iMechanica - crack growth
https://imechanica.org/taxonomy/term/834
enAnalytical Models for Fatigue Life Prediction of Metals in the Stress-Life Approach -- phd thesis by Pietro D’Antuono
https://imechanica.org/node/23693
<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/256">Fatigue</a></div><div class="field-item odd"><a href="/taxonomy/term/11616">sn curves</a></div><div class="field-item even"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item odd"><a href="/taxonomy/term/12659">variable amplitudes</a></div><div class="field-item even"><a href="/taxonomy/term/5180">notches</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 collegues</p>
<p> I'd be very grateful if you could have a look, if not a deep reading, at the phd thesis of my last student, playing on classical results on uniaxial fatigue, but with a view of simple, unified perspective on constant and varying amplitude fatigue. We made large use of e-fatigue.com web site and the data in there.<br clear="all" /> Thanks in advance for any remark. The final thesis will be submitted in few weeks time.</p>
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</div></div></div>Sat, 19 Oct 2019 18:49:58 +0000Mike Ciavarella23693 at https://imechanica.orghttps://imechanica.org/node/23693#commentshttps://imechanica.org/crss/node/23693On unified crack propagation laws
https://imechanica.org/node/23006
<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/256">Fatigue</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item even"><a href="/taxonomy/term/10019">Crack growth rate</a></div><div class="field-item odd"><a href="/taxonomy/term/12361">Short crack</a></div><div class="field-item even"><a href="/taxonomy/term/12362">Long crack</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><span>The anomalous propagation of short cracks shows generally exponential fatigue crack growth but the dependence on stress range at high stress levels is not compatible with Paris’ law with exponent m=2. Indeed, some authors have shown that the standard uncracked SN curve is obtained mostly from short crack propagation, assuming that the crack size a increases with the number of cycles N as da/dN=H\Delta\sigma^h where h is close to the exponent of the Basquin’s power law SN curve. We therefore propose a general equation for crack growth which for short cracks has the latter form, and for long cracks returns to the Paris’ law. We show generalized SN curves, generalized Kitagawa–Takahashi diagrams, and discuss the application to some experimental data. The problem of short cracks remains however controversial, as we discuss with reference to some examples.</span></p>
<p><a class="doi" title="Persistent link using digital object identifier" href="https://doi.org/10.1016/j.engfracmech.2018.12.023" rel="noreferrer noopener" target="_blank">https://doi.org/10.1016/j.engfracmech.2018.12.023</a> </p>
<p><span><span><a href="https://www.researchgate.net/publication/330342133_On_unified_crack_propagation_laws">https://www.researchgate.net/publication/330342133_On_unified_crack_prop...</a></span></span></p>
<p><span><span><a href="https://www.researchgate.net/profile/Antonio_Papangelo">https://www.researchgate.net/profile/Antonio_Papangelo</a></span></span></p>
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</div></div></div>Mon, 14 Jan 2019 13:54:42 +0000Antonio Papangelo23006 at https://imechanica.orghttps://imechanica.org/node/23006#commentshttps://imechanica.org/crss/node/23006Discussion of fracture paper #13 - Cohesive properties at ductile tearing
https://imechanica.org/node/19424
<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/6647">ductile</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item even"><a href="/taxonomy/term/7475">tearing</a></div><div class="field-item odd"><a href="/taxonomy/term/5169">thin plates</a></div><div class="field-item even"><a href="/taxonomy/term/10457">fracture processes</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>In this review of particularly readworthy papers in EFM, I have selected a paper about the tearing of large ductile plates, namely:</p>
<p><a href="http://www.sciencedirect.com/science/article/pii/S0013794415000958">”Cohesive zone modeling and calibration for mode I tearing of large ductile plates” by P.B. Woelke, M.D. Shields, J.W. Hutchinson, Engineering Fracture Mechanics, 147 (2015) 293-305.</a></p>
<p>The paper begins with a very nice review of the failure processes for plates with thicknesses from thick to thin, from plane strain fracture, via increasing amounts of strain localisation and failure along shear planes, to the thinnest foils that fail by pure strain localisation.</p>
<p>The plates in the title have in common that they contain a blunt notch and are subjected to monotonically increasing load. They are too thin to exclusively fracture and too thick to fail through pure plastic yielding. Instead the failure process is necking, followed by fracture along a worn-out slip plane in the necking region. Macroscopically it is mode I but on a microscale the final failure along a slip plane have the kinetics of mixed mode I and III and, I guess, also mode II. </p>
<p>A numerical solution of the problem resolving the details of the fracture process, should perhaps be conceivable but highly unpractical for engineering purposes. Instead, the necking region, which includes the strain localisation process and subsequent shear failure is a region of macroscopically unstable material and is modelled by a cohesive zone. The remaining plate is modelled as a power-law hardening continuum based on true stress and logarithmic strains.</p>
<p>The analysis is divided into two parts. First a cross-section perpendicular to the stretching of the cohesive zone is treated as a plane strain section. This is the cross section with a shape in which the parable with a neck becomes obvious. Here the relation between the contributions to the cohesive energy from strain localisation and from shear failure is obtained. A Gurson material model is used. Second, the structural scale model reveals the division of the tearing energy into the cohesive energy and the plastic dissipation outside the cohesive zone. The cohesive zone model accounts for a position dependent cohesive tearing energy and experimental results of B.C. Simonsen, R. Törnqvist, Marine Structures, vol. 17, pp. 1-27, 2004 are used to calibrate the cohesive energy.</p>
<p>It is found that the calibrated cohesive energy is low directly after initiation of crack growth, and later assumes a considerably higher steady state value. The latter is attained when the crack has propagated a distance of a few plate thicknesses away from the initial crack tip position. Calculations are continued until the crack has transversed around a third of the plate width.</p>
<p>I can understand that the situation during the initial crack growth is complex, as remarked by the investigators. I guess they would also agree that it would be better if the lower initial cohesive energy could be correlated to a property of the mechanical state instead of position. As the situation is, the position dependence seems to be the correct choise until it is figured out what happens in a real necking region</p>
<p>I wonder if the investigators continued computing the cohesive energy until the crack completely transversed the plate. That would provide an opportunity to test hypothesises both at initiation of crack growth and at the completed breaking of the plate. The situations that have some similarities but are still different would put the consistency of any hypothesis regarding dependencies of mechanical state to the test. </p>
<p>I am here taking the liberty to suggest other characteristics that may vary with the distance to the original crack tip position.</p>
