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Simulating Roll stiffness leaf spring

Question asked by Tim Van Lunteren on Apr 30, 2014
Latest reply on May 1, 2014 by Tim Van Lunteren

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Hello,

First let me introduce myself. I'm Tim and I am graduating for automotive engineer in Holland.

For my thesis I need to simulate different worst case scenario's for transverse leaf springs.

Almost everything is doing great in solidworks 2013 simulation, but I encounter a problem when simulating roll stiffness.

I want to know what different end and centre sections of the leaf spring will influence the stiffnesses.

The leaf spring is 1200mm long.

So in the real world the transverse leaf spring will be clamped in rubbers at 1/3th and 2/3th of the length.

On the left end of the leaf spring acts 3500 N upwards in the vertical direction, and on the right side 3500 N downwards.

So, the leaf spring should form like an 'S' shape. But, it doesn't do it. It can calculate, but the solution does not make sense at all...

I've been trying without fixtures (so only an equilibrium), and i've been trying with spring fixtures.

Both give the same stupid answer.

I don't know how to proceed from here to get the right simulation.

Can someone help me or send me into the right direction?

See the Attachment (warning, it is an educational version!!)

With kind regards,

Tim

Aaron Gradeen Apr 30, 2014 9:25 AM

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Hey Tim,

Can you upload a picture of the results which you are saying don't make sense? I'm assuming those are bolt holes which secure the leaf. Why not use those as a rigid fixture? If you take the sum of your moments about the left side of the leaf, equillibrium is not satisfied. I also noticed one of the forces you apply to the bolt hole is per item and the other applied force is total. Are you getting any warnings when you run the simulation?

-Aaron

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Leaf spring calculations Roll stiffness.zip59.9 KB

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Aaron Gradeen Apr 30, 2014 9:25 AM

Hey Tim,

-Aaron

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Tim Van Lunteren @ Aaron Gradeen on Apr 30, 2014 9:36 AM

Hey Aaron,

I think you are right about the equilibrium, and that is in my opinion also the case why it does not work. I don't use a rigid fixture, because in the real world it will be clamped with rubber bushings, which will not function as a rigid fixture!

how do you think i should move on?

Tim

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Aaron Gradeen @ Tim Van Lunteren on Apr 30, 2014 9:49 AM

Hey Tim,

I understand. Modeling the rubber bushings as a rigid fixture would give you higher forces in the leaf and would therefore be conservative. Is using a non rigid fixture not working out either? On the other hand, if you want to turn this into a thesis, you could use solidworks simulation to account for the damping and the stiffness in those rubber mounts. I'm guessing this would also bring in viscoelastic effects of the rubber. This would not be a simple simulation to run. You would have to know how those 3500 N forces are applied over time.

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Jared Conway @ Aaron Gradeen on Apr 30, 2014 10:12 AM

I think first pass with split lines for the rubber bushings and fixed restraints is the way to go.

Then you can add complexity like the rubber bushings. As long as the displacements stay low you can stay in linear.

Did you happen to use soft springs or inertial relief? Or get a large displacement error? That could cause the issues you are describing.

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Tim Van Lunteren @ Aaron Gradeen on May 1, 2014 3:17 AM

I have set the equilibrium of moments from the left side of the leaf spring.

That was the whole mistake. Simulation is working it out just fine now.

Also, my manual calculation wasn't right before, but it is set up properly now.

Thnx!

Tim

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5 Replies

Aaron Gradeen Apr 30, 2014 9:25 AM
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Hey Tim,
Can you upload a picture of the results which you are saying don't make sense? I'm assuming those are bolt holes which secure the leaf. Why not use those as a rigid fixture? If you take the sum of your moments about the left side of the leaf, equillibrium is not satisfied. I also noticed one of the forces you apply to the bolt hole is per item and the other applied force is total. Are you getting any warnings when you run the simulation?
-Aaron
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- Tim Van Lunteren @ Aaron Gradeen on Apr 30, 2014 9:36 AM
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  Hey Aaron,
  
  I think you are right about the equilibrium, and that is in my opinion also the case why it does not work. I don't use a rigid fixture, because in the real world it will be clamped with rubber bushings, which will not function as a rigid fixture!
  
  how do you think i should move on?
  
  Tim
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  - Aaron Gradeen @ Tim Van Lunteren on Apr 30, 2014 9:49 AM
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    Hey Tim,
    I understand. Modeling the rubber bushings as a rigid fixture would give you higher forces in the leaf and would therefore be conservative. Is using a non rigid fixture not working out either? On the other hand, if you want to turn this into a thesis, you could use solidworks simulation to account for the damping and the stiffness in those rubber mounts. I'm guessing this would also bring in viscoelastic effects of the rubber. This would not be a simple simulation to run. You would have to know how those 3500 N forces are applied over time.
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    - Jared Conway @ Aaron Gradeen on Apr 30, 2014 10:12 AM
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      I think first pass with split lines for the rubber bushings and fixed restraints is the way to go.
      
      Then you can add complexity like the rubber bushings. As long as the displacements stay low you can stay in linear.
      
      Did you happen to use soft springs or inertial relief? Or get a large displacement error? That could cause the issues you are describing.
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- Tim Van Lunteren @ Aaron Gradeen on May 1, 2014 3:17 AM
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  Correct Answer
  I have set the equilibrium of moments from the left side of the leaf spring.
  That was the whole mistake. Simulation is working it out just fine now.
  Also, my manual calculation wasn't right before, but it is set up properly now.
  
  Thnx!
  
  Tim
  Like • Show 1 Like1
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Simulating Roll stiffness leaf spring

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