iMechanica - Comments for "On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces"
https://www.imechanica.org/node/20731
Comments for "On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces"enPastewka and Robbins criterion is found clearly wrong at last
https://www.imechanica.org/comment/30568#comment-30568
<a id="comment-30568"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>We recently found that Pastewka and Robbins criterion, on which we were always suspicious about the "fractal limit", is indeed wrong, as the numerical observations are limited to very narrow surface roughness spectra, and PR criterion is in contrast with results of BAM of Ciavarella, Persson-Scaraggi, and Persson Tosatti.</p>
<p>See here:</p>
<p> </p>
<p><span class="title-text">Universal features in “stickiness” criteria for soft adhesion with rough surfaces</span><span class="sr-only">Author links open overlay panel</span><a class="author size-m workspace-trigger" href="https://www.sciencedirect.com/science/article/pii/S0301679X1930547X?casa_token=gFuKp7vmrnkAAAAA:qLitS_0E0egAMYrhymKm7gCq0Wwtlv-2ZNZMdugbzqrlPUrLYqP8tU99EYRc3HTgRyoJxBLw#!" name="bau000001" id="bau000001"><span class="content"><span class="text given-name">M.</span><span class="text surname">Ciavarella</span></span></a><span class="button-text">Show more</span><span class="button-link-text">Add to Mendeley</span><span class="button-text">Share</span><span class="button-text">Cite</span><a class="doi" title="Persistent link using digital object identifier" href="https://doi.org/10.1016/j.triboint.2019.106031" target="_blank" rel="noopener noreferrer">https://doi.org/10.1016/j.triboint.2019.106031</a><a class="rights-and-content" href="https://s100.copyright.com/AppDispatchServlet?publisherName=ELS&contentID=S0301679X1930547X&orderBeanReset=true" target="_blank" rel="noopener noreferrer">Get rights and content</a> Highlights<br /></p><p id="d1e560"> </p>
<dl class="list"><dt class="list-label">•</dt>
<dd class="list-description">
<p id="d1e566">We derive a stickiness criterion from the simple Persson and Tosatti theory of adhesion of rough solids.</p>
</dd>
<dt class="list-label">•</dt>
<dd class="list-description">
<p id="d1e571">We derive another stickiness criterion from the BAM (Bearing Area Model) theory of Ciavarella.</p>
</dd>
<dt class="list-label">•</dt>
<dd class="list-description">
<p id="d1e576">We compare the two derived new criteria with that Violano et al., and Pastewka and Robbins and Muser.</p>
</dd>
<dt class="list-label">•</dt>
<dd class="list-description">
<p id="d1e581">We find Persson–Tosatti, BAM, and Violano criteria give very close results, and are mainly dependent on macroscopic quantities, while Pastewka and Robbins and Muser criteria differ from the previous three in that they depend on the truncation of the spectrum of roughness.</p>
</dd>
</dl><p> </p>
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</ul>Mon, 22 Feb 2021 06:01:33 +0000Mike Ciavarellacomment 30568 at https://www.imechanica.orgthis paper gives yet another simple interpretation
https://www.imechanica.org/comment/29070#comment-29070
<a id="comment-29070"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p> </p>
<p>This recent paper shows a yet more radical view on PR results, where the conclusion is just the opposite: slopes and curvatures have no role at all on stickiness!</p>
<p><a href="http://imechanica.org/node/21262">A very simple estimate of adhesion of hard solids with rough surfaces based on a bearing area model</a></p>
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</ul>Sun, 28 May 2017 12:25:30 +0000Mike Ciavarellacomment 29070 at https://www.imechanica.orgThe paper is now available online
https://www.imechanica.org/comment/29039#comment-29039
<a id="comment-29039"></a>
<p><em>In reply to <a href="https://www.imechanica.org/comment/28782#comment-28782">Pure coincidence DMT approx work in Pastewka-Robbins model?</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>On the use of DMT approximations in adhesive contacts, with remarks on random rough contacts<br /></p><ul class="authorGroup noCollab svAuthor"><li class="smh5"><a id="authname_N64f3d768N53e03310" class="authorName svAuthor" href="http://www.sciencedirect.com/science/article/pii/S0301679X17302190#" data-orcid="" data-t="a" data-fn="M." data-ln="Ciavarella" data-pos="1" data-tb="">M. Ciavarella</a> </li>
</ul><p> <a class="showLess moreLink" tabindex="0"><span class="CollapseText"> </span><span class="showInfo expand" title="Show more author and article information">Show more</span></a><br /></p><dl class="extLinks nonEmpty"><dd class="doiLink"></dd>
<dd class="doi"><a id="ddDoi" class="S_C_ddDoi" href="http://doi.org/10.1016/j.triboint.2017.04.046" target="doilink">http://doi.org/10.1016/j.triboint.2017.04.046</a></dd>
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</dl><p> Highlights<br /></p><p id="sp0035"> </p>
<dl id="list_li0005" class="listitem"><dt class="label">•</dt>
<dd>
<p id="p0005">The approximation of the DMT theory (to neglect deformations due to attractive forces), is receiving some new interest.</p>
</dd>
<dt class="label">•</dt>
<dd>
<p id="p0010">We show it leads to extremely large overestimations of the adhesive forces in the case of spherical contact, even at relatively small Tabor parameters, except at pull-off.</p>
</dd>
<dt class="label">•</dt>
<dd>
<p id="p0015">For cylindrical contact, the opposite trend is found: DMT now overestimates pull-off by large factors, but for larger contact areas, the error becomes in the opposite direction.</p>
</dd>
<dt class="label">•</dt>
<dd>