<p>The strains across the cohesive zone are supposed to be large compared to the strains along it. This is the motivation for doing the plane strain calculations of the necking process. Could it be different in the region close to the original blunt crack tip where the situation is closer to plane stress than plane strain? The question is of course, if that influences the cohesive energy a distance of several plate thicknesses ahead of the initial crack position.</p>
<p>Another hypothesis could be that the compressive residual stress along the crack surface that develops as the crack propagate, influence the mechanical behaviour ahead of the crack tip. For very short necking regions the stress may even reach the yield limit in a thin region along the crack surface. Possibly that can have an effect on the stresses and strains in the necking region that affects the failure processes.</p>
<p>My final candidate for a hypothesis is the rotation that is very large at the crack tip before initiation of crack growth. In a linear elastic model and a small strain theory, rotation becomes unbounded before crack growth is initiated. A similar phenomenon has been reported by Lau, Kinloch, Williams and coworkers. The observation is that the severe rotation of the material adjacent to a bi-material adhesive lead to erroneous calibration of the cohesive energy. Could this be related to the lower cohesion energy? I guess that would mean that the resolution is insufficient in the area around the original crack tip position.</p>
<p>Are there any other ideas, or, even better, does anyone already have the answer to why the cohesive energy is very small immediately after initiation of crack growth?</p>
<p>Per Ståhle</p>
</div></div></div>Tue, 02 Feb 2016 20:12:29 +0000esis19424 at https://imechanica.orghttps://imechanica.org/node/19424#commentshttps://imechanica.org/crss/node/19424A well‐conditioned and optimally convergent XFEM for 3D linear elastic fracture
https://imechanica.org/node/19123
<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/31">fracture</a></div><div class="field-item odd"><a href="/taxonomy/term/418">xfem</a></div><div class="field-item even"><a href="/taxonomy/term/1088">3D</a></div><div class="field-item odd"><a href="/taxonomy/term/10857">global enrichment</a></div><div class="field-item even"><a href="/taxonomy/term/10858">conditioning</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item even"><a href="/taxonomy/term/10859">3d crack growth</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 href="http://onlinelibrary.wiley.com/doi/10.1002/nme.4982/full" data-clk="hl=en&sa=T&ct=res&cd=0&ei=PgBHVu-rAtSTmAHlhLjwCg">A well‐conditioned and optimally convergent <strong>XFEM </strong>for 3D linear elastic fracture</a>K <strong>Agathos</strong>, <a href="https://scholar.google.lu/citations?user=2n9Mwt8AAAAJ&hl=en&oi=sra">E <strong>Chatzi</strong></a>, <a href="https://scholar.google.lu/citations?user=QKZBZ48AAAAJ&hl=en&oi=sra">S <strong>Bordas</strong></a>… - International Journal for …, 2015 - Wiley Online LibrarySummary A variation of the extended finite element method for three-dimensional fracture <br />mechanics is proposed. It utilizes a novel form of enrichment and point-wise and integral <br />matching of displacements of the standard and enriched elements in order to achieve ...<a href="https://scholar.google.lu/scholar?cites=12930320536690086955&as_sdt=2005&sciodt=0,5&hl=en">Cited by 2</a> <a class="gs_nph" href="https://scholar.google.lu/scholar?hl=en&q=bordas+chatzi+agathos+XFEM&btnG=&as_sdt=1%2C5&as_sdtp=#">Cite</a> <span class="gs_nph"><a id="gs_svs0" href="https://scholar.google.lu/citations?view_op=view_citation&continue=/scholar%3Fq%3Dbordas%2Bchatzi%2Bagathos%2BXFEM%26hl%3Den%26as_sdt%3D0,5&citilm=1&citation_for_view=QKZBZ48AAAAJ:B9dQ7Cd3MGsC&hl=en&oi=saved">Saved</a></span>
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<p><a href="http://orbiluuni.porwait.com/bitstream/10993/21427/1/presentation.pdf" data-clk="hl=en&sa=T&oi=gga&ct=gga&cd=1&ei=PgBHVu-rAtSTmAHlhLjwCg"><span class="gs_ggsS">porwait.com <span class="gs_ctg2">[PDF]</span></span></a><span class="gs_ctc"><span class="gs_ct1">[PDF]</span></span> <a href="http://orbiluuni.porwait.com/bitstream/10993/21427/1/presentation.pdf" data-clk="hl=en&sa=T&oi=ggp&ct=res&cd=1&ei=PgBHVu-rAtSTmAHlhLjwCg"><strong>XFEM </strong>with global enrichment for 3D cracks</a>K <strong>Agathos</strong>, <a href="https://scholar.google.lu/citations?user=2n9Mwt8AAAAJ&hl=en&oi=sra">E <strong>Chatzi</strong></a>, <a href="https://scholar.google.lu/citations?user=QKZBZ48AAAAJ&hl=en&oi=sra">S <strong>Bordas</strong></a>, D Talaslidis - 2015 - orbiluuni.porwait.comAbstract:[en] We present an extended finite element method (XFEM) based on fixed area <br />enrichment which 1) suppresses the difficulties associated with ill-conditioning, even for" <br />large" enrichment radii; 2) requires 50 times fewer enriched degrees of freedom (for a ...<a class="gs_nph" href="https://scholar.google.lu/scholar?hl=en&q=bordas+chatzi+agathos+XFEM&btnG=&as_sdt=1%2C5&as_sdtp=#">Cite</a> <span class="gs_nph"><a id="gs_svs1" href="https://scholar.google.lu/citations?view_op=view_citation&continue=/scholar%3Fq%3Dbordas%2Bchatzi%2Bagathos%2BXFEM%26hl%3Den%26as_sdt%3D0,5&citilm=1&citation_for_view=QKZBZ48AAAAJ:cjqyVjQpDKAC&hl=en&oi=saved">Saved</a></span> <a class="gs_mor" href="https://scholar.google.lu/scholar?hl=en&q=bordas+chatzi+agathos+XFEM&btnG=&as_sdt=1%2C5&as_sdtp=#">More</a>
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<p><a href="http://orbilu.uni.lu/bitstream/10993/21427/3/s1-ln1947897895844769-1939656818Hwf-354338224IdV-177318626419478978PDF_HI0001%283%29.pdf" data-clk="hl=en&sa=T&oi=gga&ct=gga&cd=2&ei=PgBHVu-rAtSTmAHlhLjwCg"><span class="gs_ggsS">uni.lu <span class="gs_ctg2">[PDF]</span></span></a><a href="http://orbilu.uni.lu/handle/10993/21427" data-clk="hl=en&sa=T&ct=res&cd=2&ei=PgBHVu-rAtSTmAHlhLjwCg"><strong>XFEM </strong>with global enrichment for 3D crack growth</a>K <strong>Agathos</strong>, <a href="https://scholar.google.lu/citations?user=2n9Mwt8AAAAJ&hl=en&oi=sra">E <strong>Chatzi</strong></a>, <a href="https://scholar.google.lu/citations?user=QKZBZ48AAAAJ&hl=en&oi=sra">S <strong>Bordas</strong></a>… - … Numerical Analysis Week, 2015 - orbilu.uni.luAbstract:[en] We present an extended finite element method (XFEM) based on fixed area <br />enrichment which 1) suppresses the difficulties associated with ill-conditioning, even for" <br />large" enrichment radii; 2) requires 50 times fewer enriched degrees of freedom (for a ...<a class="gs_nph" href="https://scholar.google.lu/scholar?hl=en&q=bordas+chatzi+agathos+XFEM&btnG=&as_sdt=1%2C5&as_sdtp=#">Cite</a> <span class="gs_nph"><a id="gs_svs2" href="https://scholar.google.lu/citations?view_op=view_citation&continue=/scholar%3Fq%3Dbordas%2Bchatzi%2Bagathos%2BXFEM%26hl%3Den%26as_sdt%3D0,5&citilm=1&citation_for_view=QKZBZ48AAAAJ:w_dVLYmSw0MC&hl=en&oi=saved">Saved</a></span>
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<p><a href="http://orbilu.uni.lu/bitstream/10993/22331/2/paper.pdf" data-clk="hl=en&sa=T&oi=gga&ct=gga&cd=3&ei=PgBHVu-rAtSTmAHlhLjwCg"><span class="gs_ggsS">uni.lu <span class="gs_ctg2">[PDF]</span></span></a><span class="gs_ctc"><span class="gs_ct1">[CITATION]</span></span> <a href="http://orbilu.uni.lu/handle/10993/22331" data-clk="hl=en&sa=T&ct=res&cd=3&ei=PgBHVu-rAtSTmAHlhLjwCg">Stable 3D extended finite elements with higher order enrichment for accurate non planar fracture</a>K <strong>Agathos</strong>, <a href="https://scholar.google.lu/citations?user=2n9Mwt8AAAAJ&hl=en&oi=sra">E <strong>Chatzi</strong></a>, <a href="https://scholar.google.lu/citations?user=QKZBZ48AAAAJ&hl=en&oi=sra">S <strong>Bordas</strong></a> - Computer Methods in Applied …, 2015 - orbilu.uni.luAbstract We present an extended finite element method (XFEM) for 3D non-planar linear <br />elastic fracture. The new approach not only provides optimal convergence using geometrical <br />enrichment but also enables to contain the increase in conditioning number characteristic ...<a class="gs_nph" href="https://scholar.google.lu/scholar?hl=en&q=bordas+chatzi+agathos+XFEM&btnG=&as_sdt=1%2C5&as_sdtp=#">Cite</a> <span class="gs_nph"><a id="gs_svs3" href="https://scholar.google.lu/citations?view_op=view_citation&continue=/scholar%3Fq%3Dbordas%2Bchatzi%2Bagathos%2BXFEM%26hl%3Den%26as_sdt%3D0,5&citilm=1&citation_for_view=QKZBZ48AAAAJ:w2v21TepJGQC&hl=en&oi=saved">Saved</a></span>
