/crss/node/978