<p id="p0020">This may explain why some partial success has been found for rough contacts in some limited range of parameters, considering the geometry of contacts can be very elongated.</p>
</dd>
</dl><p> </p>
<p>Abstract<br /></p><p id="sp0030">The contact between rough surfaces with adhesion is an extremely difficult problem, and the approximation of the DMT theory (to neglect deformations due to attractive forces), originally developed for spherical contact of very small radius, is receiving some new interest. The DMT approximation leads to extremely large overestimations of the adhesive forces in the case of spherical contact, except at pull-off. For cylindrical contact, the opposite trend is found for larger contact areas. These findings suggest some caution in solving rough contacts with DMT models, unless the Tabor parameter is really low. Further approximate models like that of Pastewka & Robbins’ may be explained to work only due to a coincidence of error cancellation in their range of parameters.</p>
<p>Keywords<br /></p><ul id="key0005" class="keyword"><li id="key0010" class="svKeywords"><span id="">Adhesion</span>; </li>
<li id="key0015" class="svKeywords"><span id="">Maugis' theory</span>; </li>
<li id="key0020" class="svKeywords"><span id="">Rough surfaces</span>; </li>
<li id="key0025" class="svKeywords"><span id="">DMT theory</span>; </li>
<li id="key0030" class="svKeywords">JKR theory</li>
</ul><p><span><span> </span></span></p>
<p><span><span>Article title: On the use of DMT approximations in adhesive contacts, with remarks on random rough contacts</span></span></p>
<p><span><span>Article reference: JTRI4712</span></span></p>
<p><span><span>Journal title: Tribology International</span></span></p>
<p><span><span>Corresponding author: Prof Michele Ciavarella</span></span></p>
<p><span><span><a href="http://dx.doi.org/10.1016/j.triboint.2017.04.046">http://dx.doi.org/10.1016/j.triboint.2017.04.046</a></span></span></p>
<p> </p>
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</ul>Thu, 27 Apr 2017 16:09:58 +0000Mike Ciavarellacomment 29039 at https://www.imechanica.organ interesting new paper shows Guduru effect and then reduction
https://www.imechanica.org/comment/29029#comment-29029
<a id="comment-29029"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>This interesting <a href="http://www.sciencedirect.com/science/article/pii/S0301679X17301640">new paper</a> shows for the first time some simulations of the Guduru increase of adhesion pull-off due to roughness, decaying then after reaching a maximum, also for random roughness (although the effect is small).</p>
<p>Needless to say, there is no reference to the strange result of Pastewka-Robbins, but rather pull-off is always shown to depend on rms roughness as most commonly expected.</p>
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</ul>Mon, 17 Apr 2017 19:20:30 +0000Mike Ciavarellacomment 29029 at https://www.imechanica.orgSurface generator: artificial randomly rough surfaces in MATLAB
https://www.imechanica.org/comment/29005#comment-29005
<a id="comment-29005"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>Surface generator: artificial randomly rough surfaces
</p><p><a href="https://it.mathworks.com/matlabcentral/fileexchange/60817-surface-generator--artificial-randomly-rough-surfaces">https://it.mathworks.com/matlabcentral/fileexchange/60817-surface-genera...</a></p>
<p>In general this may be useful, with related routines</p>
<p><a href="https://it.mathworks.com/matlabcentral/profile/authors/4185331-mona-mahboob-kanafi">https://it.mathworks.com/matlabcentral/profile/authors/4185331-mona-mahb...</a></p>
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</ul>Wed, 05 Apr 2017 19:37:51 +0000Mike Ciavarellacomment 29005 at https://www.imechanica.orginteresting JKR method for rough surface from Caltech & Berlin
https://www.imechanica.org/comment/28996#comment-28996
<a id="comment-28996"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p><span>I found Caltech people suggested recently an interesting way to model JKR adhesion, which had been suggested already by Popov people in Berlin --- in fact I told the Caltech people in fact that Popov found it before and they cited in the end.</span></p>
<p> Any interest to experiment it? It is based on springs that have a highest traction, which depends on mesh size with a power law that turn out reproducing JKR singularity <a href="https://arxiv.org/pdf/1606.03166.pdf" target="_blank" data-saferedirecturl="https://www.google.com/url?hl=en-GB&q=https://arxiv.org/pdf/1606.03166.pdf&source=gmail&ust=1491125961231000&usg=AFQjCNH8I99zP86Qx6bTLWh1rFKQgedSKg">https://arxiv.org/pdf/1606.03166.pdf</a> <a href="http://casopisi.junis.ni.ac.rs/index.php/FUMechEng/article/view/764" data-clk="hl=it&sa=T&ct=res&cd=0&ei=nmjfWK2nDIzvmAGVjZPgCA">Adhesive contact simulation of elastic solids using local mesh-dependent detachment criterion in boundary elements method</a><a href="https://scholar.google.it/citations?user=S7dDm_cAAAAJ&hl=it&oi=sra">R Pohrt</a>, <a href="https://scholar.google.it/citations?user=oQ4sHxgAAAAJ&hl=it&oi=sra">VL Popov</a> - Facta Universitatis, Series: Mechanical …, 2015 - casopisi.junis.ni.ac.rsAbstract Using the concept of stress intensity factors, we suggest a way to include adhesion <br />into boundary elements simulation of contacts. A local criterion concerning the maximum <br />admissible surface stresses decides whether the adhesive bonds in particular grid points fail <br />or not. By taking into account the grid spacing, a robust methodology is found. Validation is <br />done using the theoretically derived cases of JKR adhesion.<a href="https://scholar.google.it/scholar?cites=1908459610558899105&as_sdt=2005&sciodt=0,5&hl=it">Citato da 3</a> <a href="https://scholar.google.it/scholar?q=related:oSOLg-c1fBoJ:scholar.google.com/&hl=it&as_sdt=0,5&as_ylo=2013">Articoli correlati</a> <a class="gs_nph" href="https://scholar.google.it/scholar?cluster=1908459610558899105&hl=it&as_sdt=0,5&as_ylo=2013">Tutte e 5 le versioni</a> <a class="gs_nph" href="https://scholar.google.it/scholar?q=Adhesive+contact+simulation+of+elastic+solids+using+local+mesh-+dependent+detachment+criterion+in+boundary+elements+method&btnG=&hl=it&as_sdt=0%2C5&as_ylo=2013#">Cita</a> <span class="gs_nph"><a id="gs_svl0" title="Salva questo articolo nella mia biblioteca per leggerlo o citarlo più tardi." href="https://scholar.google.it/scholar?q=Adhesive+contact+simulation+of+elastic+solids+using+local+mesh-+dependent+detachment+criterion+in+boundary+elements+method&btnG=&hl=it&as_sdt=0%2C5&as_ylo=2013#">Salva</a></span></p>