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<p><a href="http://publications.uni.lu/bitstream/10993/19960/1/s1-ln1947897895844769-1939656818Hwf-354338224IdV-177318626419478978PDF_HI0001%283%29.pdf" data-clk="hl=en&sa=T&oi=gga&ct=gga&cd=4&ei=PgBHVu-rAtSTmAHlhLjwCg"><span class="gs_ggsS">uni.lu <span class="gs_ctg2">[PDF]</span></span></a><span class="gs_ctc"><span class="gs_ct1">[CITATION]</span></span> <a href="http://publications.uni.lu/handle/10993/19960" data-clk="hl=en&sa=T&ct=res&cd=4&ei=PgBHVu-rAtSTmAHlhLjwCg">Extended Finite Element Method with Global Enrichment</a>K <strong>Agathos</strong>, <a href="https://scholar.google.lu/citations?user=2n9Mwt8AAAAJ&hl=en&oi=sra">E <strong>Chatzi</strong></a>, <a href="https://scholar.google.lu/citations?user=QKZBZ48AAAAJ&hl=en&oi=sra">S <strong>Bordas</strong></a>… - International Journal for …, 2015 - publications.uni.luDate Submitted by the Author: n/a <strong> ...</strong> Complete List of Authors: <strong>Agathos</strong>, Konstantinos; Aristotle <br /> University Thessaloniki, Civil Engineering <strong>Chatzi</strong>, Eleni; ETH Zurich, <strong>Bordas</strong>, Stéphane PA; Cardiff <br /> University, Institute of Mechanics & Advanced Materials Talaslidis, Demosthenes; <strong> ...</strong><a href="https://scholar.google.lu/scholar?q=related:o-4_0FDg0uUJ:scholar.google.com/&hl=en&as_sdt=0,5">Related articles</a> <a class="gs_nph" href="https://scholar.google.lu/scholar?cluster=16560545417490591395&hl=en&as_sdt=0,5">All 4 versions</a> <a class="gs_nph" href="https://scholar.google.lu/scholar?hl=en&q=bordas+chatzi+agathos+XFEM&btnG=&as_sdt=1%2C5&as_sdtp=#">Cite</a> <span class="gs_nph"><a id="gs_svs4" href="https://scholar.google.lu/citations?view_op=view_citation&continue=/scholar%3Fq%3Dbordas%2Bchatzi%2Bagathos%2BXFEM%26hl%3Den%26as_sdt%3D0,5&citilm=1&citation_for_view=QKZBZ48AAAAJ:FlNF6OXwGF0C&hl=en&oi=saved">Saved</a></span>
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<p><a href="http://orbilu.uni.lu/bitstream/10993/22289/1/igabem3d_01doubleSpace.pdf" data-clk="hl=en&sa=T&oi=gga&ct=gga&cd=5&ei=PgBHVu-rAtSTmAHlhLjwCg"><span class="gs_ggsS">uni.lu <span class="gs_ctg2">[PDF]</span></span></a><a href="http://orbilu.uni.lu/handle/10993/22289" data-clk="hl=en&sa=T&ct=res&cd=5&ei=PgBHVu-rAtSTmAHlhLjwCg">Isogeometric boundary element methods for three dimensional fatigue crack growth</a>X Peng, <a href="https://scholar.google.lu/citations?user=Tf2Yn5EAAAAJ&hl=en&oi=sra">E Atroshchenko</a>, P Kerfriden, <a href="https://scholar.google.lu/citations?user=QKZBZ48AAAAJ&hl=en&oi=sra">S <strong>Bordas</strong></a> - 2015 - orbilu.uni.lu
</p><p>Abstract:[en] The isogeometric boundary element method (IGABEM) based on NURBS is <br />adopted to model fracture problem in 3D. The NURBS basis functions are used in both crack</p>
</div></div></div>Sat, 14 Nov 2015 16:08:05 +0000Stephane Bordas19123 at https://imechanica.orghttps://imechanica.org/node/19123#commentshttps://imechanica.org/crss/node/19123An experimental/numerical investigation into the main driving force for crack propagation in uni-directional fibre-reinforced composite laminae
https://imechanica.org/node/17206
<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/31">fracture</a></div><div class="field-item odd"><a href="/taxonomy/term/2213">composite</a></div><div class="field-item even"><a href="/taxonomy/term/10100">lamina</a></div><div class="field-item odd"><a href="/taxonomy/term/418">xfem</a></div><div class="field-item even"><a href="/taxonomy/term/4829">orthotropic</a></div><div class="field-item odd"><a href="/taxonomy/term/651">enrichment</a></div><div class="field-item even"><a href="/taxonomy/term/10101">discontinuity</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item even"><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 href="http://hdl.handle.net/10993/12316">http://hdl.handle.net/10993/12316</a></p>
<p>This paper presents an enriched finite element method to simulate the growth of cracks in linear elastic, aerospace composite materials. The model and its discretisation are also validated through a complete experimental test series. Stress intensity factors are calculated by means of an interaction integral. To enable this, we propose application of (1) a modified approach to the standard interaction integral for heterogeneous orthotropic materials where material interfaces are present; (2) a modified maximum hoop stress criterion is proposed for obtaining the crack propagation direction at each step, and we show that the “standard” maximum hoop stress criterion which had been frequently used to date in literature, is unable to reproduce experimental results. The influence of crack description, material orientation along with the presence of holes and multi-material structures are investigated. It is found, for aerospace composite materials with View the MathML source ratios of approximately 10, that the material orientation is the driving factor in crack propagation. This is found even for specimens with a material orientation of 90°, which were previously found to cause difficulty in both damage mechanics and discrete crack models e.g. by the extended finite element method (XFEM). The results also show the crack will predominantly propagate along the fibre direction, regardless of the specimen geometry, loading conditions or presence of voids.</p>
</div></div></div>Sun, 21 Sep 2014 09:56:37 +0000Stephane Bordas17206 at https://imechanica.orghttps://imechanica.org/node/17206#commentshttps://imechanica.org/crss/node/17206VAL2015 conference on Variable Amplitude Loading - Abstract submission system opened
https://imechanica.org/node/16744
<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/74">conference</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/256">Fatigue</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item even"><a href="/taxonomy/term/2265">variable amplitude loading</a></div><div class="field-item odd"><a href="/taxonomy/term/5954">minisymposium</a></div><div class="field-item even"><a href="/taxonomy/term/7822">multiaxial fatigue</a></div><div class="field-item odd"><a href="/taxonomy/term/9883">random loading</a></div><div class="field-item even"><a href="/taxonomy/term/9884">fatigue design</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 iMechanician
</p>
<p>
We are preparing everything necessary to host the <strong>3rd</strong> <strong>International Conference on Material and Component Performance under Variable Amplitude Loading</strong> (VAL 2015) in <strong>Prague</strong>, Czech Republic in <strong>March 23-26, 2015</strong>. From now on, you can register your abstracts in the <a href="http://www.czech-in.org/cmGateway/VAL2015/abstractsubmission">online<br />
submission system</a>. The system will stay open till July 7, 2014, so do not forget to insert your abstract in time.
</p>
<p>
I wanted to highlight moreover a questionnaire, which we published on the conference website - see <a href="http://val-conf.org/minisymposia-inquiry.htm" target="_blank">http://val-conf.org/minisymposia-inquiry.htm</a>. It relates to our effort to support also less formal discussions through organizing the minisymposia. We hope they could be the right place to discuss various issues, uncertainties, etc. Anyhow, we need to know that there is a real interest in the individual topics, and that there are also researchers able to chair them. I'll refer here to one impotant item among the rules: "The chairman post is very important – as such, if more than 10 participants will register, he/she will be exempted from paying the participation fee for VAL 2015 conference."
