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Discussion of fracture paper #25 - The role...

Tue, 2020-01-14 11:28

In reply to Discussion of fracture paper #25 - The role of the fracture process region





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Thank you very much for your interest in our paper and for reading it so thoroughly. I think it’s an interesting discussion and reflection. For instance, the fact that the cohesive zone has two independent parameters, the fracture energy and the maximum stress, does not really turn the model into a two-parameter model in the same sense as the K-T or the J-Q models. These other models represent more of the surrounding mechanical state than the two-parameter cohesive zone model is able to account for.

Nailing the cohesive stress, I believe, is a tricky issue. It seems to me that for ductile materials this entity lacks a clear physical interpretation, and therefore tends to play the role of a fitting parameter. Another issue that you raise is whether the present set of parameters is general enough to predict the behavior of considerably longer cracks or for short or even vanishing cracks. Although we have not investigated the predictive ability of the model for these cases, I would expect that the prediction would be far from perfect. One reason is, as you mentioned, that the cohesive zone is taken to be autonomous, that is independent of what is going on around it.

We have actually performed experiments for growing cracks as well (not published yet). These results have not been fully evaluated, but preliminary results indicate that it is, for instance, difficult to predict the behavior for long crack growth using the present approach. Furthermore, it is evident that during crack growth, the rate dependence of the fracture process is very important to capture accurately.

Finally, the question must also be raised if the cohesive zone concept is really the best way to model this kind of crack growth which exhibits a lot of ductility. In the study, we did some preliminary investigations of the fracture surfaces, but I would say that further examinations of the actual fracture process are needed. Such investigations might suggest if, for example, a continuum damage model is a better approach to model fracture of these materials.

Indeed a great loss for all

Thu, 2020-01-09 11:34

In reply to Professor Emeritus Ali Argon at MIT, pioneer in the mechanics of materials, dies at 89

Indeed a great loss for all of the Solid Mechanics community.

Position filled

Mon, 2020-01-06 08:49

In reply to Postdoc Opening in Computational Materials Science at Rutgers University

This position has been filled. Thank you to all who applied.

Discussion of fracture paper #24 - The sound of crack growth

Sun, 2019-12-29 11:23

In reply to Discussion of fracture paper #24 - The sound of crack growth

Dear Claudia,

Your follow up experiments and simulations are very interesting. When you say that you use cohesive zone models to simulate the fracture processes it strikes me that how smart that must be. I guess that you by that can figure out the length of the crack while the short crack are expected to develop long cohesive zones vis à vis cohesive zones at long cracks. Also the major part of the cohesive zone would host fracture processes that endure high stresses while the fracture processes at crack tips of longer cracks are exposed stresses that are more evenly distributed between zero close to the crack tip and a maximum stress at the tip of the cohesive zone. 

I guess that if the acoustic spectrum of the high stress initial fracture processes and the low stress fracture processes are different you would be inform of many things. Perhaps state of the process region, crack length and length of the process region. At least theoretically.

I don't know what the capabilities are but at least to me it seems like the sky is the limit.

Per Ståhle

PS Sorry about the delay with this reply. DS

position now filled

Sun, 2019-12-29 10:03

In reply to Postdoctoral fellowship in computational fracture mechanics at Duke University

This position is now filled.  Many thanks to those who applied or expressed interest in it.


Fri, 2019-12-27 00:05

In reply to 2019 Timoshenko Medal Acceptance Lecture: J.N. Reddy



again thanks

Thu, 2019-12-26 04:36

In reply to So what are you unknows: u

Look dear Bin

I have a differential equation for wave motion as the PDF file.

then, I can write the weak formulation for this differential equation in two forms again as the PDF files and also according to these two formulations of weak form we have two different boundary conditions too. When I solve these two forms of weak formulation I get two different results. Now, I want to know that, are they the same and my code is wrong or they are different basically and if they are different which one is true?

my phone number on WhatsApp is: +989368021916

It's my pleasure to become your new friend.

Congratulations!  Very well

Wed, 2019-12-25 19:26

In reply to 2020 Journal of Applied Mechanics Award - Shengqiang Cai

Congratulations!  Very well deserved!!

thank you, Xuanhe!

Wed, 2019-12-25 16:29

In reply to Dear Stephan,

thank you, Xuanhe!

Merry Christmas and happy New Year!

So what are you unknows: u

Wed, 2019-12-25 09:14

In reply to Thanks yes I did these two step

So what are you unknows: u and any others?

Thanks yes I did these two step

Wed, 2019-12-25 07:03

In reply to you can times the both sides

Hello dear

Thank you very much for your attention. Yes, I did these two steps and the forms 1 and 2 are after those. The first differential equation after weak formulation can be written in two forms. I want to know that those are different or are the same for getting the results.

you can times the both sides

Tue, 2019-12-24 21:21

In reply to About weak formulation

you can times the both sides with test function, then integrate by part only with the terms have spatial derivative.

Video accessible to all, now

Mon, 2019-12-16 04:42

In reply to A steel sphere impacting and propagating in water


Video not accessable

Sun, 2019-12-15 07:18

In reply to A steel sphere impacting and propagating in water

Hi, Rittel, just a reminder that your video you want to disseminate on Youtube is set as private and thus not accessable to outsiders.

So happy to hear this great news, Shengqiang!

Sat, 2019-12-14 17:57

In reply to 2020 Journal of Applied Mechanics Award - Shengqiang Cai

With deep admiration for your creativity and kindness.

Congratulations Shengqiang

Sat, 2019-12-14 12:35

In reply to 2020 Journal of Applied Mechanics Award - Shengqiang Cai

Richly deserved!

Big congratulations, Shengqiang!

Fri, 2019-12-13 17:02

In reply to 2020 Journal of Applied Mechanics Award - Shengqiang Cai

Big congratulations for the well-deserved award, Shengqiang!

Abaqus mailing list

Thu, 2019-12-12 15:22

In reply to Visualizing deformation gradient via SDV in Abaqus VUMAT



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Many Congratulations

Thu, 2019-12-12 10:39

In reply to 2020 Thomas J.R. Hughes Young Investigator Award - Professor Xuanhe Zhao

Well-deserved recognition! Congratulations, Xuanhe!! 

Big congratulations for the well-deserved award!

Wed, 2019-12-11 18:44

In reply to 2020 Thomas J.R. Hughes Young Investigator Award - Professor Xuanhe Zhao

Dear Xuanhe,

Big congratulations for the well-deserved award!


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