FEA on a chassis Help!

[mnmhalstead]

Hi All,
Before I start I would like to say that I a novice in FEA and would like to learn as much as possible through this forum.
So hence any useful comments would be much appreciated.
I would like to run a Static analysis on a chassis and this is what I propose to do.
I would like someone to validate my thoughts or point me in the right direction.

Scope of the analysis is to find out if the chassis is strong enough to withstand the following loads and highlight weak areas.
Yield Stress of the material is : 450 Mpa
3D Tetrahedral mesh used.
Surface to surface contact between chassis members.

A Force of 34335 N is applied to the lower Deck and is distributed across all the beams that come in contact with the floor.
I propose to use Fix constraints on four RHS points that connect to the suspension system.
A force of 4905 N in applied on the Kingpin that connects to the upper Deck.

After solving I get this error in F06 file.
"SYSTEM FATAL MESSAGE 3000 (CNTITER2)
ITERATIVE SOLUTION FAILED DUE TO FAILURE OF PRECONDITIONER TO FACTOR.
THIS ERROR CAN RESULT IF THE STRUCTURE IS NOT RESTRAINED SUFFICIENTLY TO PREVENT
RIGID BODY MOTION OR IF INTERNAL MECHANISMS EXIST."
How do I add more constraints to achieve my goals?

See pic attached.

Thanks
Regards
Mike

 

[BlasMolero]

hello!,
This error is typical for beginners in FEM/FEA, means that your model is not properly constrained and you have rigid body motions. A trick is to perform a modal eigenvalue analysis (SOL103) and animate the deformed shape of modes whose frequency is zero (o near to zero as 1e-4), this will tell you the parts that are not properly constrained or free to move as rigid body, OK?. Take a look to the following post:

http://iberisa.wordpress.com/2011/0...run-terminated-due-to-excessive-pivot-ratios/

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[mnmhalstead]

Hi BlasMolero,
Thanks a lot for the tip. I shall try your method.