</p>
<p>
Because we really need this feedback from potential participants, we decided to run the questionnaire as a contest. Those who fill the inquiry will get to the lottery, where 3 books of Prof. Jaap Schijve (Fatigue of Structures and Materials, Springer 2009) will be drawn as the main prize. The questionnaire will be closed also on July 7, 2014.
</p>
<p>
Best regards,
</p>
<p>
Jan Papuga & Milan Růžička
</p>
<p>
Chairmen of VAL2015
</p>
</div></div></div>Fri, 06 Jun 2014 12:01:27 +0000pragtic16744 at https://imechanica.orghttps://imechanica.org/node/16744#commentshttps://imechanica.org/crss/node/16744Research Associate - Modelling of Crack Growth under Fatigue-Oxidation Conditions
https://imechanica.org/node/15282
<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/73">job</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/256">Fatigue</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item even"><a href="/taxonomy/term/6546">oxidation</a></div><div class="field-item odd"><a href="/taxonomy/term/9082">nickel alloys</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 Research Associate is required to undertake an EPSRC-funded project to model oxidation damage at a crack tip and associated crack growth for nickel alloys.
</p>
<p>
You will join the vibrant Mechanics of Advanced Materials group at Loughborough (<a href="http://www.lboro.ac.uk/moam">www.lboro.ac.uk/moam</a>) which has gained significant experience in the study of mechanical behaviour of advanced materials.
</p>
<p>
You will have a good honours degree or Master or PhD (or equivalent) in Solid Mechanics /Mechanical Engineering/Applied Mathematics or other relevant discipline. Some experience and a good understanding of plasticity, micro-mechanics, fracture mechanics, fatigue, creep and diffusion are essential. Experience of modelling of micro-plasticity and mass diffusion is desirable.
</p>
<p>
For more details and to apply, please go to: <a href="http://www.jobs.ac.uk/job/AHD327/research-associate-in-model-oxidation/">http://www.jobs.ac.uk/job/AHD327/research-associate-in-model-oxidation/</a>
</p>
</div></div></div>Tue, 10 Sep 2013 15:50:33 +0000liguozhao15282 at https://imechanica.orghttps://imechanica.org/node/15282#commentshttps://imechanica.org/crss/node/15282Crack propagation in ANSYS vs. ABAQUS
https://imechanica.org/node/14345
<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/834">crack growth</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>Hello dear friends,</strong>
</p>
<p>
</p>
<p>
<strong>I am Morteza, PhD student of Materials Eng. I have this course of Computational Modelling with Abaqus this semester. My Professor asked me to compare different </strong><strong><strong>approaches of</strong> crack growth analysis in Ansys and Abaqus including different formulations, procedures,... . He recommended to check the user's manual in these two softwares.</strong>
</p>
<p>
<em><strong>I would like to appreciate it if anybody could help me with this task as I am absolutely new in this field.</strong></em>
</p>
<p>
</p>
<p>
<strong>Regards,</strong>
</p>
<p>
<strong>Morteza<br /></strong>
</p>
</div></div></div>Thu, 14 Mar 2013 09:17:54 +0000morteza201314345 at https://imechanica.orghttps://imechanica.org/node/14345#commentshttps://imechanica.org/crss/node/14345modelling the crack in Abaqus
https://imechanica.org/node/13539
<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/32">fracture mechanics</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</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>
Hi colleage
</p>
<p>
I am working on fracture mechanics recently and i am using Abaqus to do it, i am a new user in this software so i have some problems, in getting results and ... i want to get some variable such as J-integral, S.iF, number of cycles and ... but unfortunatelly i donno how to get it .
</p>
<p>
i want to ask if anybody can send me a sample of abaqus in this srea, then i can study and practise according to it and after that i can go through my project.
</p>
<p>
</p>
<p>
this is my email: <a href="mailto:mahyar.iii@gmail.com">mahyar.iii@gmail.com</a>
</p>
<p>
Thank you very much for your help.
</p>
</div></div></div>Tue, 30 Oct 2012 10:57:26 +0000mahyar13539 at https://imechanica.orghttps://imechanica.org/node/13539#commentshttps://imechanica.org/crss/node/13539Journal Club Theme of August 2012: Mesh-Dependence in Cohesive Element Modeling
https://imechanica.org/node/12899
<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/395">cohesive zone model</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item even"><a href="/taxonomy/term/879">cohesive element</a></div><div class="field-item odd"><a href="/taxonomy/term/4134">convergence</a></div><div class="field-item even"><a href="/taxonomy/term/5999">mesh dependence</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>
The classical cohesive zone theory of fracture finds its origins in the pioneering works by Dugdale, Barenblatt and Rice [1–3]. In their work, fracture is regarded as a progressive phenomenon in which separation takes place across a cohesive zone ahead of the crack tip and is resisted by cohesive tractions. Cohesive zone models are widely adopted by scientists and engineers perhaps due to their straightforward implementation within the traditional finite element framework. Some of the mainstream technologies proposed to introduce the cohesive theory of fracture into finite element analysis are the eXtended Finite Element Method (X-FEM) and cohesive elements.
</p>
<p>
Sukumar et al. [4] first utilized the X-FEM for modeling 3D crack growth by adding a discontinuous function and the asymptotic crack tip field to the finite elements. Subsequently, the method was extended to account for cohesive cracks [5]. While the X-FEM approach can deal with arbitrary crack paths, it becomes increasingly complicated for problems involving pervasive fracture and fragmentation.
</p>
<p>
On the other hand, the cohesive element approach consists on the insertion of cohesive finite elements along the edges or faces of the 2D or 3D mesh correspondingly [6-9]. Even though this approach is well suited for problems involving pre-defined crack directions, a number of known issues affect its accuracy when dealing with simulations including arbitrary crack paths, e.g., problems with the propagation of elastic stress waves (artificial compliance), spurious crack tip speed effects (lift-off), and mesh dependent effects (c.f. [10] for a complete review). However, the robustness of the method makes it one of the most common approaches for pervasive fracture and fragmentation analysis.
</p>
<p>
Artificial compliance and lift-off effects can be avoided by using an initially rigid cohesive law [8] or, more elegantly, a discontinuous Galerkin formulation with an activation criterion for cohesive elements [11,12]. However, the problem of mesh dependency, more precisely mesh-induced anisotropy and mesh-induced toughness, is an active area of research.
</p>
<p>
When a mesh is introduced to represent the continuum fracture problem within the cohesive element formulation, a constraint is introduced into the problem due to the inability of the mesh to represent the shape of an arbitrary crack. If we think of an arbitrary crack as a rectifiable path (2D) or surface (3D), the ability of a mesh to represent a straight line (2D) or plane (3D) as the mesh is refined is a necessary condition for the convergence of the cohesive element approach [14]. In 2-dimensional problems, the ability of a mesh to represent a straight segment is characterized by the path deviation ratio, defined as the ratio between the shortest path on the mesh edges connecting two nodes, and the Euclidian distance between them (see Fig. 1a). It is desirable, then, for the path deviation ratio to be independent on the segment direction (to avoid mesh-induced anisotropy) and to tend to one as the mesh size tends to zero (to avoid, in the limit, mesh-induced toughness). A mesh that satisfies these requirements is said to be isoperimetric.
</p>
<p>
[img_assist | nid=12896 | title=Figure 1 | desc=(a) 4k mesh, (b) 4k mesh with nodal perturbation, (c) K-Means mesh, and (d) Conjugate-Directions mesh. In all meshes, the path deviation ratio is defined as the ratio between the length of the red solid line and the blue dashed line. | link=none | align=center | width=640 | height=480]
</p>
<p>
The work of Radin and Sadun [13] shows that the pinwheel tiling of the plane has the isoperimetric property. Based on this result, Papoulia et al. [14] observed that crack paths obtained from pinwheel meshes are more stable as the meshes are refined compared to other types of meshes. It is worth noting, however, that pinwheel meshes are hard to generate and there is no known extension to the 3-dimensional case. In a recent work, Paulino et al. [15] analyzed the behavior of 4k meshes modified by nodal perturbation and edge swap operators (see Fig. 1b). Their results show that the expected value of the path deviation ratio (over all possible directions) is decreased for a given mesh size. It is worth noting, however, that even though the mesh induced-toughness is reduced in this way, the meshes under consideration still exhibit a considerable anisotropy [16].
