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MatsLindqvist1-Visitor
1-Visitor
May 30, 2012
Question

Large deformations for shells & beams ?

  • May 30, 2012
  • 1 reply
  • 2197 views

Does anyone, ptc-employees or other, have any idea if/when large deformation analyses will be available for models containing shell and/or beam elements?

Strucures subject to large deformations are often thin-walled, elongetad structures where beam and shell elements would be appropriate.

I often use beams to model assemblies, to model pre-loaded bolts, torque free pivots & joints etc. and it would be very useful if these could be used in large deformation analyses. In statically indeterminate designs with contacts, it's important to combine large deformation theory, with contact, even though deformations appear small. However, it's not possible to do this on a model containing beams.

/Mats Lindqvist/Product specialist - simulation tools/


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1 reply

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ckatsis1-Visitor
1-Visitor
June 1, 2012

We have no specific plans to support large diplacement analyses for beam and shell elements in the near future.

We have thought of allowing the participation of small displacement beams and shells in LDA. It will be up to the user to make sure that all beams and shells are in areas of the model that don't undergo large displacements. We can possibly warn when we detect large displacements in that neighborhood. Do you think this would be useful functionality?

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MatsLindqvist1-VisitorAuthor
1-Visitor
June 4, 2012

Yes it would. In statically indeterminate designs, displacements, even if they are "small", affect how reaction forces are distributed. If a contact analysis is used for such a design, large deformations need to be used, even if displacements are small, since contact is a deformation dependent phenomenon.

statically_indeterminate.jpg

I often use this picture in training. In a statically indeterminate constraint case, as shown left above, the distribution of reaction forces are affected by the stiffness of the surrounding environment, as indicated in the right picture. An engineer, presented with a design proposal as in the left figure, should ask the question of what is the stiffness of the surrounding structure, and include that either as springs with realistic stiffness and/or by including the actual components in the analysis. However, if contacts are used in such a case, large deformation analysis should be used, even if deformations are "small", or else the distribution of reaction forces will be incorrect. Being able to use beams in combination with LDA would help modeling more complex structures that are statically indeterminate and have contacts.

Another question I receive a lot, is wether it's possible to create measures on beam endpoints for beam section quantities, such as shear&moment. Once again, in a statically indeterminate design, if the surrounding environment, connections etc. is modeled using beams, it's useful to be able to create measures for shear&moment forces. I see now that it's possible for springs, but not for beams.

/Mats L

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