iMechanica - cohesive element
https://www.imechanica.org/taxonomy/term/879
enABAQUS files of coupled Mullins effect and cohesive zone model for fracture and adhesion of soft tough materials
https://www.imechanica.org/node/22162
<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/3950">soft materials</a></div><div class="field-item odd"><a href="/taxonomy/term/31">fracture</a></div><div class="field-item even"><a href="/taxonomy/term/27">adhesion</a></div><div class="field-item odd"><a href="/taxonomy/term/879">cohesive element</a></div><div class="field-item even"><a href="/taxonomy/term/3552">mullins effect</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"> </p>
<p class="MsoNormal"><a name="OLE_LINK21" id="OLE_LINK21"></a><a name="OLE_LINK20" id="OLE_LINK20"></a><a name="OLE_LINK19" id="OLE_LINK19"></a><a name="OLE_LINK18" id="OLE_LINK18"></a><a name="OLE_LINK17" id="OLE_LINK17"></a><span><span><span><span><span>Soft materials including elastomers and gels are pervasive in biological systems and technological applications. Robust mechanical properties, such as high toughness and tough bonding, are crucial to realize the potentials of soft materials. It has been well recognized that building energy dissipation into an elastic network is </span><span>one important toughening mechanism</span><span>. </span><span>However, it is still challenging to </span></span></span></span></span><a name="OLE_LINK16" id="OLE_LINK16"></a><a name="OLE_LINK15" id="OLE_LINK15"></a><span><span><span><span><span><span><span>quantitatively</span></span></span></span></span></span></span><span><span><span><span><span><span> predict the synergistic effect of the intrinsic fracture energy and mechanical dissipation </span><span>in process zone due to the highly nonlinear deformations. We recently showed that a coupled Mullins effect and cohesive zone model can accurately predict the fracture toughness and adhesion of tough hydrogels. The coupled simulation model can be carried out with finite element software ABAQUS. With the new experimental techniques, material fabrication and numerical methods, it is very promising to rationally design novel soft tough materials and quantitatively predict the designed materials with simulations. To further promote research on fracture and adhesion of soft tough materials, we share the ABAUQS input files for simulating fracture and 90 degree peeling of tough hydrogels. Please change the files to ".inp" after you download them to run the simulations with ABAQUS. </span></span></span></span></span></span></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal"><span>Zhang, Teng, Shaoting Lin, Hyunwoo Yuk, and Xuanhe Zhao. "Predicting fracture energies and crack-tip fields of soft tough materials." </span><em>Extreme Mechanics Letters</em><span> 4 (2015): 1-8.</span></p>
<p class="MsoNormal"><span>Yuk, Hyunwoo, Teng Zhang, Shaoting Lin, German Alberto Parada, and Xuanhe Zhao. "Tough bonding of hydrogels to diverse non-porous surfaces." </span><em>Nature materials</em><span> 15, no. 2 (2016): 190.</span></p>
<p class="MsoNormal"><span>Zhang, Teng, Hyunwoo Yuk, Shaoting Lin, German A. Parada, and Xuanhe Zhao. "Tough and tunable adhesion of hydrogels: experiments and models." </span><em>Acta Mechanica Sinica</em><span> 33, no. 3 (2017): 543-554.</span></p>
</div></div></div><div class="field field-name-upload field-type-file field-label-hidden"><div class="field-items"><div class="field-item even"><table class="sticky-enabled">
<thead><tr><th>Attachment</th><th>Size</th> </tr></thead>
<tbody>
<tr class="odd"><td><span class="file"><img class="file-icon" alt="Plain text icon" title="text/plain" src="/modules/file/icons/text-plain.png" /> <a href="https://www.imechanica.org/files/gel_h20_ogden1_s080md100_k2000_v125.txt" type="text/plain; length=2547299">gel_h20_ogden1_s080md100_k2000_v125.txt</a></span></td><td>2.43 MB</td> </tr>