</p>
<p>
Recently, K-Means meshes generated by the application of Delaunay’s triangulation to nodes resulting from clustering random points (see Fig. 1c), have been proposed as a way of alleviating mesh-induced anisotropy while keeping acceptable triangle quality [16]. For reasonable mesh sizes, K-Means meshes exhibit the same mean value of the path deviation ratio as 4k meshes with nodal perturbation while being perfectly isotropic. In the same article, another type of mesh termed Conjugate-Directions mesh is introduced. Conjugate-Directions meshes are generated by the application of barycentric subdivision to K-Means meshes as depicted in Fig. 1d. In this way, the barycentric subdivision adds new directions to the existing K-Means mesh which tend to be orthogonal to the original directions as the K-Means tends to be smoother (i.e., as the K-Means algorithm is applied over a larger number of random points). This can be interpreted as enriching the set of directions provided by the original mesh with new conjugate directions. Consequently, Conjugate-Directions meshes exhibit the same isotropy observed in K-Means meshes while producing a drastically reduced mean value of the path deviation ratio for identical mesh sizes. Figure 2 shows the polar plot of the path deviation ratio vs. mesh direction for 4k, K-Means and Conjugate-Directions meshes.
</p>
<p>
</p>
<p>
[img_assist | nid=12897 | title=Figure 2 | desc= Polar plot of the path deviation ratio (minus 1) as a function of the mesh direction for the meshes under consideration. |<br />
link=none | align=center | width=352 | height=264]
</p>
<p>
</p>
<p>
Moreover, preliminary results show that the convergence of K-Means meshes in the sense of the mean value of the path deviation ratio is similar to that of 4k meshes as the mesh size is reduced [17], see Fig 3a. At the same time, the standard deviation decreases at a fastest rate when compared to 4k meshes as shown in Fig. 3b. However, numerical evidence shows that the path deviation ratio tends to saturate around 1.04 for both meshes. On the other hand, the same numerical experiment shows no indication of saturation for Conjugate-Directions meshes in the studied range of mesh-sizes. In summary, K-Means meshes are isotropic thus not providing preferred crack propagation directions. In addition to being isotropic, Conjugate-Directions meshes exhibit a better convergence behavior in the sense of the path deviation ratio, making them good candidates for cohesive element analysis of crack propagation problems where the crack path is not known a priori.
</p>
<p>
</p>
<p>
[img_assist | nid=12898 | title=Figure 3 | desc=convergence of the path deviation ratio; (a) its mean value, and (b) its standard deviation. |<br />
link=none | align=center | width=640 | height=480]
</p>
<p>
</p>
<p>
To conclude, we should emphasize that even though convergence in the sense of the path deviation ratio is a necessary condition for convergence of the cohesive element formulation, when dealing with finite meshes an occasional misalignment of an edge in the cohesive crack might be enough to cause the simulated crack path to diverge from the physical one. Needless to say, the issue of crack path convergence in the cohesive element formulation is still an open problem. The hope of many of the previously mentioned research efforts is that arbitrary crack propagation can be achieved through mesh design (pre-processing).
</p>
<p>
</p>
<p>
<strong>References</strong></p>
<p>[1] Dugdale, D. S., “Yielding of steel sheets containing slits,” Journal of the Mechanics and Physics of Solids, Vol. 8, No. 2, 1960, pp. 100–104.<br />
[2] Barenblatt, G. I., “The Mathematical Theory of Equilibrium Cracks in Brittle Fracture,” Advances in Applied Mechanics, Vol. 7, 1962, pp. 55–129.<br />
[3] Rice, J. R., “Mathematical analysis in the mechanics of fracture,” Fracture: an advanced treatise, Vol. 2, 1968, pp. 191– 311.<br />
[4] Sukumar, N., Moes, N., Moran, B. and Belytschko, T., “Extended finite element method for three-dimensional crack modeling,” International Journal for Numerical Methods in Engineering, Vol. 48, 2000, pp. 1549-1570.<br />
[5] Moes, N. and Belytschko, T., “Extended ﬁnite element method for cohesive crack growth,” Engineering Fracture Mechanics, Vol. 69, 2002, pp. 813-833.<br />
[6] Xu, X. P. and Needleman, A., “Numerical simulations of fast crack growth in brittle solids,” Journal of the Mechanics and Physics of Solids, Vol. 42, 1994, pp. 1397–1397.<br />
[7] Xu, X. P. and Needleman, A., “Numerical simulations of dynamic crack growth along an interface,” International Journal of Fracture, Vol. 74, 1995, pp. 289–324.<br />
[8] Camacho, G. T. and Ortiz, M., “Computational modeling of impact damage in brittle materials,” International Journal of Solids and Structures, Vol. 33, 1996, pp. 2899–2938.<br />
[9] Ortiz, M. and Pandolfi, A., “Finite-deformation irreversible cohesive elements for three-dimensional crack-propagation analysis,” International Journal for Numerical Methods in Engineering, Vol. 44, No. 9, 1999, pp. 1267–1282.<br />
[10] Seagraves, A. and Radovitzky, R., Advances in cohesive zone modeling of dynamic fracture, Springer Verlag, 2009.<br />
[11] Noels, L. and Radovitzky, R., “An explicit discontinuous Galerkin method for non-linear solid dynamics: Formulation, parallel implementation and scalability properties,” International Journal for Numerical Methods in Engineering, Vol. 74, 2008, pp. 1393-1420.<br />
[12] Radovitzky, R., Seagraves, A., Tupek, M., and Noels, L., “A scalable 3D fracture and fragmentation algorithm based on a hybrid, discontinuous Galerkin, cohesive element method,” Computer Methods in Applied Mechanics and Engineering, Vol. 200, No. 1-4, 2011, pp. 326-344.<br />
[13] Radin, C. and Sadun, L., “The isoperimetric problem for pinwheel tilings,” Communications in Mathematical Physics, Vol. 177, No. 1, 1996, pp. 255–263.<br />
[14] Papoulia, K.D., Vavasis, S.A., and Ganguly, P., “Spatial convergence of crack nucleation using a cohesive finite-element model on a pinwheel-based mesh,” International Journal for Numerical Methods in Engineering, Vol. 67, No. 1, 2006, pp. 1-16.<br />
[15] Paulino, G. H., Park, K., Celes, W., and Espinha, R., “Adaptive dynamic cohesive fracture simulation using nodal perturbation and edge-swap operators,” International Journal for Numerical Methods in Engineering, Vol. 84, No. 11, 2010, pp. 1303–1343.<br />
[16] Rimoli, J. J., Rojas, J. J., and Khemani, F. N., “On the mesh dependency of cohesive zone models for crack propagation analysis,” in 53rd AIAA Structures, Structural Dynamics, and Materials and Conference, Honolulu, HI, 2012.<br />
[17] Rimoli, J. J. and Rojas, J. J., “Meshing strategies for the alleviation of mesh-induced effects in cohesive element models,” submitted. Preprint: <a href="http://arxiv.org/abs/1302.1161">http://arxiv.org/abs/1302.1161</a></p>
</div></div></div>Sat, 04 Aug 2012 04:33:59 +0000Julian J. Rimoli12899 at https://imechanica.orghttps://imechanica.org/node/12899#commentshttps://imechanica.org/crss/node/12899Mathematics of Crack growth
https://imechanica.org/node/12269
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><ol><li> How to find G (energy release rate) using wnuk's equation? by considering the fracture process zone explaining the assumptions and concept involved??</li>
<li>can anyone explain about : Eshelby's basic assumption for finding the change of displacement after the crack tip has moved a distance x? </li>
<li>How is the general form(equation) for singular parts of the stresses in the plane of the crack derived (explain the breif fundamentals) ?
