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Hexahedral vs Tetrahedral in contact analysis
 
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ravi.bhattar
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Joined: 19 Jun 2015
Posts: 5

PostPosted: Sat Jun 20, 2015 8:16 am  Reply with quote

Dear all
I am a new user to ANSYS workbench. I am trying to do a bending with static torsion analysis on polygonal shaft hub connection on varying fit connections. The result from hex lower and higher order gives almost the same result and converge in acceptable range. But the tetrahedral higher order (with and without inflation) gives too much higher value with maximum von Mises stress being 1.5 times bigger in some cases. I do not find much literature why tetrahedral is giving me so different results. I am unable to decide which result to accept. Please suggest what should I do.
Thank you

Ravi Bhatta
Student
Mechanical Engineering
Grand Valley State University
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benjamin.franklin
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Joined: 20 Sep 2013
Posts: 119

PostPosted: Sun Jun 21, 2015 8:28 pm  Reply with quote

The number of rows of elements along through thickness of the component is one factor to get good result. It is good to have four rows of elements along thickness. Did your model have this?

Regards,
Benjamin Franklin,
Ashok Leyland,
India.

-----Original Message-----
From: Xansys [mailto:xansys-bounces@xansys.org] On Behalf Of ravi.bhattar
Sent: Saturday, June 20, 2015 8:46 PM
To: xansys@xansys.org
Subject: [Xansys] Hexahedral vs Tetrahedral in contact analysis

Dear all
I am a new user to ANSYS workbench. I am trying to do a bending with static torsion analysis on polygonal shaft hub connection on varying fit connections. The result from hex lower and higher order gives almost the same result and converge in acceptable range. But the tetrahedral higher order (with and without inflation) gives too much higher value with maximum von Mises stress being 1.5 times bigger in some cases. I do not find much literature why tetrahedral is giving me so different results. I am unable to decide which result to accept. Please suggest what should I do.
Thank you

Ravi Bhatta
Student
Mechanical Engineering
Grand Valley State University






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ravi.bhattar
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Joined: 19 Jun 2015
Posts: 5

PostPosted: Sun Jun 21, 2015 8:39 pm  Reply with quote

Thank you Benjamin for the reply. The overall width of the component has a numerous rows and the inflation layer has 5 rows. But I used inflation only in the tetrahedral mesh and I have checked the skewness to be below 0.95 in all cases.
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Ravi Bhatta
Student in Mechanical Engineering
Grand Valley State University
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benjamin.franklin
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Joined: 20 Sep 2013
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PostPosted: Sun Jun 21, 2015 8:58 pm  Reply with quote

Is WB showing Tet10 as elements in "Mesh Metrics"? Why because, If we set "Dropped" (by mistake) for element mid-node option in "Details" of Mesh settings, the created elements will be in first order (Tet4). Pls check.

If this is not the case, then there may be some other reason which you need to explore.

Regards,
Benjamin Franklin,
Ashok Leyland,
India.


-----Original Message-----
From: Xansys [mailto:xansys-bounces@xansys.org] On Behalf Of ravi.bhattar
Sent: Monday, June 22, 2015 9:09 AM
To: xansys@xansys.org
Subject: Re: [Xansys] Hexahedral vs Tetrahedral in contact analysis

Thank you Benjamin for the reply. The overall width of the component has a numerous rows and the inflation layer has 5 rows. But I used inflation only in the tetrahedral mesh and I have checked the skewness to be below 0.95 in all cases.

------------------------
Ravi Bhatta
Student in Mechanical Engineering
Grand Valley State University






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| Send administrative requests to xansys-mod@tynecomp.co.uk |
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The information contained in this communication is privileged, confidential and proprietary, and is intended for the sole use of/by the addressee. Usage by anyone other than the addressee is misuse and infringement to Proprietorship of Ashok Leyland Ltd. If you are not the intended recipient, you are hereby notified that any dissemination, distribution or copying of this email or any action or omission taken by you in reliance on it, is strictly prohibited and may be unlawful. If you have received this email in error, please contact the sender by reply e-mail and destroy all copies of the original message.
+-------------------------------------------------------------+
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| Hosted by PADT - www.padtinc.com |
| Send administrative requests to xansys-mod@tynecomp.co.uk |
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ravi.bhattar
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Joined: 19 Jun 2015
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PostPosted: Sun Jun 21, 2015 10:42 pm  Reply with quote

Hi Benjamin
I checked it and it shows Tet10. Since, I used inflation, there are a lot of Wedge 15 as well in the contact region. I used inflation to refine the contact area. Does this setting look reasonable to you ?
Thank you
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Ravi Bhatta
Student in Mechanical Engineering
Grand Valley State University
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eric.nickel
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Joined: 28 May 2015
Posts: 2

PostPosted: Mon Jun 22, 2015 6:16 am  Reply with quote

I'm not sure why using wedge15 elements would cause a problem. Perhaps someone else can speak to that.

Regarding meshing for non-linear contacts, I often use a sphere of influence or face sizing to refine mesh near contacts. If you're using face sizing and want to avoid high aspect ratio elements, you can change the global advanced size function to "On:fixed", and then you can control the growth rate for your face sizing control without changing the global growth rate. You could try this instead of using inflation to see if that helps.

Also, including a screenshot of your mesh as well as the Element Quality histogram might be useful for those trying to help you.
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Eric Nickel
Macdon Industries
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ravi.bhattar
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Joined: 19 Jun 2015
Posts: 5

PostPosted: Mon Jun 22, 2015 1:21 pm  Reply with quote

Dear Eric
I will try to do again without inflation. But, I did previously without changing the global size function changed and got higher results than hexahedrons. I have attached some pictures of the mesh and the mesh metrics if that could point out the trouble area.
Thank you for the suggestions.
[img]: http://postimg.org/image/pbu56m2wd/
[/img]: http://postimg.org/image/a243kjg2f/
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Ravi Bhatta
Student in Mechanical Engineering
Grand Valley State University
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patrick.tibbits
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Joined: 27 Apr 2009
Posts: 38

PostPosted: Tue Jun 23, 2015 10:28 am  Reply with quote

Do the stresses which concern you occur within the contact region? Do they arise primarily from the normal pressure between two bodies in contact?

If not, do the stresses arise from the bending and shear, and occur away from the contact region?

Patrick Tibbits
Cobham
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ravi.bhattar
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Joined: 19 Jun 2015
Posts: 5

PostPosted: Tue Jun 23, 2015 11:52 am  Reply with quote

Dear Patrick
Yes, my maximum stress occurs at the edge of the contact region and the maximum contact stress is dominant and elsewhere the shear stress is dominant.
Thank you
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Ravi Bhatta
Student in Mechanical Engineering
Grand Valley State University
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