Semi Eliptical Crack fracture Ansys

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  • Last Post 14 September 2018
josejjpc posted this 08 September 2018

I am doing the same estudy and when the results it is solved I receive a error mensager "A fracture result is specified by time instead of by set. If the time lies between two result sets, no interpolation is performed. Instead, there are two possibilities: (1) if there are no mesh changes, the lower set applies; (2) if there are mesh changes, the closest set applies" 

I receive the value 1157,2Mpa.mm^(0,5), but in my calculation should be close to 1608,92 according Abaqus or 1726,55 according API standard.

someone could help me?

semi eliptical external crack dimension (longitudinal direction):
63,2mm major radius 
15,8mm minor radius
pipe external radius: 1158,8mm
pipe internal radius: 1139,8mm
pipe lenght: 800mm
Internal pressure: 3.5Mpa

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SandeepMedikonda posted this 09 September 2018

Hi Josejjpc,

  I am not an expert in crack/fracture, but here are some answers from my colleague who is:

The first question seems to be answered by the error message: 

"A fracture result is specified by time instead of by set. If the time lies between two result sets, no interpolation is performed. Instead, there are two possibilities: (1) if there are no mesh changes, the lower set applies; (2) if there are mesh changes, the closest set applies" 

It appears that he is requesting the fracture results at a time that is not associated with a results set.  He has chosen an intermediate time.  We can interpolate stresses for intermediate times, but we cannot interpolate fracture results.  To obtain a valid fracture result, he needs to specify a results set or specify a time that correlates with a results set.

I do not believe that we can provide a generic answer for the second question: 

"I receive the value 1157,2Mpa.mm^(0,5), but in my calculation should be close to 1608,92 according Abaqus or 1726,55 according API standard. "

There could be many causes:

  • poor mesh,
  • insufficient number of contours,
  • using results from the first several contours,
  • contours outside the FE domain, etc.

Regards,

Sandeep

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josejjpc posted this 10 September 2018

Hi Sandeep, I worked in the fracture file and I changed set instead time for result and now it is without error, but the result do not change.

About causes that you mentioned, do you know how to improve mesh to solve this problem?

I know that Ansys has the capability to do semi-eliptical crack and solver correctily, but in examples that have in youtube or internet do not has the same problem that I have.

thanks for your help util now.

SandeepMedikonda posted this 10 September 2018

Josejjpc,

  There is one example in the Cornell Learning Modules

  Additionally, you can find numerous examples to learn from in the ANSYS Verification Manuals (about 24). Can you please check those out?

  Hope this helps.

Regards,
Sandeep

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josejjpc posted this 10 September 2018

 Sandeep, thanks for your attention, examples mentionded in ANSYS Verification Manuals have similar as my problems, but I don't know how to do in ansys.

 

this examples is so close my:

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v191/wb_vm/wbvt_VMSIM041.html

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v191/wb_vm/wbvt_VMSIM082.html 

But I don't know how to create in Ansys, I just know how to do semi eliptical crack, and in this manual does not teach how to do. That is my problem, how to refine mesh and configure to get the right results.

SandeepMedikonda posted this 10 September 2018

Hi josejjpc,

Can you please refer to this and the subsequent posts for tutorials on meshing. There are numerous other discussions on the forum about meshing as well.

P.S: I had to remove the links to Sharcnet, so I replaced them with the links from the document which are more upto date.

Regards,

Sandeep

SandeepMedikonda posted this 10 September 2018

Also, there are 2 specific examples on Crack which can provide some insight into meshing here.

josejjpc posted this 14 September 2018

Hello Sandeep, thanks for help me with this links, I did the example: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v191/mech_tut/ds_fracture_stresspt.html

In this example the result is 26599MPa.mm(^0.5), but the result the I am getting is 25599MPa.mm(^0.5). It is showing the same message:

"A fracture result is specified by time instead of by set. If the time lies between two result sets, no interpolation is performed. Instead, there are two possibilities: (1) if there are no mesh changes, the lower set applies; (2) if there are mesh changes, the closest set applies" 

Do you think that this is normal message or the variation in final results is because computer processor?

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