iMechanica - failure - Comments

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Pengfei Liu — Tue, 27 Dec 2011 00:43:29 -0500

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Now, multiaxial failure criteria of composites is an important direction not only for fatigue loads but also various loads since conventional failure criteria cannot hold for these special load environments.Howverer,experiments for multiaixal loading is also a large challenge.

ask

Honggang Jia — Thu, 15 Dec 2011 23:15:18 -0500

if you call for article about crack growth in composite structure

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Honggang Jia — Thu, 15 Dec 2011 21:01:27 -0500

my email:z770428@sina.cn
tele:15191903657
I am from China
my major is failure mechanic

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Honggang Jia — Thu, 15 Dec 2011 20:58:44 -0500

my email:z770428@sina.cn
tele:15191903657
I am from China
my major is failure mechanic

http://mypage.zju.edu.cn/per

Pengfei Liu — Tue, 08 Feb 2011 20:04:14 -0500

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Prof. Stephan Rudykh:

It is a novel research work in area of fiber composites.I What to know what the stability analysis results will be if viscous(or elasto)-plastic properties of matrix is considered? Thank you!

Pengfei Liu

Re: Reliability

Biswajit Banerjee — Tue, 01 Feb 2011 19:53:42 -0500

A recent paper related to our work is

"Error bounds for the reliability index in finite element reliability analysis" by L. Gallimard in IJNME.

DOI: 10.1002/nme.313

-- Biswajit

Wish it helpful to you

Jin MZ — Fri, 26 Feb 2010 04:58:38 -0500

If you want to model the a porous material plate with avialable constitutive model. I think the HELP document in ABAQUS is enough.

If you want to build the microstructure model and study its unknown mechanical properties, I think everyone is begin from the book： Cellular Solids by Gibson and Ashby.

Chen C., Lu T. J., Fleck N.A., 1999. Effect of imperfections on the yielding of two dimensional foams, J. Mech. Phys. Solids 47 2235-2272 is also recommended.

Study 5 minutes at least every day

Hi Hao, write

Angela Maria Piccolo — Thu, 25 Feb 2010 08:23:55 -0500

Hi Hao,

write poroelasticity in the search bar of imechanica (top right corner). Then have a look at Suo's blog: "poroelasticity and diffusion in elastic solids". Here you can find some papers. For example "Foundamentals of poroelasticity", which is really very good.

Angela

re: question

Konstantin Volokh — Tue, 15 Dec 2009 17:05:55 -0500

Dear Azadeh,

There are two possible answers:

1. The experiments have to be done more carefully. ( I like this answer)

2. The theoretical calibration should be done for the whole range of the biaxial data while it was done for the uniaxial failure only.

And, finally, I do not think that the experimental data is THAT different from the theory .

Sincerely,

Kosta

Question

Azadeh Sheidaei — Tue, 15 Dec 2009 11:59:01 -0500

Dear Prof Volokh,

I have some questions regarding your paper”

On modeling failure of rubber-like materials”

Figure 6 shows critical failure stretches based on hyperelasticity with energy limiters and experiment. As you have mentioned in the paper you have varied n (biaxiality ratio) to create different load conditions so each of the points on this plot corresponds to different biaxiality ratio. My question is why experimental data distribution is different compare to theoretical data. Thanks

Azadeh

I think the energy criteria

dhruba — Sat, 24 Oct 2009 00:28:20 -0400

I think the energy criteria is much more reliable in plastic stage,since the energy(area under stress-strain curve) continues to increase in plastic stage. Where as stress doesn't.

re

Konstantin Volokh — Wed, 02 Sep 2009 04:28:50 -0400

Dear Shailendra,

Good to hear from you . I do not know the physics behind the phenomenon you describe. However, my feeling is that you probably need the damage description of the sort that they use for a description of the Mullins effect in rubber. Your problem looks more like a problem of the material evolution rather than the complete bond rupture where energy limiters could be good.

-Kosta

Nice concepts

Shailendra — Wed, 02 Sep 2009 03:34:03 -0400

Dear Kosta,

I read your JMPS papers recently and found the idea of energy limiters very interesting and conceptually appealing. One of the problems we are looking at in our research group is the description of damage or so-called plasticization in polymers due to diluent ingress. I am trying to figure out if we could cast the problem of elastic softening (one aspect of plasticization, the other being the glass transition temperature) into the framework that you describe. The core idea would be to identify right physics for the softening function within the context of the problem. We are still cranking our way through the chemical and physical changes to a polymer (e.g. epoxy) that manifest in modulus degradation.

It would be great to discuss the problem with you to pick your brain on this.

Thanks,

~Shailendra

A review of cohesive-zone models

Zhigang Suo — Sun, 01 Feb 2009 08:22:00 -0500

There is a large body of work on cohesive laws. Here is a review I wrote a while ago:

G. Bao and Z. Suo, "Remarks on crack-bridging concepts," Applied Mechanics Review. 45, 355-366 (1992).

This review should give you a basic idea of cohesive-zone models.

About traction-sepation laws

vinh phu nguyen — Sat, 31 Jan 2009 12:33:54 -0500

Hi Ruchika,

I am also interested in traction-separation laws (TSLs). I do not know much but there are something that I can tell you.

Basically, a TSL expresses the relation between the traction and the displacement jump on the crack surfaces. There are mode I STLs and mixed mode STLs. In the former, only the normal traction and the normal displacement jump delta u_n matter. Whereas, in the latter both normal and tangential are involved.

There are rigid STLs and non-rigid STLs. For rigid STLs, the traction starts from the tensile strength of the material while for non-ridig STLs there is a linear elastic stiffness. Often, the former is employed in XFEM where the crack is introduced whenever a failure criterion is met. The latter is used in finite elements with interface elements since you need the linear elastic stiffness to model the perfect bond before fracturing.

About numerical methods used for STLs, there are XFEM where cracks can be located arbitrarily on the mesh, or interface elements (also called cohesive zone elements) where cracks are along the interboundaries of the elements (hence it limits the application of the method). There is also the embeded strong discontinuity method where the enhanced strain method is used to represent the displacement discontinuity inside the element.

By the way, I do not well know how to do the stress update for STLs. I mean how to handle loading, unloading, penetration (negative displacement jump) ... If you know how to do, please show me since my current implementation is not robust for STLs for brittle materials although they are just simple laws like linear STL or exponential STL for mode I problems.

Regards,

Phu