iMechanica - fracture mechanics - Comments

Reza Avazmohammadi Thanks

Reza Avazmohammadi — Wed, 17 Sep 2008 09:04:15 -0400

Reza Avazmohammadi

Thanks Dear Andri for your comments and your referencesAs I have realized, you mean that the configurational force is pertinent to an material inhomogeneity (or defect) embedded in a continuum space, undergoing remote loading. For the case of an inhomogeneity (inclusion) we can easily compute this force by integrationg the computed stress around the inhomogeneity, but it seems there is a general method for driving this force for general inhomogeneitise and defects, isn't it?I want to know what the adjective "configurational" wants to show? and what is the application of obtaining this force?Thanks again.Reza

Configurational force

Andri Andriyana — Tue, 16 Sep 2008 14:16:43 -0400

Dear Reza,

Unlike what we know as physical forces (push-pull forces, generated
by displacement in the physical space), the configurational forces (or
material forces) are generated by displacement in a so-called material
manifold (material space, an abstracts set of particles that constitute
the body). As an example of this kind of force is the one that acts on
a point of singularity, on a dislocation line (Peach-Koehler force), on an inhomogeneity, ....
For more insight, I would recommend you the papers of G. A. Maugin,
particularly:

G. A. Maugin, (1995). Material Forces: Concepts and Applications.
Appl. Mech. Rev. 48, 213-245.

If I'm not misinterpreting your question, then the configurational
equilibrium should be the pull-back of the classical equilibrium
equations into the material manifold. In other words, expressing the
equilibrium equations in the purely material description. Again you'll
find a lot of info on this matter in the above paper.

Andri

Books worth reading on this subject:

G. A. Maugin, (1993). Material Inhomogeneity in Elasticity. Chapman
and Hall, London.

R. Kienzler and G. Herrmann, (2000). Mechanics in Material Space.
Springer, Berlin.

M. E. Gurtin, (2000). Configurational Forces as Basic Concept of
Continuum Physics. Springer, Berlin.

excellent

Farid Touaiti — Fri, 29 Aug 2008 06:12:24 -0400

thank you very much.

Blogging with LaTeX!!

HY Shadow Huang — Thu, 21 Aug 2008 17:20:09 -0400

Hi Alex,

Thanks for this info. Finally I am able to type math entries in the blogs. I've tried it out and it worked perfectly.

Thanks again!!

force-displacement curve vs traction-separation curve

Zhigang Suo — Thu, 21 Aug 2008 13:46:35 -0400

Dear Samuel: Thank you for your comments. Other users have also reported difficulties with posting comments on iMechanica. The difficulties seem to be restricted to users with Internet Explorer as their browser. This problem with posting comments can be fixed. I have also put this link on the right side of iMechanica, under Quick Guide.

Now let me turn to your question about the mechanics of bridged cracks. Force-displacement curve is what you measure when you apply a mechanical force to your specimen. The two faces of the crack separate, but part of the crack may be bridged. Many models assume a relation between the separation of the crack and the traction in the bridge.

In a typical model, the separation-traction relation is given as an input, and one can calculate the force-displacement curve. In an experiment, of course, you measure the force-displacement curve, and try to infer the separation-traction relation.

These basic ideas are reviewed by G. Bao and Z. Suo, Remarks on crack-bridging concepts," Applied Mechanics Review45, 355-366 (1992). Many other people have worked on the subject, too. Let's hope someone can direct you to papers more specific to your experiment.

Traction-separation law

Sergej Tarasov — Sun, 27 Jul 2008 08:07:22 -0400

From my experience, the shape of traction-separation curve has little effect on the load-displacement curve for linear materials. The initial stiffness of the cohesive elements should affect the slope of the first part of load-displacement curve, and the "sharpness" of the peak load value depends on the strength (maximal traction) of the elements. As the crack propagates all curves should practically coincide, as we see in Case 3. But results for Case 1 look quite strange.

Excellent work

yanyabin — Sat, 26 Jul 2008 10:00:23 -0400

You have done an excellent work!

Here what I want to say is that I am also working on using cohesive elements to simulate the delamination process in pizeoelectric thin films. Layers in this kind of thin films are in micrometer or even nanometer scale. What's more, my simulation is also based on a sandwiched-cantilever experiment.

In my simulation, some different kinds of cohesive zone models are used and their traction-separation laws are programmed in the user subroutine in ABAQUS. By reading your paper attached in your blog, I know that the bilinear cohesive zone model was used in your simulation. So, did you applly other kinds of cohesive zone models in your simulation? Did you code their constitutive relations in the user subroutine?

Therefore, I am very interested in communicating with you about the cohesive zone models. Do you have spare time to have this kind of communication with me?

PS: My e-mail: yanyabin@gmail.com.

regards

yanyabin