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i am using XFEM in a 2D analysis (plate under uniaxial tension) and would like to get the SIFs at different crack lengths to compare with published data for verification before i start performing crack propogation analyses.


My problem is, history outputs are not available for crack growth in XFEM only static cracks (at least from what i read).  

Ideally, i would love to get the SIFs as they change through the crack propagation. 


Anyone have any ideas on this? 

Thanks in advance.

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any feedback?

Abaqus does not provide SIF output for moving crack.  Formulation of solution does not permit and/or they have not implemented to have provide SIF as you suggest.  I have had that discussion with Abaqus support and experts for quite some time.  Apparently, this has not been considered to be a priority to them. 

 One way to approach the problem is to put in a specific request to have this implemented.

Another way, there may be some industrial code or personal code that someone has developed that can take output from Abaqus anlaysis and calculate the SIF solution for you.  I understand that a company has done just that, and that they claim that Abaqus does not properly post process the information to obtain SIF accurately.  I can vouch for some issues with SIF solutions even for stationary crack analysis.  Abaqus indicated that they would address issues, and claimed that some already were addressed at the time of my request, to make various improvements for release in version 6.12.  That I am told did not happen, even those improvements that were apparently already implemented.

Abaqus also provided me (you may find on their support website I understand) a python script (plugin actually) to help extract SIF for stationary cracks, rather than the tedious method of manually extracting.  It failed to work for me, even after two different versions were sent to me by Abaqus support.

You might consider the following.  Depending upon what type of analysis you are conducting, you may be able to use the crack growth rate information to get a fair estimate of the SIF solution.  It may be more complex than that to extract from Abaqus output, but the concept itself is feasible.

Another approach is to utilize the output from Abaqus as the crack is growing, and use the crack geometry as input to a static XFEM analysis.  Again, conceptually doable, the scripting required to implement may or may not be worth your effort.

If you find an alternative solution to your needs, I would be interested in what you find.  I had a similar interest/need.  I have not made the investment to implement any of my suggestions above.

Good luck.


Frank Richter's picture

Hello mcgrete,

I hope you look into this thread once more.

Did you note that I replied on your ancient posting
Stress Distributions in Helical Compression Springs

Unfortunately, you do not disclose your e-mail adress to iMechanica users; I thus use this thread here to let you know.


Frank Richter



 I just now downloaded and used the Abaqus PlugIn that I referenced.

I realize that it does not help you with your dynamic crack growth issue, but if you reach a state where you use the static crack, it is a little helpful to plot SIF.  I did not use the option to output data to Excel, but one exists with it.  I did find that the tool does not have a clear means of specifying which frame/step/increment for which the results are being plotted (or saved perhaps).  I found that it did not consistently use the step/increment of interest, even when I last plotted a contour plot (say Mises stress) for that given increment.  Proceed with caution; no apparent instructions on which step/increment could be located.


The data does exist in the *.dat file.  As such, I think that it might be useful to write a python script (or other language of your preference) to extract and manipulate the results to your needs.




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