Showing results for 
Search instead for 
Do you mean 
Solved! Go to solution

Beam element with non-linear material properties



I am simulating a model which includes preloaded bolts. Beam elements have been used with a preload force to represent this. Solver used is advanced non-linear static.


The analysis run gives an error in the very beginning if I use an elastic-plastic material model for the beams. I searched for this issue on the forum here and it seems I cannot use a non-linear material. But to have a realistic simulation I need to include yielding in the bolts.


Could anyone help me with this?





Re: Beam element with non-linear material properties

For beam elements in advanced nonlinear(sol 601), you must use the bilinear, plasticity modulus input. In addition to this requirement, you must use the PBEAML for the property. This is not stated explicity in the QRG under PBEAM, but it is noted under PBAR.


2. PBAR cannot be used for elasto-plastic beam elements.  For elasto-plastic
beam elements, PBARL with circular (TYPE = –ROD– or •TUBE–) or
rectangular (TYPE=–BAR–) cross sections must be used.


The NASTRAN documentation is being updated to make this clear for the PBEAM in addition to PBAR. 


In Femap, this means you must the "NASTRAN" section when creating your property, and you are limited bar,tube, or rod as sections.

2017-05-08 10_16_08-Femap with NX Nastran - [beamtest.modfem] - [Untitled].png





Re: Beam element with non-linear material properties

Hello, thanks for your answer. I tried to run the model after incorporating your comments. I am getting an error again. Please see the attached images for information about bolt cross-section, material model and the error message.




Accepted by topic author SG3
‎05-11-2017 05:12 PM

Re: Beam element with non-linear material properties

This is a limitation for advanced nonlinear solutions, bolts defined using beam elements must use a linear elastic material model. 

You have 2 options that I can think of:

 1) solid elements can be defined as a bolt, there is no limitation on material model using solid elements as a bolt. From the advanced nonlinear guide: A set of 3-D solid elements can be combined into a bolt (called
a 3D-bolt). The elements can use any formulation (small or large displacements, small or large strains), any material model and any number of nodes per element.

2) use multiple beam elements for the bolt, let a single element with linear elastic material be defined as the bolt, the other elements would not be included as bolt elements and could use the nonlinear material model. You would need to run a test model and confirm that this concept behaves as you desire for your particular model.


Re: Beam element with non-linear material properties

[ Edited ]

hello, thanks for your response!

I will go for option 1.