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</ul>Sat, 01 Apr 2017 09:42:08 +0000Mike Ciavarellacomment 28996 at https://www.imechanica.orgBesides, even Persson's study are against Pastewka & Robbins
https://www.imechanica.org/comment/28989#comment-28989
<a id="comment-28989"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>Mulakaluri, N., Persson, B.: Adhesion between elastic solids with randomly rough surfaces: comparison of analytical theory with molecular-dynamics simulations. Europhys. Lett. 96, 66003 (2011) <a href="https://arxiv.org/pdf/1112.5275" data-clk="hl=en&sa=T&oi=gga&ct=gga&cd=0&ei=p3zZWJeYBMShjAHBr77IBQ"><span class="gs_ctg2">[PDF]</span> arxiv.org</a> </p>
<p>In all the figures, from fig.2 to fig.5, the MAIN parameter ruling pull-off is RMS roughness.... against PR criterion. The puzzle continues...</p>
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</ul>Mon, 27 Mar 2017 20:57:36 +0000Mike Ciavarellacomment 28989 at https://www.imechanica.orgI wonder how Pastewka & Robbins would justify Fig11 experiments
https://www.imechanica.org/comment/28984#comment-28984
<a id="comment-28984"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p> PR argue that their findings suggests stickiness in strong contrast to the classical findings of FT, whose emphasis in on rms amplitude of roughness, whereas their findings are independent on it.</p>
<p>I wonder how this can be reconciled with the pull-off experiments in Fig.11 from the literature on our recent paper</p>
<p><a href="http://www.tandfonline.com/eprint/aNhs6YfWn7P23MPZa6Dh/full" target="_blank" data-saferedirecturl="https://www.google.com/url?hl=en-GB&q=http://www.tandfonline.com/eprint/aNhs6YfWn7P23MPZa6Dh/full&source=gmail&ust=1490621349899000&usg=AFQjCNFcZuXHrHIwLMLHDqD7v74v02N30w">http://www.tandfonline.com/eprint/aNhs6YfWn7P23MPZa6Dh/full</a><span> </span></p>
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</ul>Sun, 26 Mar 2017 13:36:28 +0000Mike Ciavarellacomment 28984 at https://www.imechanica.orgthe problem is still unsolved!
https://www.imechanica.org/comment/28971#comment-28971
<a id="comment-28971"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>While the asperity model shows qualitatively similar results to Pastewka and Robbins for the pull-off value (and therefore main dependence on m0, as suggested also by the recent very elegant Persson's extended solution by Junki Joe Scaraggi and Barber), the <span>area-load </span><span>slope (not necessarily a very interesting quantity) predicted by PR is in contrast to asperity models. Anyone joining the effort to solve the puzzle?</span></p>
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</ul>Sat, 18 Mar 2017 21:56:59 +0000Mike Ciavarellacomment 28971 at https://www.imechanica.orgAn asperity model for adhesion between rough surfaces
https://www.imechanica.org/comment/28968#comment-28968
<a id="comment-28968"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p><strong data-reactid="44">Article</strong><span data-reactid="45"> <span class="publication-meta-separator" data-reactid="47">in</span> <span class="publication-meta-journal" data-reactid="49">Journal of Adhesion Science and Technology</span></span><span data-reactid="50"> · March 2017</span> <span data-reactid="54">DOI: 10.1080/01694243.2017.1304856</span><br /></p><ul data-reactid="56"><li class="publication-author-list-item" data-reactid="57"><span class="publication-author-position" data-reactid="62">1st</span> <span class="publication-author-name" data-reactid="64">Michele Ciavarella</span></li>
<li class="publication-author-list-item" data-reactid="57"><span class="publication-author-position" data-reactid="72">2nd</span> <a class="publication-author-name ga-author-name" href="https://www.researchgate.net/profile/Antonio_Papangelo" data-reactid="74">Antonio Papangelo</a> · Technische Universität Hamburg</li>
</ul><p> <span>A simple asperity model using random process theory is developed in the presence of adhesion, using the Derjaguin, Muller and Toporov model for each individual asperity. <strong>A new adhesion parameter is found, which perhaps improves the previous parameter proposed by Fuller and Tabor which assumed identical asperities</strong> – the model in all his variants for the radius always gives a finite pull-off force, as in Fuller and Tabor, and contrary to the exponential asperity height distribution, where the force is either always compressive, or always tensile. It is shown that a model with spheres having a radius only dependent on height is a reasonable approximation with respect to models having also a distribution of radius curvatures – the three models differ considerably, as opposed to the adhesionless case where these details did not matter. <strong>The important surface parameters in the theory determining the pull-off force are the three moments m0, m2, m4</strong>. The asymptotic form of the model at large separation is solved in closed form. As the theoretical pull-off of aligned asperities having the same radius (the average value) increases with the square root of the Nayak bandwidth of the roughness, and as asperity models are known to describe less well the surface at large bandwidth parameters, the limit behavior at large bandwidths remains uncertain.</span><span><br /></span><span>Link to the paper: </span><a href="http://www.tandfonline.com/eprint/2tGWbVTiTXB4KJRVQEzi/full">http://www.tandfonline.com/eprint/2tGWbVTiTXB4KJRVQEzi/full</a> </p>
