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Updated: 9 hours 34 min ago

Thanks, for the elucidating

Mon, 2021-10-04 06:28

In reply to Dear Per,

Thanks, for the elucidating comment Yaolu. I agree, it would absolutely be interesting to explore both higher and lower crack growth velocities. 

At fracture mechanical testing of tough nuclear pressure vessel steel performed at Oak Ridge National Lab it was observed that the sudden arrest occurs at a substantial velocity. As you know the mechanics behind it was later explained by Freund and Hutchinson (1985) as a consequence of the strain rate dependent material. 

The steady state solution below the arrest velocity for which lower velocity requires higher load, meaning loss of load control. With that, the obtained solution for that part becomes a demarkation line between immediate arrest or a jump to an inertia controlled much higher crack growth velocity. 

The model is not intended for crack growth at very low velocities below the arrest velocity. The crack tip, modelled as a singular point, causes the required remote load to become unlimited as the crack tip velocity vanishes. If the point shaped crack tip is replaced with the distributed fracture processes that your cohesive zone model provides, the vanishing crack tip velocities and initiation of crack growth might be modelled. Who knows, with a very low cohesive stress perhaps the crack arrest will be wiped out?

Best regards, Per

Thanks Mujibur for making me

Sat, 2021-10-02 10:46

In reply to Discussion of fracture paper #30 - Weight functions, cracks and corners

Thanks Mujibur for making me aware. The page is now open access until december 31st. Due to a change of personel at Elsevier EFM the upgrading of non open access fell between chairs. Best regards, Per

PS Interesting method but why restricted to convex cracks? What are your thoughts? DS.


Hi Lixiang,

Thu, 2021-09-30 10:38

In reply to Hi Katie

Hi Lixiang,


Sure, and thanks for your interest.  I'd be happy to discuss more.  Please feel free to reach out to me.




Hi Katie

Thu, 2021-09-30 09:53

In reply to Journal Club for September 2021: Phononic materials: controlling elastic waves in solids

Hi Katie,

   Thanks for your detail reply. It makes sense to me. Great work. It is very very interesting topic. I need to speed time to read more of your papers. I have some more questions regarding to Phononic materials. I may ask you in the future. 



Dear Per,

Sun, 2021-09-26 09:29

In reply to Discussion of fracture paper #29 - Fast Crack Growth in Fibre Reinforced Composites

Dear Per,

The aspects of crack arrest that you mention are interesting. I am familiar with the work of Freund and Hutchinson that apply to materials with rate dependent dislocation based plasticity. With ample time, the dislocations slide around and give plastic deformation that shields the crack tip region and impede the energy from reaching the crack tip. The reason for the arrest seems to be that the dislocations doesn't respond as expected to rapidly increased load. With amorphous polymer materials it could be different. 

The crack arrest is an interesting phenomenon that I guess for structure could be good but also risky. If the static situation does not allow crack growth is alright but if an impinging stress wave or something whatever kickstarts crack growth and then, even if the stress wave is gone in a blink, continued growth requires less load would not be good.

With the numerical framework proposed in this paper, it is possible to model crack arrest that is expected to occur if an even smaller loading velocity is applied on the SENT specimen. On the other hand, it is observed that the maximum crack speed in the paper is around 270 m/s, it would be interesting to explore higher loading rate region when the crack speed becomes a larger fraction of the Rayleigh wave speed, but of course the convergence behaviour of the implicit dynamic framework becomes a true pain.

Best regards,


Zhenjiang is one of the most

Fri, 2021-09-17 12:33

In reply to Post-doc positions available at Jiangsu University, China

Zhenjiang is one of the most beautiful city in China, near to Yangzi river. A city with lengend story. I like it.