<tr class="even"><td><span class="file"><img class="file-icon" alt="Plain text icon" title="text/plain" src="/modules/file/icons/text-plain.png" /> <a href="https://www.imechanica.org/files/gel_h20_ogden1_s080md100_k2000_v0625.txt" type="text/plain; length=2547301">gel_h20_ogden1_s080md100_k2000_v0625.txt</a></span></td><td>2.43 MB</td> </tr>
<tr class="odd"><td><span class="file"><img class="file-icon" alt="Plain text icon" title="text/plain" src="/modules/file/icons/text-plain.png" /> <a href="https://www.imechanica.org/files/gel_peeling_2d_ogden2_s200d30_h32.txt" type="text/plain; length=734933">gel_peeling_2d_ogden2_s200d30_h32.txt</a></span></td><td>717.71 KB</td> </tr>
<tr class="even"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://www.imechanica.org/files/User%20guides_0.pdf" type="application/pdf; length=443349">User guides.pdf</a></span></td><td>432.96 KB</td> </tr>
</tbody>
</table>
</div></div></div>Fri, 23 Feb 2018 04:40:15 +0000Teng zhang22162 at https://www.imechanica.orghttps://www.imechanica.org/node/22162#commentshttps://www.imechanica.org/crss/node/22162Cohesive Analysis with Abaqus/Explicit
https://www.imechanica.org/node/15826
<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/324">delamination</a></div><div class="field-item odd"><a href="/taxonomy/term/879">cohesive element</a></div><div class="field-item even"><a href="/taxonomy/term/3740">Abaqus/Explicit</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 all,</p>
<p>
I'm trying to model composite delamination under non-severe impact on layered composites in ABAQUS/Explicit.
</p>
<p>
To begin with, I've modeled a 2D aluminum with a finite very low thickness cohesive layer with traction-separation behavior between. Then, I give some displacement to the middle-top node to simulate an impact scenario. However, even in this simple configuration, I'm having stress distribution problems when the models with cohesive layer between and without cohesive layer are compared.
</p>
<p>
The problem is, I'm having some ridiculous stress distribution and meaningless bubbles when I model with cohesive elements, at the beginning of the step. I'm also having different stress outputs for the cases with and without cohesive layer.
</p>
<p>
I noticed that the stress output result varies with:
</p>
<p>
Cohesive layer in-plane thickness<br />
Cohesive layer density<br />
Cohesive layer penalty stiffness (Knn, Kss, Ktt)
</p>
<p>
From what I've read from literature, the common belief is using default thickness, very low density and very high penalty stiffness for those fields. However, with any try with those values, I couldn't get meaningful results.
</p>
<p>
Here's my input file for the cohesive & non-cohesive cases and the pictures of the problem I'm experiencing: <a href="https://www.dropbox.com/sh/igpidoms47xdvf4/MGHg3Gi">https://www.dropbox.com/sh/igpidoms47xdvf4/MGHg3Gi</a>...
</p>
<p>
Thanks in advance.
</p>
</div></div></div>Fri, 20 Dec 2013 09:14:33 +0000madmaxx15826 at https://www.imechanica.orghttps://www.imechanica.org/node/15826#commentshttps://www.imechanica.org/crss/node/15826Crack Propagation by Cohesive Element
https://www.imechanica.org/node/15792
<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 everyone,
</p>
<p>
I've been working on crack propagation problem by cohesive elements in Abaqus.
</p>
<p>
I have a sandwich struture where adhesive bonds two steels together. And I've attached part of my input file in the following.
</p>
<p>
I can have the stress and strain distribution, but I really expect the crack will propagate in the midplane of the adhesives. I don't know whether I have to preset a line in the middle of adhesive as existing crac, or I can set some crack interaction to get the crack growth result.
</p>
<p>
I've stuck in this problem for several days, and tried to found out online. However, I've met several similar problems but no solutions provided. I really appreciate that some idea or advice could be given.
