iMechanica - bilinear
https://www.imechanica.org/taxonomy/term/7393
enBilinear-Law of cohesive element in LS-DYNA
https://www.imechanica.org/node/12303
<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/1350">cohesive</a></div><div class="field-item odd"><a href="/taxonomy/term/3412">Dyna</a></div><div class="field-item even"><a href="/taxonomy/term/7393">bilinear</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>
Hello,
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I'm coding a user materils for cohesive elemnt in dyna, But I met some problems, hope anyone could give some guidance or help .
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I'm trying to code my own user material subroutine for cohesive element in ls-dyna. The cohesive element formulation is already predefined and exists in *SECTION card ( elform=19).
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By default, four integration points are used for one cohesive element , so my first question is that (1)how do we change number of integration points for one cohesive element ? Because this is not what we can decide in the subroutine part. And I couldn't find any option in any card which would do.
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So with 4 points integration, i tried some basic tests on one cohesive element . For example , I fixed the 4 nodes of the lower surface and then I applied traction and / ou shear displacement on the upper surface nodes. Here comes the problem. When the displacements applied to upper surface nodes are uniform, the output displacement vs. traction/shear force corresponds well to the expected bilinear law. HOWEVER, when the applied displacements are not uniform ( say 2mm/ms at two adjacent node 1,4 and 1mm/ms at node 2,3 ), the displacement saved for the element is by default the one interpolated on the first integration point ( -0.577,-0.577), which means i'll get a 1.7887mm/ms. But apparently, a average displacement of 1mm/ms and 2mm/ms should be more reasonable. Meanwhile, I did the same tests with Mat 138 Cohesive mixed mode by using all same parameters, I get the same result, which is, the constitutive law of a cohesive element is reflected on the first integration point (-0.577, -0.577) instead of the point in the middle of plane.
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So sum up a little bit I raise my second question (2) Have anyone came accros the same problem ? and how do we cope with it ?
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Thanks in advance for anyone's help !
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if anyone is intersted in this subject , I would like to have more discussion on it .
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<a href="mailto:daniel.cheng.chen@gmail.com">daniel.cheng.chen@gmail.com</a>
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CHENG
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</div></div></div>Tue, 17 Apr 2012 00:07:57 +0000salutsun12303 at https://www.imechanica.orghttps://www.imechanica.org/node/12303#commentshttps://www.imechanica.org/crss/node/12303