Case Study – Thermal Expansion for RBE2/RBE3s

Posted byScott LeePosted inUncategorized

A common misconception I have seen throughout my career is erroneous modeling of RBE2s and RBE3s whenever performing a thermal analysis.

Aerospace structures consist of both metallic and composite materials. Due to the CTE differences between the two, thermal mismatch is prevalent across the joints (i.e. whenever you have an aluminum structure interfacing with a composite structure). Therefore, additional joint loads will be developed whenever you run your thermal loading in Nastran SOL101.

There are instances where you may be modeling your joints with a combination of RBE3 – CBUSH – RBE3. Therefore, it is important to model the RBE3s appropriately when performing any type of thermal analysis.

In addition, there may be cases where you have a multitude of RBE2s within your model. It is very important to model the RBE2s correctly for whenever performing a thermal analysis, as the results may be highly erroneous if not modeled accurately.

To model RBEs appropriately, you must perform two actions:

  1. Specify a CTE value within all of your RBE2s and RBE3s within your model
  2. Turn RIGID = LAGRAN on within your nastran deck (i.e. in FEMAP, turn on the toggle Rigid Element Thermal Expansion)

For further details on this topic, please see the links below.

RBE2_RBE3_Rigid_LagrangeDownload

Published by Scott Lee

Hello. I have been in the aerospace stress industry for 13+ years. I have a passion for building FEM models and I am continuously looking for ways to improve the FEA processes and flows. Being able to "move faster" will give companies a competitive edge within the development process of an aircraft, as well as in other arenas. In addition, it is highly important to be able to build your models as accurately as possible. This site will go over the decision making processes and explain why one technique of modeling may have been chosen over another technique.

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