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Updated: 12 hours 10 min ago

Try modifying B.C.

Thu, 2015-07-30 08:35

In reply to tension and torsion in ABAQUS

You should be modifying (and not deactivating in this case) the boundary condition from the first step when you move to the second.

Thank you for organizing the meeting

Wed, 2015-07-29 13:57

In reply to 1st Midwest Mechanics of Materials and Structures workshop at UIUC campus on Aug. 26th 2015

Yuhang,  thank you and Ahmed for initiating the midwest mechanics workshop, it reminds me the great fun and success of the New England Workshop on Mechanics of Materials and Structures. I look forward to attending its first event and its series years after!

Thank you so much

Wed, 2015-07-29 13:43

In reply to Thanks for writing in detail.

Thank you so much

it  worked :)


abaqus modeling of steel tubular x-joints under tensile loading

Wed, 2015-07-29 08:17

In reply to ABAQUS Tutorial and Assignment #1

Hi all,

I have some problems in verification of my model. Can anybody help me?

Thank you Mr Singh, but my

Wed, 2015-07-29 03:44

In reply to "For brittle material it is

Thank you Mr Singh, but my question is about ductile materials and the damage critirion available in abaqus for this kind of material to choose with the XFEM methode, any sugestions?

EMU Peridynamic code

Wed, 2015-07-29 02:57

In reply to Peridynamic theory vs. classical continuum theory

Can anyone send me EMU code of peridynamic?

The link does not work. any help will be greatly appreciated 

"For brittle material it is

Tue, 2015-07-28 12:00

In reply to Ductile crack modeling with XFEM and Damage criterion in Abaqus

"For brittle material it is possible to use the XFEM methode coupled with the Maximum Principal Stress criterion": Yes, it is possible. When you give the material properties in Abaqus you can choose this criterion under "Damage initiation".

exponential softening cohesive zone (ABAQUS)

Tue, 2015-07-28 09:54

In reply to exponential softening cohesive zone (ABAQUS)

I mean the curve is not given for energy-based damage evolution.



Mon, 2015-07-27 00:34

In reply to Could you tell me know which criteria if satisfied, the abaqus give this error "one of your elements distorted excessively"?

Dear Dincoz

I'm working on multiscale modeling of soft tissues. In my case the deformation are moderately small but sometimes distortion error is occured. With regard to my experience, this error show that the solution process is diverged and it may be because material instability or unstability at contact elements. You should check your material model parameters or solver parameters like timestep size.

Reply to teng

Sun, 2015-07-26 05:26

In reply to When iMechanica meets WeChat......

Exllent points. I write this iMechanica comment within wechat. See if it works. 

When iMechanica meets WeChat......

Sat, 2015-07-25 22:16

In reply to Friends of Extreme Mechanics Letters

I was at a conference in Hong Kong when the Wechat group of "Friends of EML" was established by Zhigang. Many attendants of the conference are already indeed friends of iMechanica, so it took minimum efforts to get many of them in this new Wechat group. Before the conference was over, I noticed the number of group members went from 2-digit to 3-digit. You start to see people inviting other friends in their circles to join the group. This reminds me the early days of iMechanica: after some initial publicizing efforts, the registrated users of iMechanica just increase by word of mouth.

The advent of smartphone is changing many facets of our life everyday. Mobile messaging communication service such as Wechat and Whatsapp makes connecting and communicating with each other radically easier and in ways that are nearly impossible in past. I was first amazed by the power of Wechat about two years ago, when a friend of mine snapped a photo with a monk at a tea stand in Tibet and shared in our Wechat group in real time. Then a few group members online started to converse, including him in Tibet, one in Japan, some in Beijing and Shanghai, and some in US, me included. While such a conversation was technically possible even before Wechat was launched, it often involved the use of a computer and took some time to set up. So not many people bother to set up to discuss a random snapshot while traveling. Now with smartphone and apps like Wechat, such communications and sharing become so easy that even my folks can do so. I feel much more closer and connected with family and friends, and I'm sure many find the same.

The ease to use aside, Wechat cannot serve all we need at iMechanica. Conversations in a Wechat group go in a single thread, so one can easily get lost in an active discussion. Time stamp exists but is transient. It is challenging to retrieve historical communications. By contrast, iMechanica allows multi-thread discussions, with permanent time stamp and archiving of all conversations, which are searchable as well. Many of us have enjoyed the in-depth discussions over iMechanica and our monthly Journal Club has been a signature feature of iMechanica for exactly the same reasons. On the other hand, iMechanica is not ideal either.  For example, posting an image or a figure in a post or a comment is not trivial. I've answered tons of questions, such as how to post images, from many iMechanica users and still find the solutions we can offer awkward to apply.