</p>
<p>
Thanks a lot,
</p>
<p>
I set the adhesive property is *Material, name=Mat_Adhe<br />
*Damage Initiation, criterion=QUADS<br />
3.3e+06, 7e+06, 7e+06<br />
*Damage Evolution, type=ENERGY, mixed mode behavior=POWER LAW, power=1.<br />
330.,800.,800.<br />
*Damage Stabilization<br />
0.001<br />
*Elastic, type=TRACTION<br />
8.5e+08, 8.5e+08, 8.5e+08
</p>
<p>
The step is *Step, name=Step-1, nlgeom=YES, inc=10000<br />
*Static<br />
0.005, 1., 1e-09, 0.01
</p>
<p>
And the field output is *Node Output<br />
CF, PHILSM, RF, U<br />
*Element Output, directions=YES<br />
LE, PE, PEEQ, PEMAG, S, STATUSXFEM
</p>
<p>
history output is *Node Output, nset=Total-1.Set-1<br />
RF1, RF2, RF3, RM1, RM2, RM3, U1, U2<br />
U3, UR1, UR2, UR3<br />
</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/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/694">crack propagation</a></div><div class="field-item odd"><a href="/taxonomy/term/879">cohesive element</a></div></div></div>Sat, 14 Dec 2013 00:52:41 +0000bowen.raymone15792 at https://www.imechanica.orghttps://www.imechanica.org/node/15792#commentshttps://www.imechanica.org/crss/node/15792Cohesive Zone and Cohesive Element
https://www.imechanica.org/node/14845
<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>
I had been trying to reproduce a crack propagation problem using XFEM/Cohesive Zone. The problem is a 200x200x50 notched plate which has been simulated using plane strain elements 200x200 with 50 mm thickness.
</p>
<p>
I generated the cohesive layer (zero thickness) between the plane strain elements in the notch region, as cohesive elements and cohesive material properties which will define the crack initiation location.
</p>
<p>
Is there any other method of doing the same using cohesive zone? In other words, Is the use of 'Cohesive Elements' and 'Cohesive Zone Method' one and the same?
</p>
<p>
I would be grateful if anyone could kindly enlighten.
</p>
<p>
</p>
<p>
Best Regards,<br />
Baburaj
</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/694">crack propagation</a></div><div class="field-item odd"><a href="/taxonomy/term/879">cohesive element</a></div><div class="field-item even"><a href="/taxonomy/term/5449">cohesive zone</a></div></div></div>Sun, 16 Jun 2013 03:46:40 +0000baburaj14845 at https://www.imechanica.orghttps://www.imechanica.org/node/14845#commentshttps://www.imechanica.org/crss/node/14845Abaqus cohesive elements/cohesive surface
https://www.imechanica.org/node/14142
<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>For my<br />
graduation project I’m working on a model to describe cracking behavior. For<br />
this model I want to model a fibre-epoxy interface, see the attached figure 1<br />
(due to symmetry only a quarter is modeled). The fibre part is modeled with<br />
lineair elastic material. The epoxy part is modeled with CPS4 elements, with<br />
elastic behavior and MAXPS damage (damaged evolution included). The connection<br />
between the fibre and epoxy interface can be modeled with both a cohesive<br />
surface and cohesive elements. However<br />
cohesive surface will give inaccurate results due to peak stresses (see<br />
attached image 2). </span>
</p>
<p class="MsoNormal">
<span> </span>
</p>
<p class="MsoNormal">
<img src="http://i47.tinypic.com/ibdmph.jpg" alt=" " width="292" height="254" /></p>
<p class="MsoNormal">
<span> </span>
</p>
<p class="MsoNormal">
<img src="http://i47.tinypic.com/158bdc3.jpg" alt=" " width="794" height="550" /></p>
<p class="MsoNormal">
<span> </span>
</p>
<p class="MsoNormal">
<span>For the<br />
attached image 2 I tested single cohesive elements, and two lineair elastic<br />
elements (very high E-module, thus these approach infinite stiffnes) connected<br />
with a cohesive surface. </span>
</p>
<p class="MsoNormal">
<span> </span>
</p>
<p class="MsoNormal">
<span>Therefor I<br />
want to model the fibre-epoxy interface with cohesive elements instead of<br />
cohesive surfaces. I previously used a cohesive surface to model the<br />
interaction (before I found out about the inaccurate results). The cracking in<br />
the epoxy interface was modeled with XFEM. The results of the model where<br />
reasonable, however not completely correct. The normalized traction separation<br />
diagram is added in figure 3. However this normalized traction separation<br />
diagram should look as attached figure 4 as found by Alfaro and Suiker (2010). </span>
</p>
<p class="MsoNormal">
<span> </span>