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</ul>Sat, 18 Mar 2017 19:21:37 +0000Antonio Papangelocomment 28968 at https://www.imechanica.orgAnother study which seems in contrast to Pastewka and Robbins
https://www.imechanica.org/comment/28927#comment-28927
<a id="comment-28927"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>I see this just accepted paper on <a href="http://www.sciencedirect.com/science/article/pii/S0301679X17301081">http://www.sciencedirect.com/science/article/pii/S0301679X17301081</a></p>
<p><a class="cLink" title="Go to Tribology International on ScienceDirect" href="http://www.sciencedirect.com/science/journal/0301679X">Tribology International</a><br /></p><p class="volIssue">Available online 3 March 2017</p>
<p class="articlePress"><span><a class="cLink" href="http://www.sciencedirect.com/science/journal/aip/0301679X">In Press, Accepted Manuscript</a></span> — <a class="FCANote" href="http://www.sciencedirect.com/science/article/pii/S0301679X17301081#FCANote">Note to users</a></p>
<p><a class="cLink" href="http://www.sciencedirect.com/science/journal/aip/0301679X"><img class="toprightlogo" src="http://ars.els-cdn.com/content/image/S0301679X.gif" alt="Cover image" /></a>
</p><p> </p>
<p> Effect of fine-scale roughness on the tractions between contacting bodies<br /></p><ul class="authorGroup noCollab svAuthor"><li class="smh5"><a id="authname_N4b2a6f60N6b6921b8" class="authorName svAuthor" href="http://www.sciencedirect.com/science/article/pii/S0301679X17301081#" data-orcid="" data-t="a" data-fn="Junki" data-ln="Joe" data-pos="1" data-tb="">Junki Joe</a><a id="baff0005" class="intra_ref auth_aff" title=" a" href="http://www.sciencedirect.com/science/article/pii/S0301679X17301081#aff0005">a</a>, <a id="bcor1" class="intra_ref auth_corr" title="Corresponding author contact information" href="http://www.sciencedirect.com/science/article/pii/S0301679X17301081#cor1"></a>, , </li>
<li class="smh5"><a id="authname_N4b2a6f60N6b692320" class="authorName svAuthor" href="http://www.sciencedirect.com/science/article/pii/S0301679X17301081#" data-orcid="" data-t="a" data-fn="M." data-ln="Scaraggi" data-pos="2" data-tb="">M. Scaraggi</a><a id="baff0010" class="intra_ref auth_aff" title=" b" href="http://www.sciencedirect.com/science/article/pii/S0301679X17301081#aff0010">b</a>, </li>
<li class="smh5"><a id="authname_N4b2a6f60N6b6923d4" class="authorName svAuthor" href="http://www.sciencedirect.com/science/article/pii/S0301679X17301081#" data-orcid="" data-t="a" data-fn="J.R." data-ln="Barber" data-pos="3" data-tb="">J.R. Barber</a><a id="baff0005" class="intra_ref auth_aff" title=" a" href="http://www.sciencedirect.com/science/article/pii/S0301679X17301081#aff0005">a</a></li>
</ul><p> </p>
<p>Persson’s theory for the elastic contact of rough surfaces is modified to include the compliance associated with an interface force law such as the Lennard-Jones law. We determine the effect of adding a small packet of waves on the probability distribution function [PDF] of the local interfacial gap (including the effect of elastic deformation). This procedure is then used iteratively to develop an algorithm for determining the PDF for a rough surface with a prescribed power spectral density. The results show that for untruncated quasi-fractal surfaces, the PDF then converges at large wavenumber, in contrast to the result when only elastic deformation is taken into account. If the roughness is restricted to wavenumbers greater than a certain critical value, the algorithm predicts a converged relation between nominal traction and mean gap that can be regarded as a modified interfacial force law describing the influence of just the fine-scale roughness on the contact. In particular, the area under the resulting curve can be interpreted as a measure of interface energy as reduced by this roughness. The remaining macroscopic features of the surface can then be described using the JKR methodology in combination with this modified interface energy.</p>
<p> </p>
<p> </p>
<p>This also seems in contrast to PR --- since the procedure converges when fine details are added, and hence the stickiness and any other property of the solution CANNOT depend on slopes and curvatures! Rather, this study also shows the main dependence on the rms amplitude.</p>
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</ul>Tue, 07 Mar 2017 08:13:56 +0000Mike Ciavarellacomment 28927 at https://www.imechanica.orgsorry, there was a mistake here
https://www.imechanica.org/comment/28919#comment-28919
<a id="comment-28919"></a>
<p><em>In reply to <a href="https://www.imechanica.org/comment/28913#comment-28913">What is the pull-off for theoretically flat surfaces?</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>Obviously despite there is an instability, the surfaces will jump into contact uniformly much before this instability appears. Sorry.</p>
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</ul>Thu, 02 Mar 2017 08:32:41 +0000Mike Ciavarellacomment 28919 at https://www.imechanica.orgWhat is the pull-off for theoretically flat surfaces?