<p> all these question are in reference to the book Micromechanics of defects in solids by toshio mura </p></li>
</ol><p>
</p>
<p>
</p>
<p>
</p>
</div></div></div><div class="field field-name-taxonomy-forums field-type-taxonomy-term-reference field-label-above"><div class="field-label">Forums: </div><div class="field-items"><div class="field-item even"><a href="/forum/109">Ask iMechanica</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Free Tags: </div><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/32">fracture mechanics</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item even"><a href="/taxonomy/term/7379">modellin of crack</a></div></div></div>Tue, 10 Apr 2012 18:52:50 +0000paragiitb12269 at https://imechanica.orghttps://imechanica.org/node/12269#commentshttps://imechanica.org/crss/node/12269Fatigue crack growth
https://imechanica.org/node/12205
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
Hi all,
</p>
<p>
</p>
<p>
I wanted to simulate fatigue crack growth in ls-dyna, obtain dK, crack tip stress fields. But I wanted to start from a simple model. I can't find any examples online, tutorial...
</p>
</div></div></div><div class="field field-name-taxonomy-forums field-type-taxonomy-term-reference field-label-above"><div class="field-label">Forums: </div><div class="field-items"><div class="field-item even"><a href="/forum/357">Computational Mechanics Forum</a></div></div></div><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-above"><div class="field-label">Free Tags: </div><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/256">Fatigue</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item even"><a href="/taxonomy/term/881">modelling and simulation</a></div><div class="field-item odd"><a href="/taxonomy/term/4888">ls-dyna</a></div></div></div>Sat, 31 Mar 2012 02:13:02 +0000Mary Pops12205 at https://imechanica.orghttps://imechanica.org/node/12205#commentshttps://imechanica.org/crss/node/12205International Conference on Fatigue Damage of Structural Materials IX 16-21 September 2012, Hyannis, MA, USA
https://imechanica.org/node/11121
<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/74">conference</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/314">corrosion</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item even"><a href="/taxonomy/term/1516">Abrasion</a></div><div class="field-item odd"><a href="/taxonomy/term/2006">residual stress</a></div><div class="field-item even"><a href="/taxonomy/term/2750">fatigue damage</a></div><div class="field-item odd"><a href="/taxonomy/term/5156">ALLOYS</a></div><div class="field-item even"><a href="/taxonomy/term/6546">oxidation</a></div><div class="field-item odd"><a href="/taxonomy/term/6640">structural metals</a></div><div class="field-item even"><a href="/taxonomy/term/6641">overload</a></div><div class="field-item odd"><a href="/taxonomy/term/6642">underload</a></div><div class="field-item even"><a href="/taxonomy/term/6643">arbitrary loading sequences</a></div><div class="field-item odd"><a href="/taxonomy/term/6644">service spectrum loads</a></div><div class="field-item even"><a href="/taxonomy/term/6645">combined HCF LCF</a></div><div class="field-item odd"><a href="/taxonomy/term/6646">elevated or cryogenic temperatures</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><span class="Apple-style-span">Call for Papers - deadline 9 December 2011</span></strong></p>
<p><strong><span class="Apple-style-span">Submit your abstract here: <a href="http://www.fatiguedamageconference.com ">www.fatiguedamageconference.com </a></span></strong></p>
<p><span class="Apple-style-span">We welcome poster and abstract submissions on the following topics:</span><br /><span class="Apple-style-span"><br /></span></p>
<ul><li><span class="Apple-style-span">Structural metals and alloys pertinent to the aerospace, marine, off-shore, power generation and land based transportation industries</span></li>
<li><span class="Apple-style-span">Novel experimental methods to characterise fatigue damage and crack growth</span></li>
<li><span class="Apple-style-span">Overload/underload, arbitrary loading sequences, service spectrum loads, combined HCF/LCF</span></li>
<li><span class="Apple-style-span">Residual stress effects on fatigue damage and crack growth, measurement of internal stresses</span></li>
<li><span class="Apple-style-span">Extreme environments, including the effects of corrosion, oxidation, abrasion, elevated or cryogenic temperatures</span></li>
<li><span class="Apple-style-span">Innovative theroretical approaches, computational and analytical methods</span></li>
<li><span class="Apple-style-span">Life prediction methodologies for structural metals and alloys</span></li>
<li><span class="Apple-style-span">Fatigue mechanisms in advanced alloys and metallic systems</span></li>
<li><span class="Apple-style-span">Micro-structurally short cracks</span></li>
</ul><p> </p>
<p><span class="Apple-style-span">Contributions relating to ceramics, nano-materials, construction materials (concrete), polymers (including rubber) and composites will not be considered for FDSM IX.</span></p>
</div></div></div>Thu, 22 Sep 2011 10:00:58 +0000Sophie Hayward11121 at https://imechanica.orghttps://imechanica.org/node/11121#commentshttps://imechanica.org/crss/node/11121Crack growth resistance versus projected crack length
https://imechanica.org/node/8967
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"></div></div></div><div class="field field-name-taxonomyextra field-type-taxonomy-term-reference field-label-above"><div class="field-label">Taxonomy upgrade extras: </div><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item even"><a href="/taxonomy/term/1349">J-R CURVE</a></div><div class="field-item odd"><a href="/taxonomy/term/2722">crack resistance curve</a></div><div class="field-item even"><a href="/taxonomy/term/5603">R curves</a></div></div></div>Fri, 24 Sep 2010 04:05:51 +0000Lucas Maximo Alves8967 at https://imechanica.orghttps://imechanica.org/node/8967#commentshttps://imechanica.org/crss/node/8967[SOLVED] 3D crack growth modelling in Abaqus by XFEM
https://imechanica.org/node/8402
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
Good day everyone,
</p>
<p>
I'm new to iMechanica and look forward to getting to know everyone here. <img src="modules/tinymce/includes/jscripts/tiny_mce/plugins/emotions/images/smiley-smile.gif" border="0" alt="Smile" title="Smile" /></p>
<p>
I'm currently doing analysis of interlaminar crack growth in fibre-reinforced composite by Extended Finite Element Method (XFEM) using Abaqus. I'm a new Abaqus user and therefore I have to familiarise myself by constructing random 2D and 3D models with isotropic materials before jumping onto anisotropic.
</p>
<p>
Having gone through a few tutorials by <a href="http://sites.google.com/site/matthewjpais/Home" title="Matthew Pais">Matthew Pais</a> (thank you), I've managed to successfully model a 2D crack propagation model. The crack seems to propagate like I intended it to and it's all good. But applying the same approach to construct a 3D model, the crack remains stationary even with the increase in load magnitude. I've also tried lowering down the Max Principal stress as well as Fracture Energy under Traction-Separation setting but to no avail. I always ended up with the error "too many attempts made for this increment".
</p>
<p>
Note that I'm using 100k as my increment number with initial 0.01, minimum 1E-09 and maximum 0.01.
</p>
<p>
So my questions are, what causes the error and how do I fix it? Are there any additional steps required for 3D crack growth propagation compared to 2D? Apart from the magnitude of the load and the Max Principal stress, are there any other parameters governing crack initiation and propagation in Abaqus?