</p>
<p class="MsoNormal">
<span>Alfaro, M.<br />
Suiker, A. (2010) Transverse Failure Behavior of Fibre-epoxy systems, Journal<br />
of Composite Materials, Vol. 44, No. 12/2010.</span>
</p>
<p class="MsoNormal">
<span> </span>
</p>
<p class="MsoNormal">
<img src="http://i49.tinypic.com/2cpcc5w.jpg" alt=" " width="889" height="516" /></p>
<p class="MsoNormal">
<span> </span>
</p>
<p class="MsoNormal">
<img src="http://i49.tinypic.com/rmjuyv.jpg" alt=" " width="696" height="562" /></p>
<p class="MsoNormal">
<span> </span>
</p>
<p class="MsoNormal">
<span>So I tried<br />
to adjust the model, and change the fibre-epoxy interface from a cohesive<br />
surface to cohesive elements. When these cohesive elements are modeled the<br />
behavior of the model is however completely incorrect.</span>
</p>
<p class="MsoNormal">
<span> </span>
</p>
<p class="MsoNormal">
<span>The input<br />
(.inp) files for both the cohesive surface and the cohesive element fibre-epoxy<br />
interaction can be found here:</span>
</p>
<p class="MsoNormal">
<a href="https://dl.dropbox.com/u/21539688/Cohesive%20element.inp">Cohesive element.inp</a>
</p>
<p class="MsoNormal">
<a href="https://dl.dropbox.com/u/21539688/cohesive%20surface.inp">Cohesive surface.inp </a>
</p>
<p class="MsoNormal">
<span> </span>
</p>
<p class="MsoNormal">
<span>Why does<br />
Abaqus give completely different answers to the model when cohesive elements<br />
are used to model a fibre-epoxy interface.</span>
</p>
<p class="MsoNormal">
<span>And how can<br />
the model be adjusted to behave correctly. </span>
</p>
<p class="MsoNormal">
<span> </span>
</p>
<p class="MsoNormal">
<span>Thank you<br />
in advance,</span>
</p>
<p class="MsoNormal">
<span>Any help<br />
would be very helpful!</span>
</p>
<p class="MsoNormal">
<span> </span>
</p>
<p class="MsoNormal">
<span>Steven</span>
</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-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/128">education</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/418">xfem</a></div><div class="field-item odd"><a href="/taxonomy/term/879">cohesive element</a></div><div class="field-item even"><a href="/taxonomy/term/1350">cohesive</a></div><div class="field-item odd"><a href="/taxonomy/term/8422">cohesive surface</a></div></div></div>Tue, 05 Feb 2013 16:47:16 +0000StevenS14142 at https://www.imechanica.orghttps://www.imechanica.org/node/14142#commentshttps://www.imechanica.org/crss/node/14142Journal Club Theme of August 2012: Mesh-Dependence in Cohesive Element Modeling
https://www.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://www.imechanica.orghttps://www.imechanica.org/node/12899#commentshttps://www.imechanica.org/crss/node/12899how to define cohesive element property? because the cohesive element layer is our imaginary
https://www.imechanica.org/node/12784
<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/87">crack</a></div><div class="field-item odd"><a href="/taxonomy/term/879">cohesive element</a></div><div class="field-item even"><a href="/taxonomy/term/7719">fracturing</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>I'm modeling rock fracture problem with cohesive element. I konw the propertiey of the solid element around the fracture because we can measure it (rock sample) in the lab. but as regard to how to define the propeties of cohesive element, I'm completely lost. </p>
<p>in fact, the cohseive element is a fictitious one, not a real matearial in the physical world, we can't mearsure its propety by physical means. then how can we know what parameters we should enter ?</p>
<p>need your help, thanks</p>
</div></div></div>Mon, 16 Jul 2012 04:02:35 +0000hanrrycn12784 at https://www.imechanica.orghttps://www.imechanica.org/node/12784#commentshttps://www.imechanica.org/crss/node/12784how can I link vumat to cohesive elemet
https://www.imechanica.org/node/8003
<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/879">cohesive element</a></div><div class="field-item odd"><a href="/taxonomy/term/1588">VUMAT</a></div><div class="field-item even"><a href="/taxonomy/term/5046">stressold</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,
</p>
<p>
recently,i want to write a delamination law using vumat,but coh3d8 element with a traction-separation has s33,s13,s23.in vumat,stressold(nblock,ndir+nshr),i don't kown if s33 is correspond to stressold(nblock,3),and if s23 is correspond to stressold(nblock,5),
</p>
<p>
i hope someone can help me.