https://www.imechanica.org/comment/28913#comment-28913
<a id="comment-28913"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>An interesting problem is the following: what happens for a truly flat surface? Even with a truncated potential, it is easy to show that the decaying adhesive force induces an instability --- even if the surface were flat. I have done the calculation for this instability, and it turns out, for the Lennard-Jones potential, that this instability occurs if we have a periodic wavelenght of the order of 50 a0. Therefore, not very large at all. Two flat surfaces would be in equilibrium at distance a0 and show the theoretical Lennard Jones pull-off force (theoretical strength) only if they were constrained not to assume wavy configurations.</p>
<p>This in fact could be an interesting problem to study, which however requires a numerical solution. Anyone interested?</p>
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</ul>Sat, 25 Feb 2017 11:12:52 +0000Mike Ciavarellacomment 28913 at https://www.imechanica.orgSome arguments on why Pastewka-Robbins is not general
https://www.imechanica.org/comment/28912#comment-28912
<a id="comment-28912"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>First of all, PR use a "truncated potentials", a convenient numerical representation of the Lennard-Jones potential, but certainly a numeric artefact. Their potential is truncated at a short distance, a0+delta_r where delta_r is of the order of a0 itself (the atomic distance), and therefore, there is an artificial effect there: after 2 atomic steps, there is no longer adhesive force. This perhaps hides some effects of the rms amplitude?</p>
<p>In a true situation, Lennard-Jones extends to infinity, and it is clear that this fact already lowers the significance of their finding. Even at very long distances, in theory one should always have some attractive force, and this cannot be zero, and this means the area-load bends in the tensile quadrant <em><strong>always</strong></em>. Their criterion therefore has a lot to do with their arbitrary definition of the truncated potential.</p>
<p> </p>
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</ul>Sat, 25 Feb 2017 11:10:41 +0000Mike Ciavarellacomment 28912 at https://www.imechanica.orgEffect of rms amplitude on adhesive behavior of surfaces
https://www.imechanica.org/comment/28910#comment-28910
<a id="comment-28910"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p><span>There is no qualitative contrast between classical asperity models and Persson models </span><span>or any numerical recent calculation about the slope of area-load curve: the only </span><span>geometrical parameter entering the area-load slope is the rms slope of the surface.</span> </p>
<p><span>The question arises with adhesion. Pastewka-Robbins suggested that the slope in this case </span><span>becomes dependent additionally on rms curvature, and not on rms amplitude, whereas </span><span>asperity models (Fuller-Tabor is the only one, the proper rough random surface one is </span><span>not in the Literature but we are about to publish it) involve also rms amplitude.</span> </p>
<p><span>However, also Pastewka-Robbins do find that pull-off depends on rms amplitude. </span><span>So in their case there is a curious threshold: for non-sticky surfaces, they say there </span><span>is no dependence on rms amplitude, whereas for sticky one there is, as they also find.</span></p>
<p> </p>
<p><span>Can you beleive this?</span></p>
<p> </p>
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</ul>Thu, 23 Feb 2017 12:11:14 +0000Antonio Papangelocomment 28910 at https://www.imechanica.orgAmodified form of Pastewka-Robbins criterion for adhesion
https://www.imechanica.org/comment/28902#comment-28902
<a id="comment-28902"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="http://www.tandfonline.com/doi/abs/10.1080/00218464.2017.1292139" data-clk="hl=en&sa=T&ct=res&cd=0&ei=vwmqWNvsOIOS2Ab6g5ywCA">Amodified form of <strong>Pastewka</strong>-Robbins criterion for adhesion</a><a href="https://scholar.google.it/citations?user=FcC7-AUAAAAJ&hl=en&oi=sra">M <strong>Ciavarella</strong></a>, <a href="https://scholar.google.it/citations?user=kUaZTJYAAAAJ&hl=en&oi=sra">A <strong>Papangelo</strong></a> - The Journal of Adhesion, 2017 - Taylor & Francis Abstract
</p><p>Recent numerical investigation on self-affine Gaussian surfaces by Pastewka & Robbins have led to a criterion for “stickiness” based on when the slope of the (repulsive) area-load relationship appears to become vertical in numerical simulations at a ratio of contact area to nominal one (rather arbitrarily) fixed to 1%. Since pull-off and slope of the area-load are two faces of the same medal, a simple check of the results in terms of pull-off shows that Pastewka & Robbins have many more data which fail their criterion than the ones who satisfy it, and this is evident even in their own Figures. As a small improvement, a proposal to modify the criterion to better fit their own data is put forward. However, the pull-off decay seems rather exponential so that it is unclear if their slope criterion really corresponds to a “thermodynamic” limit, and consequently their conclusion that stickiness should depend only on slopes and curvature may be an artefact of their assumption of defining a secant at 1% contact area ratio, rather than a true important property of rough contact. Both the PR criterion and the present modified one imply that for fractal dimension D<2.4<span>, stickiness should increase with resolution, so the problem of truncation of the spectrum seems ill-defined: in fact, PR define rigid self-affine surfaces with rather smooth and well defined slopes, and not a realistic atomic roughness as first studied by Luan and Robbins.</span></p>
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</ul>Sun, 19 Feb 2017 21:12:16 +0000Mike Ciavarellacomment 28902 at https://www.imechanica.orga mathematica code for surface generation
