topic Re: Simulating leaf spring, unable to get sliding input for force in Fusion Design, Validate & Document Forum

Simulating leaf spring, unable to get sliding input for force

phillipJSCHJ — Fri, 23 Feb 2024 19:45:56 GMT

Looking to play with simulating leaf springs, there isn't any documentation that I've found so been experimenting. Attached is a video and the F3D file.

Basically, the issue I see is that I can't get the load to move in a non-linear motion, so the leaf wraps up at the fixed main eye and distorts the floating side on the shackle. In leaf springs, as they compress, the center point of the spring moves away from the fixed main eye but in Fusion I can only get it moving on the Z-axis.

Seems like the shackle is pivoting correctly (revolute joints between each pivot with a pin constraint on the loose bolt) and it seems like the main eye is rotating on its pin constraint. I've tried adding an object with both a sliding and separation contact point so that the leaf itself can float, but the simulation treats them as bonded in practice. I've tried square and round landing pads. It seems really close to working out if I can get the load to move with the leaf, and I'd like to not have to use a paid Quasistatic event sim.

Looking to achieve a study similar to this: https://www.youtube.com/watch?v=ABLXevRvqfM

Re: Simulating leaf spring, unable to get sliding input for force

John_Holtz — Tue, 27 Feb 2024 14:19:50 GMT

Hi @phillipJSCHJ

First, you are not going to get accurate results using a static stress analysis. Static stress is a linear analysis that is limited to small displacements, small rotations, and constant stiffness. The rotation of the shackle is large (more than a few degrees), and I would expect the stiffness of the spring to change as it deflects. All of that is ignored in your analysis. (The only thing the animation does in the linear static stress is display the one result you have, the displacement for 10000 lb load, in increments of 10%, 20%, ... 100%.) You need to run the analysis as nonlinear static stress.

All types of static analysis require all the parts to be statically stable. The sliding contact between the pad and spring would allow the pad to slide an infinite distance in X and Y. That is what causes the error about the model not being properly restrained when using sliding contact.

The next challenge is modeling the pin between the spring and shackle to allow rotation. In the current setup, that is bonded. You will need to add another body: a pin that connects the spring to the shackle. Bond the pin to the shackle (or just make the pin part of the shackle) and use sliding contact between the pin and spring.

Let us know if you have any questions.

John

Re: Simulating leaf spring, unable to get sliding input for force

phillipJSCHJ — Tue, 27 Feb 2024 16:34:10 GMT

Then that requires paying for features in software that we already pay a... yearly subscription for. 🙂

As much as possible, I try not to support F360's increasingly toxic business practices. It's stuff like this that's causing me to cross-train to Solidworks over the long-term. Being charged per-study is an absolute cash grab, and it's reprehensible what Autodesk has done to former lifetime licenses.

Mostly using this to dick around and play with some things in anti-wrap bar geometry and so-on, not using this as an exact study by any means for interacting with the spring rates through travel. I've fixed most of my issues, getting the shackle and spring to pivot (revolute joints were used) is the only current issue. The pusher pad tracks straight, the spring is starting to take a predictable arc from the main eye now that it can slide. I'll give your suggestion a try.

Re: Simulating leaf spring, unable to get sliding input for force

John_Holtz — Tue, 27 Feb 2024 16:33:08 GMT

Yes, the analysis is coming along.

Note that joints setup in the Design workspace to define the position and motion between components of an assembly have no effect in the Simulation workspace. The revolute joint needs to be replicated with contact for the simulation.

Let us know how it turns out.

John

Re: Simulating leaf spring, unable to get sliding input for force

phillipJSCHJ — Tue, 27 Feb 2024 19:54:47 GMT

Got it working. I had to add some clearance between the leaf and shackle, Fusion kept adding bonded contacts there and once spaced out and using your assembly method (the pin is apart of the shackle with the matching concave feature of the leaf set as a sliding contact to create the hinge point), and it seems to be functioning. It still seems like the shackle is stretching, but I can now put a normal load into it, run it with the actual deformation shown, and it's behaving predictably.

Thanks again. This is just a way to visibly tinker with a few things, but I intend to draw up a factory leaf pack to see if it'll behave.