</p>
</div></div></div>Fri, 16 Apr 2010 06:47:12 +0000wangyun8003 at https://www.imechanica.orghttps://www.imechanica.org/node/8003#commentshttps://www.imechanica.org/crss/node/8003Using cohesive elements in Abaqus
https://www.imechanica.org/node/6575
<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/879">cohesive element</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>
I have used Traction Sepration law for modelling a crack by using pore pressure cohesive elements-I have observed both damage initiation and damage evolution law and I checked by QUADSCRT output that my damage initiation criteria has been satisfied I also have used<strong> PFOPEN</strong> output(Pore fracture opening at integration outputs) observed that my fracture opening increased from 2 mm to around 8 mm during a 2o min step time that means that crack initiates and propogates but I dont see any crack forming in my model when I see the model in Abaqus Viewer -Does anybody have experience what's wrong with the model ?Is crack really happens? why pfopen shows that the pore fracture changes but I dont see any crack forming in my model output. I have copied and the paste the inp lines:
</p>
<p>
*COHESIVE SECTION,ELSET=cohesive,MATERIAL=cohesive,RESPONSE=TRACTION SEPARATION,<br />
THICKNESS=SPECIFIED, CONTROLS=VISCO_upper<br />
0.002<br />
*SECTION CONTROLS,NAME=VISCO_upper,VISCOSITY=0.01
</p>
<p>
*MATERIAL, NAME=cohesive<br />
*ELASTIC,TYPE=TRACTION<br />
50E9,50E9,50E9<br />
*DAMAGE INITIATION,CRITERION=QUADS<br />
1e5,1e5, 1e5<br />
*DAMAGE EVOLUTION,TYPE=ENERGY, SOFTENING=LINEAR, MIXED MODE BEHAVIOR=BK,POWER=2.284<br />
117,117,117<br />
*GAP FLOW<br />
1.e-3<br />
*FLUID LEAKOFF<br />
5.879E-11,5.879E-11
</p>
<p>
I can also share the full inp file if somebody can help.