https://www.imechanica.org/comment/28901#comment-28901
<a id="comment-28901"></a>
<p><em>In reply to <a href="https://www.imechanica.org/comment/28897#comment-28897">The contact mechanics challenge: Problem definition</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>anyway, there is already one code in public domain mathematica <a href="http://demonstrations.wolfram.com/TwoDimensionalFractionalBrownianMotion/" target="_blank" data-saferedirecturl="https://www.google.com/url?hl=en-GB&q=http://demonstrations.wolfram.com/TwoDimensionalFractionalBrownianMotion/&source=gmail&ust=1487578668383000&usg=AFQjCNHn2QHRkBhpqG0iUEzrZ1nSWNqTxw">http://demonstrations.wolfram.com/TwoDimensionalFractionalBrownianMotion/</a></p>
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</ul>Sun, 19 Feb 2017 08:18:31 +0000Mike Ciavarellacomment 28901 at https://www.imechanica.orgThe contact mechanics challenge: Problem definition
https://www.imechanica.org/comment/28897#comment-28897
<a id="comment-28897"></a>
<p><em>In reply to <a href="https://www.imechanica.org/comment/28896#comment-28896">Very helpful material.</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>on numerical methods for rough contacts, almost everything has been said, you may look at<a href="https://arxiv.org/abs/1512.02403" data-clk="hl=en&sa=T&ct=res&cd=0&ei=5hynWILNM4mVmAGK2JPAAg">The <strong>contact </strong>mechanics <strong>challenge</strong>: Problem definition</a>
</p><p>That effort is going to appear as a paper soon in Trib. Letters. We discussed this in a recent Lorentz worshop. It has taken almost a decade after Persson's paper, to converge on some conclusions. Mainly because Persson never clearly said if his solution were exact or not: a very good trick to attract attention and citations! His solution in the end did result to be approximate, and not much better than asperity one.</p>
<p>His solution for load-separation is even worse, and in fact there is a little work to be done there, which perhaps I will do.</p>
<p>There is a lot more open problems in adhesion of course, as this entire discussion shows.</p>
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</ul>Fri, 17 Feb 2017 15:59:23 +0000Mike Ciavarellacomment 28897 at https://www.imechanica.orgVery helpful material.
https://www.imechanica.org/comment/28896#comment-28896
<a id="comment-28896"></a>
<p><em>In reply to <a href="https://www.imechanica.org/comment/28895#comment-28895">FEM is not very efficient, unless you want to deal with plastic</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>Wow! I searched a lot about this type of material/codes/notes that could help me kick start but I couldn't find much. These are hugely helpful for me. Are there any other forums/repositories/discussion boards where computational contact is discussed?</p>
<p> As I am fairly new to not just rough surface contact but to contact itself and already a bit familiar with FE we thought we'll start with something small just to get a feel of rough surface generation and contact. We (i.e me and my guide) haven't yet finalized on the directon. Thank you so much. </p>
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</ul>Fri, 17 Feb 2017 14:56:18 +0000Gouravarajucomment 28896 at https://www.imechanica.orgFEM is not very efficient, unless you want to deal with plastic
https://www.imechanica.org/comment/28895#comment-28895
<a id="comment-28895"></a>
<p><em>In reply to <a href="https://www.imechanica.org/comment/28894#comment-28894">Gaussianity</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>FEM is not the best way forward for rough contact. There are full 2D codes available public domain, including surface generators by Lars Pastewka in fact.</p>
<p><span>the contact mechanics calculator is here:</span></p>
<p><a href="http://contact.engineering/" rel="noreferrer" target="_blank" data-saferedirecturl="https://www.google.com/url?hl=en-GB&q=http://contact.engineering/&source=gmail&ust=1487425899196000&usg=AFQjCNF3eAz1KN-08LJK93FkuA4nJvgwgQ">http://contact.engineering/</a></p>
<p><span>You can find a rough surface generator here:</span></p>
<p><a href="https://gist.github.com/pastewka/72ab48e6570c72792a3cd0ff85d0e653" rel="noreferrer" target="_blank" data-saferedirecturl="https://www.google.com/url?hl=en-GB&q=https://gist.github.com/pastewka/72ab48e6570c72792a3cd0ff85d0e653&source=gmail&ust=1487425899197000&usg=AFQjCNE54qBff7LOkRmIg6aQVbe0_M9yDw">https://gist.github.com/pastewka/72ab48e6570c72792a3cd0ff85d0e653</a> </p>
<p>So you need to define a more interesting project!</p>
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</ul>Fri, 17 Feb 2017 13:52:42 +0000Mike Ciavarellacomment 28895 at https://www.imechanica.orgGaussianity
https://www.imechanica.org/comment/28894#comment-28894
<a id="comment-28894"></a>
<p><em>In reply to <a href="https://www.imechanica.org/comment/28891#comment-28891">Gaussianity</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p><span>Thank you sir, this addresses many of my doubts and as it happens my doubt on gaussianity, partly, was a result of thoughts on the first two papers you mentioned here. Correct me if I'm wrong, but from what I've seen from most of the papers that they address only the gaussianity because they are more concerned about the "qualitative" behaviour of the load-separtion & load-area relationships. </span></p>
<p><span>As I am new to this I am currently starting with a 1D roughness which is equivalent to the 2D isotropic rough as in papers by Popov and also in <a class="body" href="http://www.sciencedirect.com/science/article/pii/S0043164812003134" target="_blank">this 2013 paper by Scaraggi et al</a> and analyse it's contact with a plane surface using FEM. So, the questions on finding m2 and gaussianity. Thank you. </span></p>
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</ul>Fri, 17 Feb 2017 11:54:28 +0000Gouravarajucomment 28894 at https://www.imechanica.orgGaussianity
