Leaf Spring Builder - Composite Spring

Unfortunately the leaf springs are modeled as isotropic beams. If you an get an estimate of the overall Youngs Modulus, Elastic Strain, Density, and Damping Ratio of the composite material, that can be used as your material input.

Hope this helps!

Christopher Fadanelli

Of course @EduardoMRech!

That is a potential option. I’m picturing the composite leaf spring to look something like this:

If that’s the case, I think it might be easier to build the leaf spring system manually without using the leaf spring builder, since it would just require a few joints to connect to the axle and clamps for the eyes. If you will be noticing large deflections in the overall system, I would be cautious with the flexbody converging. You could have leaf made up of multiple segments of flexbodies (more like how the leaf springs are made with the builder).

Now, flexbodies are a reduced-order model of a finite element model, which is also purely linear elastic. So, if your main goal is to study yielding or plasticity in the leaf spring, here's what you could do:

With the linear flexbody included in the MotionView model, run a MotionSolve simulation and export the loads (using Load Export). Then, import those loads into an OptiStruct analysis with the full FEA model of the leaf spring. From there, you can run an analysis to study fatigue, plasticity, etc.

Best,

Christopher Fadanelli

Yes linearity can pose an issue with the hysteresis. Typically I suggest to use the midline of the curve. There are a couple of options (will involve a lot of iterative work):

Convert the hysteretic area of the leaf spring into an equivalent viscous damping coefficient. There are some papers that show how to do it. Then include this damping in a dummy spring damper entity between the axle and chassis, most likely a torsional one at the leaf ends. This approach will likely result in a more robust model that solves quickly, but needs some math calculations.
Try to use the friction property within the leaf builder, and play with the number and position of inter-leaf contacts until the hysteresis matches test data. This approach may have some robustness issues and also I am not sure how much it will affect the solve time for a full-vehicle model.

Best,

Christopher Fadanelli

Hi @EduardoMRech,

You could use the MS-OS co-simulation—I’ve considered that approach as well. However, it may require some time to run (depending on the type of analysis), and you might need to tweak certain solver settings, such as h_max. In the OS model, I would recommend modeling the eyes and bushings directly. This way, when connecting to MS, you only need to use three ball joints per eye to fix the OS body to the Vehicle Body.

From various MS-OS simulations I’ve ran, I strongly suggest connecting the OS body to a body with high mass and inertia—such as the Vehicle Body. If all connected bodies have very low mass, it can cause numerical instability.

I do have a few questions about your test setup: what type of road event are you planning to run? Currently, this workflow is best suited for events where the vehicle remains on a straight path. When the model is relaunched from a sequential simulation, the steering becomes locked—this issue is still under investigation.

Or will this be a leaf spring test rig analysis?

Best,

Christopher Fadanelli

Thank you for the update. Test rig, K&C and specific maneuvers can be done with MS-OS co-simulation. Like I mentioned, it will increase your simulation time. Will you get the most accurate results, yes but it will take some significant computing power. I hope all of these options will provide useful aid!

Best,

Christopher Fadanelli

All comments

Hope this helps!

Christopher Fadanelli

Thanks for the reply, @Christopher_Fadanelli!

I was wondering if it would be possible to use a Flexbody for the leaf spring model with the material defined in Optistruct.

Would that be possible?

Best regards,

Eduardo Miorelli Rech

Of course @EduardoMRech!

That is a potential option. I’m picturing the composite leaf spring to look something like this:

Best,

Christopher Fadanelli

@Christopher_Fadanelli,

Thanks a lot for the suggestions, i'll definitely try out the approach you mentioned with flexbodies and load export.

Just so you know, my main objective is to study the implications of hysteretic behavior in composite leaf springs on vehicle dynamics. Maybe linearity could pose a challenge to my analysis, right?

Best,
Eduardo Miorelli Rech

Yes linearity can pose an issue with the hysteresis. Typically I suggest to use the midline of the curve. There are a couple of options (will involve a lot of iterative work):

Convert the hysteretic area of the leaf spring into an equivalent viscous damping coefficient. There are some papers that show how to do it. Then include this damping in a dummy spring damper entity between the axle and chassis, most likely a torsional one at the leaf ends. This approach will likely result in a more robust model that solves quickly, but needs some math calculations.
Try to use the friction property within the leaf builder, and play with the number and position of inter-leaf contacts until the hysteresis matches test data. This approach may have some robustness issues and also I am not sure how much it will affect the solve time for a full-vehicle model.

Best,

Christopher Fadanelli

Hi @Christopher_Fadanelli,

Thanks for the suggestions on using the equivalent viscous damping coefficient and friction, I'll try those!

Just to confirm: since my goal is to capture the viscoelastic hysteresis of the composite leaf spring, wouldn't a co-simulation between OS and MS, like in your post (https://community.altair.com/discussion/63250/implementing-an-nonlinear-lower-control-arm-motionsolve-optistruct-co-simulation), be a viable option?

I suppose that, if so, the computational effort would be significant, but it seems to be a robust solution as long as enough computing power is available.

Best regards,

Eduardo Miorelli Rech

Hi @EduardoMRech,

Or will this be a leaf spring test rig analysis?

Best,

Christopher Fadanelli