</p>
<p>
</p>
<p>
</p>
<p>
</p>
</div></div></div>Sun, 02 Aug 2009 21:48:58 +0000Diana W.Smith6575 at https://www.imechanica.orghttps://www.imechanica.org/node/6575#commentshttps://www.imechanica.org/crss/node/6575How to define the contact state if the corresponding cohesive element is under compression (ABAQUS)
https://www.imechanica.org/node/6346
<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/289">ABAQUS</a></div><div class="field-item odd"><a href="/taxonomy/term/356">friction</a></div><div class="field-item even"><a href="/taxonomy/term/555">compression</a></div><div class="field-item odd"><a href="/taxonomy/term/879">cohesive element</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. I am currently using cohesive element traction-separation law for modeling interface element between FRP and concrete. Can any one tell me how to define the contact state if the corresponding cohesive element is under compression in ABAQUS? Yes, it's said that there won't be any damage if pure compression is applied to cohesive element, but my questions is how to consist of assuming that friction occurs on the damaged part as there is no friction definition in cohesive traction-separation law. Please add comments if you know something about this. Thanks for help ^_^
</p>
</div></div></div>Tue, 21 Jul 2009 12:35:15 +0000xiaoqin6346 at https://www.imechanica.orghttps://www.imechanica.org/node/6346#commentshttps://www.imechanica.org/crss/node/6346Using cohesive elements to model delamination in a lap shear experiment
https://www.imechanica.org/node/6054
<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/324">delamination</a></div><div class="field-item odd"><a href="/taxonomy/term/879">cohesive element</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>
I have conducted single lap shear tests on aluminium laminates, bonded with a polypropylene film adhesive, and am now trying to model the experiments. I am using cohesive elements, with a bi-linear traction separation law to model the adhesive layer. I can obtain reasonable agreement for the peak force, using the nominal shear stress obtained by experiment as the stress at which the cohesive element begins to soften. However, the initial slope of the computation force-displacement curve is approximately double that of the experiment. I am using a penalty stiffness of the order of 1e12 N/m^3 which is already low in comparison to most K values quoted in the literature. I have tried stiffness values 2-3 orders of magnitude lower, which does not change the F-d slope at all. If I drop K even lower, the computation becomes unstable. This is all fairly consistent with what I have seen in the literature about cohesive elements.
</p>
<p>
My question is whether anyone is familiar with published research on modelling of "pure shear" with cohesive elements? I know that a lap shear specimen is not "pure shear" but it is definitely more Mode I than Mode II. All of the literature I have come across so far focusses on test geometries where the slope of the global force displacement curve is governed by something other than the cohesive element (e.g. in a double cantilever beam experiment the bending stiffness of the cantilevers drives the initial force-displacement response) - in most of the published experiments the displacements are at least on the millimeter scale and in most cases final displacements are in 10s of mm. In my experiments peak load occurs at at a displacement of 0.15mm(after correcting for test frame compliance).
</p>
<p>
</p>
</div></div></div><div class="field field-name-upload field-type-file field-label-hidden"><div class="field-items"><div class="field-item even"><table class="sticky-enabled">
<thead><tr><th>Attachment</th><th>Size</th> </tr></thead>
<tbody>
<tr class="odd"><td><span class="file"><img class="file-icon" alt="Image icon" title="image/png" src="/modules/file/icons/image-x-generic.png" /> <a href="https://www.imechanica.org/files/LapShear_force_displacement.png" type="image/png; length=71530" title="LapShear_force_displacement.png">LapShear_force_displacement.png</a></span></td><td>69.85 KB</td> </tr>
</tbody>
</table>
</div></div></div>Wed, 15 Jul 2009 15:36:30 +0000Reuben Govender6054 at https://www.imechanica.orghttps://www.imechanica.org/node/6054#commentshttps://www.imechanica.org/crss/node/6054Differences between cohesive/interface/embedded process zone
https://www.imechanica.org/node/2773
<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/128">education</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/879">cohesive element</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>I am PhD student and i'm working on the behavior of bonded joints under impact and i have one question :What are the differences between a cohesive element, an interface element and a embedded process zone element ? Do they have fundamental differences or it's only a difference of the cohesive law expression.</p>
</div></div></div>Thu, 28 Feb 2008 14:30:17 +0000David MORIN2773 at https://www.imechanica.orghttps://www.imechanica.org/node/2773#commentshttps://www.imechanica.org/crss/node/2773Loading problems in simulate crack propagation with cohesive element
https://www.imechanica.org/node/1280
<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/128">education</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/879">cohesive element</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>Hi all:</span></p>
<p class="MsoNormal"><span>When I simulate a crack propagate along interface between film and substrate with cohesive element, different load-deflection curves of film were achieved when I applied load or displacement on film, respectively.<span> </span>I think it should achieve same results regardless which kind of load I selected. <span> </span>Please help me find what’s wrong with my simulation.</span></p>
<p class="MsoNormal"><span>Thanks!</span></p>
</div></div></div>Sun, 22 Apr 2007 03:55:32 +0000Pulin Nie1280 at https://www.imechanica.orghttps://www.imechanica.org/node/1280#commentshttps://www.imechanica.org/crss/node/1280