</p>
<p>
I could provide the CAE or INP files if required. Any help is very much appreciated. Thanks in advance. <img src="modules/tinymce/includes/jscripts/tiny_mce/plugins/emotions/images/smiley-smile.gif" border="0" alt="Smile" title="Smile" /></p>
<p>
</p>
<p>
Regards,
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<p>
Yazri
</p>
</div></div></div><div class="field field-name-taxonomy-forums field-type-taxonomy-term-reference field-label-above"><div class="field-label">Forums: </div><div class="field-items"><div class="field-item even"><a href="/forum/666">Fracture Mechanics Forum</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Free Tags: </div><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/651">enrichment</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item even"><a href="/taxonomy/term/1088">3D</a></div><div class="field-item odd"><a href="/taxonomy/term/1320">XFEM crack propagation</a></div><div class="field-item even"><a href="/taxonomy/term/2201">XFEM in ABAQUS</a></div><div class="field-item odd"><a href="/taxonomy/term/5089">extended finite element method</a></div></div></div>Sun, 13 Jun 2010 13:36:33 +0000Yazri Yaakob8402 at https://imechanica.orghttps://imechanica.org/node/8402#commentshttps://imechanica.org/crss/node/8402R C Beams
https://imechanica.org/node/7265
<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/750">Beam</a></div><div class="field-item odd"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item even"><a href="/taxonomy/term/3182">concrete</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 align="justify">
I am a novice user of abaqus and trying to model crack growth in rc beams with longitudinal reinforcement and stirrups under dynamic loads by try and error method <img src="modules/tinymce/includes/jscripts/tiny_mce/plugins/emotions/images/smiley-tongue-out.gif" border="0" alt="Tongue out" title="Tongue out" /></p>
<p align="justify">
rebar layers are in shell element and i am using CDP for my concrete. i am trying to find out if i need to have many solid parts or one is enough and if mesh adaptivity is necessary or not because of crack growth <img src="modules/tinymce/includes/jscripts/tiny_mce/plugins/emotions/images/smiley-smile.gif" border="0" alt="Smile" title="Smile" />. I appreciate any consulting in this field and i will share my knowledge with anybody that helps me
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<p align="justify">
my first error message is
</p>
<p align="justify">
3479 nodes on an embedded element do not lie in any host element. Check coordinates, exterior tolerance and absolute exterior tolerance parameters, and the host element set definition. The nodes have been identified in node set ErrNodeEmbeddedNode.
</p>
<p align="justify">
maybe i missunderstand the definition of embedded region and need to revise in it<img src="modules/tinymce/includes/jscripts/tiny_mce/plugins/emotions/images/smiley-wink.gif" border="0" alt="Wink" title="Wink" />.
</p>
</div></div></div>Thu, 17 Dec 2009 21:34:05 +0000Reza Mousavi7265 at https://imechanica.orghttps://imechanica.org/node/7265#commentshttps://imechanica.org/crss/node/7265fatigue crack growth
https://imechanica.org/node/6996
<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/834">crack growth</a></div><div class="field-item odd"><a href="/taxonomy/term/3887">crack closure</a></div><div class="field-item even"><a href="/taxonomy/term/4494">similitude</a></div><div class="field-item odd"><a href="/taxonomy/term/4495">Region I growth</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 class="MsoNormal">
<span>Having glanced at the web site I can see that it might be useful to shed some light on fatigue crack growth and crack closure based concepts. </span>
</p>
<p><span> </span> <span>In the early 70’s Elber [1] hypothesised that the R ratio effect seen in constant amplitude fatigue tests was due to plasticity related crack closure and he presented an empirical formulation to account for this effect. Following this work a number of people have proposed that, for crack growth under constant amplitude loading, the concept of an opening stress intensity factor and crack closure is based on sound fundamental mechanics concepts. This methodology uses a <span>Δ</span>Keffecive (=Kmax - Kopen) versus da/dN curve that is (effectively) associated with constant amplitude load tests and is thought to coincide with the ΔK versus da/dN curve as measured at high R ratio (R > 0.7) tests. This approach thus rests on several assumptions, viz: that similitude is valid, that the<span> </span>crack closure hypothesis is valid and that the mechanisms associated with constant amplitude testing also holds for the problem of interest. It is further implicitly assumed that the physical process responsible for R ratio effects, as evidenced in experimental data, is due to crack closure and furthermore to crack closure alone. </span><span> </span> <span>With this in mind can I recommend that you read references [2, 3].<span> </span>The experimental data presented in these works reveal that the crack growth mechanisms under variable amplitude loading and those seen under constant amplitude loading differ. </span><span> </span> </p>
<p class="MsoNormal">
<span> These experimental results raise the question:</span>
</p>
<p><span> </span> <span>If closure is seen under constant amplitude tests does it mean it will hold under variable amplitude loading where the mechanisms of crack growth differ?</span> <span> </span> </p>
<p class="MsoNormal">
<span>Next consider the question: Is crack closure universal? </span>
</p>
<p><span> </span> <span>To address this question you need to read the paper by Forth, James, Johnston, and Newman [4]. Note that this is the same Newman who developed FASTRAN. This work reveals, and subsequently states, that crack closure does not apply to high strength aerospace steels. Reference [5] subsequently shows that crack closure does not apply to Mil Annealed Ti-6Al-4V.<span> </span>Reference [6] reveals that there were minimal R ratio effects in a rail locomotive steel. Hence closure didn’t apply for that particular steel. If you read the paper by Frost and Dugdale [7] you will see that the mild steel specimens tested in [8] also had (essentially) no R ratio effect and hence exhibited no closure. Thus experimental data reveals there are a number of materials for which closure does not apply.</span> <span> </span> </p>
<p class="MsoNormal">
<span> Consequently the answer to the questions is: No, the <em>crack closure hypothesis is not universal</em> even when the tests are constant amplitude fatigue tests. This does not mean that closure does not occur for some materials, just that the hypothesis is not universal.</span>
</p>
<p><span> </span> <span>Now read the presentation by Scott Forth at NASA [9]. <span> </span>Here NASA shows that the fatigue threshold ΔKth is a function of the test geometry, and as such is not unique. This means that the Region I crack growth law is a function of the test geometry. This, in turn, means that <em>similitude does not hold in Region I</em>. Indeed, for the D6ac steel considered in [8] and also in [4] Forth and Jones [9] have shown that crack growth in Regions I and II conforms to a non-similitude based growth law. </span><span> </span> </p>
<p class="MsoNormal">
<span>Since for practical problems we are dominantly interested in Region I crack growth (any design that starts off with crack growth in Region II will have a very short life!) this means that similitude can’t be routinely assumed in Region I. This finding also applies to non-aerospace materials, see [10] which reveals that crack growth in rail steels and Grade I ductile iron follows a non-similitude crack growth law. Thus Elber’s, Newman’s, Paris’, etc growth laws, which are all based on the concept of similitude,<span> </span>can’t be assumed to be valid in Region I.<span> </span></span>
</p>
<p><span> </span> <span>This begs the question: What happens if we use closure based laws to predict the growth of short cracks under representative in-service load spectra? To answer this question read the paper by Jones et al [11]. This paper shows that using FASTRAN, a closure based program developed by Newman, the predictions are out by a factor of approximately 7. Furthermore the predicted life is not conservative, i.e. the closure based prediction is 7 times too big.</span> <span> </span> </p>
<p class="MsoNormal">
<span> If we draw all of these experimental findings together we see that:</span>
</p>
<p><span> </span> <span><span>·<span> </span></span></span><span>The crack growth mechanisms under variable amplitude loading and those seen under constant amplitude loading differ. </span><span> </span> </p>
<p class="MsoNormal">
<span>(Thus the usefulness of constant amplitude da/dN versus ΔK data for addressing variable amplitude problems must be questioned.) </span>
</p>
<p><span> </span> <span><span>·<span> </span></span></span><span>The experimental data reveals that crack closure is not universal. </span><span> </span> </p>
<p class="MsoNormal">