https://www.imechanica.org/comment/28891#comment-28891
<a id="comment-28891"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>The reason to insist on gaussianity is that the maths is much simpler. Most people are use to measure roughness assuming it is gaussian, and do not know much statistics. </p>
<p>In general, gaussian is the very reason of success of Greenwood-Williamson model: quite a few models before that assumed unrealistic asperity distributions, including a russian one assuming uniform distribution of which I forget the name. GW paper itself doesn't show a very good evidence of gaussianity of experimental surfaces, except perhaps the top of the distribution. This is discussed further in a recent paper of mine</p>
<p><a href="http://www.sciencedirect.com/science/article/pii/S0301679X16300858" data-clk="hl=en&sa=T&ct=res&cd=2&ei=YHamWIrmB4TDmAHXir7wAQ">On the effect of wear on <strong>asperity </strong>height distributions, and the corresponding effect in the mechanical response</a><a href="http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=2538233" data-clk="hl=en&sa=T&ct=res&cd=0&ei=YHamWIrmB4TDmAHXir7wAQ">On the significance of <strong>asperity </strong>models predictions of rough contact with respect to recent alternative theories</a>
</p><p>When the random processes appeared on the scene, the need to assume gaussianity became even more a condition for much easier mathematical development of Nayak and Longuet-Higgins. Again, this is vaguely based, as any gaussian distribution, on the Central Limit Theorem, which applies with a large number of independent process <strong>of about the same variance</strong>.</p>
<p>This last condition is not really easy to obtain from a fractal. In a typical fractal, you have essentially a Fourier series whose terms have different "size", and therefore CLT does not apply. Persson has made his entire career on the gaussian assumption because his model strongly assumes gaussianity. Notice that the original derivation of Persson's theory is very involute and takes 50 pages of physics journals, whereas I obtain it in two steps from a more mechanical procedure in</p>
<p><a href="http://www.sciencedirect.com/science/article/pii/S0301679X15003898" data-clk="hl=en&sa=T&ct=res&cd=3&ei=YHamWIrmB4TDmAHXir7wAQ">Rough contacts near full contact with a very simple <strong>asperity </strong>model</a>
</p><p>Yastrebov is right to show that to obtain gaussian fractals, you have to be very careful. Persson and co. have suggested "roll-off" component of PSD to increase the number of "nearly equal" component and get closer to CLT. But this is really a distraction and very difficult to understand if real surfaces really have a roll-off or not. Too much roll-off, and you have no longer a fractal! So you do need a very large window rather than roll-off, in your random surface, i.e. much larger than lower cutoff in wavenumber, and you should have a good gaussian surface.</p>
<p>But the question remains: are real surfaces gaussian? Some people now are starting to general Weibull fractals using RMD. I will explain later how to do that. This is mainly because of my papers above, especially in adhesion, which question this fuss about gaussianity.</p>
<p>Final remark: the fact that you have a power-law PSD does not imply you have a fractal. It may simply be a square-form signal whose Fourier decomposition gives a invese cubic power-law! You would beed to check the phases between different components, or higher-order autocorrelation functions.</p>
<p>Anyway, the sad part of this huge literature, it that it is really academic. The main point of GW is essentially showing the linearity of real contact area and load due to the fact that the number of contact spots increases with load in a way that both area and load grow proportionally. What Persson's theory found was generally quite academic improvement.</p>
<p>Is it a secret to explain what you are planning to do?</p>
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</ul>Fri, 17 Feb 2017 04:22:27 +0000Mike Ciavarellacomment 28891 at https://www.imechanica.orgAlso a query on insistence on Gaussianity of height distribution
https://www.imechanica.org/comment/28890#comment-28890
<a id="comment-28890"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>Thank you for the insight and the link. I was always confused by the interchanging use of Surface PSD and Profile PSD in many of the papers. This mostly clears up that aspect. Nayak's paper is indeed a bit tough to understand.</p>
<p>Why do most of the papers insist on the Gaussianity of height distribution? Like in <a class="field-item" href="https://arxiv.org/abs/1401.3800" target="_blank">this paper</a> by Yastrebov et al. they have a detailed discussion on how the lower and upper cut-off wavenumbers affect the Gaussianity of the surface. Is it because all the major asperity contact theories and Persson's theory consider the Gaussian rough surfaces or is their a practical aspect to this as well? Thank you.</p>
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</ul>Thu, 16 Feb 2017 21:43:30 +0000Gouravarajucomment 28890 at https://www.imechanica.orgthis is indeed a more subtle point
https://www.imechanica.org/comment/28888#comment-28888
<a id="comment-28888"></a>
<p><em>In reply to <a href="https://www.imechanica.org/comment/28887#comment-28887">Sir, Thank you so much for</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>The relation between profile and surface is not that obvious. I suspect many papers around make some mistake (possibly even Pastewka-Robbins one on which this post started!). In short, Nayak paper of 1971 explains it all, although it may not be the easiest. There is no problem with m0, but there is with m2 --- the slope has a factor 2 difference, because slope in x direction and slòpe in y-direction are independent uncorrelated processes see </p>