I was in Prof. G.R. Liu's FEA

Fri, 2021-09-17 12:13

In reply to Post-doc positions available at Jiangsu University, China

I was in Prof. G.R. Liu's FEA course 

Only shortlisted candidates will be notified, thanks

Thu, 2021-09-16 04:47

In reply to Post-doc positions available at Jiangsu University, China

Only shortlisted candidates will be notified, thanks


Wed, 2021-09-15 13:55

In reply to Discussion of fracture paper #30 - Weight functions, cracks and corners


Can you please attach the paper? I would appreciate it greatly.


Mujibur Rahman

very interesting

Tue, 2021-09-07 13:30

In reply to Journal Club for August 2021 - Electromechanics of Polyelectrolytes

Meredith, thank you for this nice and short summary on the electromechanics of polyelectrolytes! Very interesting topic. I am surprised that there has been no discussions yet. Will come back with some soon.

Hi Lixiang,

Wed, 2021-09-01 16:24

In reply to Question?

Hi Lixiang,

Thanks for your questions:  

1. If a structure has a complete band gap, neither the longitudinal waves nor the shear wave will propagate in the band gap.  The physics behind the band gap is related to constructive and destructive interference of waves at the interface between different media.  In the band gap, the reflected/transmitted waves at interfaces completely cancel, so there is no energy propagation.  Physically, the energy remains localized within the ~first unit cell.

2. The condition for a shear wave traveling faster than a longitudinal wave relates to the relation of the components of the elastic stiffness tensor, and is typically restricted to certain propagation directions. We achieved this by designing a lattice that has an off-diagonal component that is negative and less than the shear component (in our particular lattice, this was C_13 < -C_44), so one needs an auxetic material to realize such effective properties. The direction of the polarization anomaly depends on the ratio between uniaxial stiffness components.  






Mon, 2021-08-30 23:56

In reply to Journal Club for September 2021: Phononic materials: controlling elastic waves in solids

Hello Dear,

    Thanks for sharing the interesting and nice research work. I am new. Can I ask some questions?

        1) Can longitudual and shear wave propagate through band gap? What is the physics behind it? Localization?

        2) How did you achieved  that shear wave speed is faster than longitudal wave speed ?

Thank you,


I forgot to mention that the

Sun, 2021-08-29 08:34

In reply to 2020-2021 Harvey Price Awardee: Prof. james R. Rice

I forgot to mention that the Harvey Prize is awardedby Technion, Israel Institute of Technology

ABAQUS default stiffness

Fri, 2021-08-27 07:14

In reply to How to select the cohesive material parameters (stiffness, dama

I am wondering if you know the default stiffness value in ABAQUS surface based cohesive behavior? Many thanks!

non-classical continuum mechanics lecture notes

Thu, 2021-08-26 03:24

In reply to Lecture notes of interest to mechanicians

Dear Colleagues,

Are there any lecture notes on non-classical continuum mechanics available?

especially on :

1- continuum mixture mechanics

2- higher-order continuum mechanics

3- higher-grade continuum mechanics 

3-(strongly) non-local continuum mechanics?


kind regards


3D Hashin failure criteria usdfld

Tue, 2021-08-17 08:17

In reply to User defined failure criteria in abaqus

you can find a tutorial and the usdfld subroutine in the following link

Many scientists are on Twitter

Sun, 2021-08-15 08:50

In reply to No twitter account

In many ways, Twitter is a mode of publishing familiar to researchers. You choose to publish what feels right to you. Each tweet is accessible to everyone (with or without Twitter account), has a time stamp, and can be linked by other tweets. Twitter is a great way to meet other reserachers and tell them about your papers.

Here are tips of getting started written by a communication expert: 

No twitter account

Sat, 2021-08-14 16:16

In reply to I have just tweeted about you, Kosta

Dear Zhigang,

Thank you! I dont have a Twitter account or any other account :))  I am a fighter for privacy :))) The last one.

I have just tweeted about you, Kosta

Sat, 2021-08-14 12:29

In reply to PhD in Mechanics of Soft Materials and Biological Tissues

It's an ongoing thread of tweets. I'm no sure where I will go with it yet. Do you have a Twitter account? Twitter is iMechanica on steroid. 


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