<span><span> ·<span> </span></span></span><span>The assumption that the physical process responsible for R ratio effects is due to crack closure and furthermore to crack closure alone has not been universally established.</span>
</p>
<p><span> </span> <span><span>·<span> </span></span></span><span>Crack growth laws that are based on the concept of similitude can’t be assumed to be valid in Region I.<span> </span></span><span> </span> </p>
<p class="MsoNormal">
<span> So in summary, using similitude based laws to predict in-service growth of small cracks and hence the life of operational equipment should be avoided.</span>
</p>
<p><span> </span><span> </span><strong><span>REFERENCES</span></strong> </p>
<p class="MsoBodyText">
<span><span><span><span>[1]<span> </span></span></span><span>Elber W., The significance of fatigue crack closure, Damage Tolerance of Aircraft Structures, ASTM STP-486; 1971: 230-242.</span></span></span>
</p>
<p class="MsoNormal">
<span><span><span><span>[2]<span> </span></span></span><span>White P., Barter SA., and Molent L., Observations of crack path changes under simple variable amplitude loading in AA7050-T7451, Int. Journal of Fatigue,</span></span></span><span><span><span> 30, (2008) 1267–1278</span><span>.</span></span></span>
</p>
<p class="MsoBodyText">
<span><span><span>[3]<span> </span></span></span><span>Barter SA. and Wanhill R., Marker loads for quantitative fractography (QF) of fatigue in aerospace alloys, NLR-TR-2008-644, November 2008.</span></span>
</p>
<p class="MsoNormal" align="left">
<span><span><span>[4]<span> </span></span></span><span><span>Forth</span></span><span><span> S.C., James M.A., Johnston W.M., and Newman, J.C. Jr., Anomalous fatigue crack growth phenomena in high-strength steel, Proceedings Int. Congress on Fracture, Italy, 2007.</span></span></span>
</p>
<p class="MsoNormal">
<span><span><span>[5]<span> </span></span></span><span>Jones R., Farahmand B. and Rodopoulos</span></span><span><span><span> C.</span><span>, </span></span></span><span><span><span>Fatigue crack growth discrepancies</span></span></span><span><span><span> </span></span></span><span><span><span>with stress ratio</span><span>, Theoretical and Applied Fracture Mechanics, (2009), <span>Volume 51, Issue 1</span>, <span>pp 1-10.</span></span></span></span>
</p>
<p>
<span><span><span>[6]<span> </span></span></span><span>Jones R., Pitt S. and Peng D, The Generalised Frost–Dugdale approach to modelling fatigue crack growth, Engineering Failure Analysis, </span><span>Volume 15, (2008)</span><span>, <span>pp 1130-1149</span></span></span><span><span><span>.</span></span></span>
</p>
<p>
<span><span><span>[7]<span> </span></span></span><span>Frost N.E., Dugdale D.S., The propagation of fatigue cracks in test specimens, Journal Mechanics and Physics of Solids, 6, (1958), pp 92-110.</span><span> </span></span>
</p>
<p>
<span><span><span>[8]<span> </span></span></span><span>Forth SC., <span>The purpose of generating fatigue crack growth threshold data, </span><span>NASA</span><span> Johnson Space Center</span><span>, available on line at </span></span></span><a href="http://ntrs.nasa.gov/"><span><span>http://ntrs.nasa.gov/</span></span></a><span> </span>
</p>
<p>
<span><span><span>[9]<span> </span></span></span><span>Jones R. and Forth SC., Cracking in D6ac Steel, Proceedings International Conference on Fracture, </span><span><span>Ottawa</span></span><span><span>, 2009.</span></span><span> </span></span>
</p>
<p>
<span><span><span>[10]<span> </span></span></span><span>Jones R, Chen B. and Pitt S.,<span> </span>Similitude: cracking in steels, Theoretical and Applied Fracture Mechanics, <span>Volume 48, Issue 2</span>, (<span>2007)</span>, <span>pp 161-168.</span></span></span><span><span> </span></span>
</p>
<p class="MsoNormal" align="left">
<span><span>[11]<span> </span></span></span><span>Jones R., Molent L, and Pitt S., Crack growth from small flaws, International Journal of Fatigue, <span>Volume 29, (2007)</span>, pp<span> 1658-1667.</span></span><span> </span>
</p>
<p class="MsoNormal" align="left">
</p>
<p class="MsoNormal" align="left">
<span>By: </span><span>Rhys Jones and Susan Pitt </span>
</p>
</div></div></div>Wed, 28 Oct 2009 10:45:27 +0000jonesr6996 at https://imechanica.orghttps://imechanica.org/node/6996#commentshttps://imechanica.org/crss/node/6996Seeking candidates for positions in Houston, also positions in Germany
https://imechanica.org/node/2785
<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/73">job</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/211">reliability</a></div><div class="field-item odd"><a href="/taxonomy/term/248">finite element analysis</a></div><div class="field-item even"><a href="/taxonomy/term/834">crack growth</a></div><div class="field-item odd"><a href="/taxonomy/term/1870">heat transfer</a></div><div class="field-item even"><a href="/taxonomy/term/1966">low cycle fatigue</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>
Our agency, Reliability Analysis Associates, Inc., specializes in recruiting Reliability Engineers and related skills. For a client in the oil business in Houston, TX we are seeking candidates for two positions that require knowlege of finite element analysis, crack growth, reliability, and low cycle fatigue. The two job descriptions are attached.
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="Microsoft Office document icon" title="application/msword" src="/modules/file/icons/x-office-document.png" /> <a href="https://imechanica.org/files/Rel%20Eng%2C%20LM-RAA.doc" type="application/msword; length=39424" title="Rel Eng, LM-RAA.doc">Rel Eng, LM-RAA.doc</a></span></td><td>38.5 KB</td> </tr>
<tr class="even"><td><span class="file"><img class="file-icon" alt="Microsoft Office document icon" title="application/msword" src="/modules/file/icons/x-office-document.png" /> <a href="https://imechanica.org/files/Rel%20Eng%2C%20MD-RAA.doc" type="application/msword; length=40960" title="Rel Eng, MD-RAA.doc">Rel Eng, MD-RAA.doc</a></span></td><td>40 KB</td> </tr>
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</div></div></div>Sat, 01 Mar 2008 03:48:53 +0000Edward W. Walbridge2785 at https://imechanica.orghttps://imechanica.org/node/2785#commentshttps://imechanica.org/crss/node/2785Epi-convergence (max-ent bases), crack growth
https://imechanica.org/node/1215
<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/317">meshfree</a></div><div class="field-item odd"><a href="/taxonomy/term/833">epi-convergence</a></div><div class="field-item even"><a href="/taxonomy/term/834">crack growth</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>In the attached paper, we have used Variational Analysis techniques (in particular, the theory of epi-convergence) to prove the continuity of maximum-entropy basis functions. In general, for non-smooth functionals, moving objectives and/or constraints, the tools of Newton-Leibniz calculus (gradient, point-convergence) prove to be insufficient; notions of set-valued mappings, set-convergence, etc., are required. Epi-convergence bears close affinity to Gamma- or Mosco-convergence (widely used in the mathematical treatment of martensitic phase transformations). The introductory material on convex analysis and epi-convergence had to be omitted in the revised version; hence the material is by no means self-contained. Here are a few more pointers that would prove to be helpful. Our main point of reference is <a href="http://www.amazon.com/Variational-Analysis-Grundlehren-mathematischen-Wissenschaften/dp/3540627723" target="_blank">Variational Analysis by RTR and RJBW</a>; the Princeton Classic <a href="http://press.princeton.edu/titles/1815.html" target="_blank">Convex Analysis by RTR</a> provides the important tools in convex analysis. For convex optimization, the text <a href="http://www.stanford.edu/~boyd/cvxbook/" target="_blank">Convex Optimization by SB and LV (available online)</a> is excellent. The <a href="http://www.stanford.edu/~boyd/cvxbook/bv_cvxslides.pdf" target="_blank">lecture slides</a> provide a very nice (and gentle) introduction to some of the important concepts in convex analysis. The <a href="http://www.math.ucdavis.edu/~rjbw/ARTICLES/epinal.pdf" target="_blank">epigraphical landscape</a> is very rich, and many of the applications would resonate with mechanicians.</p>
<p> On a different topic (non-planar crack growth), we have coupled the <a href="node/597" target="_blank">x-fem</a> to a new fast marching algorithm. Here are couple of animations on growth of an inclined penny crack in tension (unstructured tetrahedral mesh with just over 12K nodes): <a href="http://dilbert.engr.ucdavis.edu/~suku/xfem/GIFS/nonplanar_anime12.gif" target="_blank">larger `time' increment </a>and <a href="http://dilbert.engr.ucdavis.edu/~suku/xfem/GIFS/nonplanar_anime30.gif" target="_blank">smaller `time' increment</a>. This is joint-work with Chopp, Bechet and Moes (NSF-OISE project). I will update this page as and when more relevant links are available. </p>
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</div></div></div>Wed, 04 Apr 2007 21:40:29 +0000N. Sukumar1215 at https://imechanica.orghttps://imechanica.org/node/1215#commentshttps://imechanica.org/crss/node/1215