<p><a href="http://www.sciencedirect.com/science/article/pii/S0043164806000111" data-clk="hl=en&sa=T&ct=res&cd=0&ei=pBCmWPHDMZDVjAGv-ZvIAw">Some observations on Persson's diffusion theory of elastic contact</a></p>
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</ul>Thu, 16 Feb 2017 20:52:40 +0000Mike Ciavarellacomment 28888 at https://www.imechanica.orgSir, Thank you so much for
https://www.imechanica.org/comment/28887#comment-28887
<a id="comment-28887"></a>
<p><em>In reply to <a href="https://www.imechanica.org/comment/28884#comment-28884">question on PSD</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p><span>Sir, Thank you so much for the prompt reply. </span></p>
<p><span>I meant let's say,</span></p>
<p>a) we generate an isotropic rough surface using PSD and get the moments m2 and m4 by integrating the PSD.</p>
<p>b) Then after generating the rough surface, if we take an arbitrary profile of the surface and count the number of zeros and extrema and using the method mentioned in Longuet-Higgins' paper on isotropic rough surfaces caclulate the moments m2 and m4. </p>
<p>Will the values of m2 and m4 obtained by methods a) and b) match? Thank you.</p>
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</ul>Thu, 16 Feb 2017 20:37:48 +0000Gouravarajucomment 28887 at https://www.imechanica.orgquestion on PSD
https://www.imechanica.org/comment/28884#comment-28884
<a id="comment-28884"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>Sir, I don't understand your question. If you know PSD, you can integrate it to get the moments. Longuet-Higgins is a theory to study the maxima, minima, zero-crossings, no need to use that to compute m2 and m4. Please be precise.</p>
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</ul>Thu, 16 Feb 2017 19:29:58 +0000Mike Ciavarellacomment 28884 at https://www.imechanica.orgSpectral Moments of self-affine fractals
https://www.imechanica.org/comment/28880#comment-28880
<a id="comment-28880"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>Sir, when we are generating a self-affine fractal rough surface using the Power Spectral Density, does the Longuet-Higgins theory that "by counting the zeros and the extrema we can estimate the moments m2 and m4" still apply? Thank you. </p>
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</ul>Thu, 16 Feb 2017 15:24:05 +0000Gouravarajucomment 28880 at https://www.imechanica.orgPure coincidence DMT approx work in Pastewka-Robbins model?
https://www.imechanica.org/comment/28782#comment-28782
<a id="comment-28782"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>This paper may help shed some ligth why the very numerous crude approximations in PR model may have coincidentally led to reasonable agreement in their set of parameters. But not for any extrapolation fundamental purpose! The paper is submitted but probably siib accepted, as reviewers were positive.</p>
<p><span>1. </span><span class="list-identifier"><a title="Abstract" href="https://arxiv.org/abs/1701.04300">arXiv:1701.04300</a> [<a title="Download PDF" href="https://arxiv.org/pdf/1701.04300">pdf</a>, <a title="Download PostScript" href="https://arxiv.org/ps/1701.04300">ps</a>, <a title="Other formats" href="https://arxiv.org/format/1701.04300">other</a>]</span></p>
<p>On the use of DMT approximations in adhesive contacts, with remarks on random rough contacts<a href="https://arxiv.org/find/cond-mat/1/au:+Ciavarella_M/0/1/0/all/0/1">Michele Ciavarella</a><span class="descriptor">Comments:</span> 11 pages, 5 figures<span class="descriptor">Subjects:</span> <span class="primary-subject">Materials Science (cond-mat.mtrl-sci)</span></p>
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</ul>Wed, 18 Jan 2017 07:27:15 +0000Mike Ciavarellacomment 28782 at https://www.imechanica.orgthe deviation from GW model cannot be all due to scatter
https://www.imechanica.org/comment/28775#comment-28775
<a id="comment-28775"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>In this new paper accepted in Trib Int we show that the deviation from PR to GW cannot be all attributed to scatter due to imperfect tails of Gaussian surfaces as easily provoqued by low fractal dimension with insufficient size of the domain</p>
<p><span><a href="https://www.researchgate.net/publication/312153253_Adhesion_between_self-affine_rough_surfaces_possible_large_effects_in_small_deviations_from_the_nominally_Gaussian_case">https://www.researchgate.net/publication/312153253_Adhesion_between_self...</a></span></p>
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</ul>Sun, 08 Jan 2017 14:07:37 +0000Mike Ciavarellacomment 28775 at https://www.imechanica.orghere for example some comparison with experiments
https://www.imechanica.org/comment/28772#comment-28772
<a id="comment-28772"></a>
<p><em>In reply to <a href="https://www.imechanica.org/node/20731">On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces</a></em></p>
<div class="field field-name-comment-body field-type-text-long field-label-hidden"><div class="field-items"><div class="field-item even"><p>Despite these days it is impossible to talk of GW models because the "fractal" community suggests interaction and multiscale effects are completely wrong in GW, here are some GW models with adhesion which seem to work against experiments, showing the main effect of rms roughness, contrary to what the PR model says in the rush to forget all GW, that stickiness depends only on slopes and curvature <a href="https://www.researchgate.net/profile/Attilio_Frangi/publication/288056526_Evaluation_of_adhesion_in_microsystems_using_equivalent_rough_surfaces_modeled_with_spherical_caps/links/56b318c308aed7ba3fee0e3a.pdf mc">https://www.researchgate.net/profile/Attilio_Frangi/publication/28805652...</a></p>
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</ul>Sat, 07 Jan 2017 15:49:15 +0000Mike Ciavarellacomment 28772 at https://www.imechanica.org