So for us, Wechat will not replace iMechanica, but we need both. Per Wikipedia, as of August 2014, WeChat has 438 million active users; with 70 million outside of China. I assume these numbers still increase. Per BaiduBaike, Chinese version of Wikipedia, by first quarter of 2015, wechat has 549 million users from 200 countries in 20 languages, it's installed in 90% smartphones in China. Just like computers, smartphones will be everywhere, only at a much faster sweeping pace. Let's just embrace all possible ways to get connected with each others and wait to see how wechat can do for mechanicians and mechanics. 


—posting from a high speed train at 180 miles/hour in China (I took a snapshot of the speed display but find not easy to post the image here…. :-)

Cool idea!

Sat, 2015-07-25 21:24

In reply to Friends of Extreme Mechanics Letters

Dear Zhigang, it's very cool to have a such a tool for mechnics people to communicate directly!

Zhigang, this is a good idea.

Sat, 2015-07-25 18:56

In reply to Friends of Extreme Mechanics Letters

Zhigang, this is a good idea...I too, until perhaps very recently, did not use my cell phone beyond its classical features. I started using Whatsapp (---which is similar to Wechat) in order to stay in touch with some of my friends from high school and now many others around the world including my relatives in India.

Discussion of mechanics will be an unusual application of Wechat! But, in a short while, may feel as natural as it now feels to use iMechanica on our laptops.

Are there recommendated books/lecture notes about fatigue mechan

Sat, 2015-07-25 12:14

In reply to Are there recommendated books/lecture notes about fatigue mechan

Are there recommendated books/lecture notes about fatigue mechanics, and damage mechanics, wear and corrosion available?  Oli Mobil Terbaik di Indonesia – Total Quartz


Re: updated notes on entropy

Sat, 2015-07-25 11:06

In reply to updated notes on entropy

I added a very short section on the quantum mechanics of hydrogen atom.  This way can can talk about quantum states of isolated system using a concrete example.

Thanks for writing in detail.

Fri, 2015-07-24 22:13

In reply to vertex and node in abaqus

Thanks for writing in detail.

I don't think there should be a conflict if you are calling nodes based on node labels. I just tried calling a node at a location where a vertex also exists. I used...

mdb.models[modelname].rootAssembly.instances[instancename].nodes[nodelabel] for the node, and

mdb.models[modelname].rootAssembly.instances[instancename].vertices[vertexlabel] for the vertex

and ABAQUS reports the corresponding entity correctly. The only difference being that the node labels are always zero indexed, i.e. if you are looking for node label 20, you should call 19 and so on. This is not needed for vertices, just call 20 as 20.

I hope this helps, or you could share your code here for further examination.


Thanks for your reply.

Fri, 2015-07-24 12:50

In reply to vertex and node in abaqus

Thanks for your reply.

The problem is that, for example node 4, a node in my model  :

      1,           0.,           0.,           2.
      2,  0.800000012,           0.,           2.
      3,           0., -0.800000012,           2.
      4,           0.,           0.,           4.
      5,  0.800000012,           0.,           4.
      6,           0., -0.800000012,           4.
      7,  0.800000012,           0.,           0.
      8,           0.,  0.800000012,           2.
      9,           0.,  0.800000012,           0.

as you can see, node 4 has coordinates of  0.,           0.,           4.

but also in the model, there is a vertex number 3, has the same coordinates!! which means that there is a vertex on the node 4.

Now I am writing a script which depends on the node numbers. But when I call the node 4, it becomes another one, because this node with these coordinates are already taken by the vertex!!!

Is there a command by which I can delete or hide the vertices when I call the nodes?!!



Could you please write in

Fri, 2015-07-24 10:39

In reply to vertex and node in abaqus

Could you please write in more detail as to what exactly is the issue ?

Did not get what you meant by "The vertices changes the nodes numbers when I call the nodes!!!!"

For a more complete discusion

Thu, 2015-07-23 17:32

In reply to I answer just be definition

For a more complete discusion, you might also want to include (from the same dictionary) the definition of positive or reverse discrimination: the act of giving advantage to those groups in society that are often treated unfairly, usually because of their race, sex, or sexuality.

Hi Zheng,

Thu, 2015-07-23 13:52

In reply to Dear Shu,

Hi Zheng,

You are correct that unit rotation will cause severe stress concentration in the joints. In real materials, especially those less-stretchable materials, it will break the joints and thus the structure is less expandable, which is one of the limitaiton of cuts. With Shu, we have a paper under review discussing the mechannical and phononic behavior of the hierarhically cut metamaterials made of brittle and superelastic materials. In the paper, we do see the joints break in the first level joints in both materials. We have proposed two strategies to address the issue you mention. One is through design of the local cut shape and the other is design of global distribution of hinge width across hierarhical levles to distibute the load more evenly to each level. Hope I have answered your quesiton. Thanks.



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