DomP
Bioengineer
- Jul 30, 2015
- 2
Hi all,
I am currently designing a compact bi-stable spring for its dynamic properties (speed of snapping-through).
I found two previous threads that touched some words about the basics (thread404-133228 and thread404-249650) but I am interested in increasing the asymmetry of it and looking at its dynamic, not only the loads and stresses, something that israelkk mentioned.
As a start let’s take a simple conical Belleville spring with a ratio height/thickness >sqrt(8)=2.83 so that it is in its bi-stable mode. The spring is loaded (inverted) with whatever force, the figures of interest are the required peak force to snap-it back, and the peak speed of snapping-back. How would you address this approach? What would you do to maximise this speed while lowering the snap-back force?
My feeling is that this is linked with the asymmetry of the design: you need a spring that requires an enormous force to load it with a slow speed of transition, in order to require a small force to snap it back which will release the stocked energy and high internal stress with a high speed.
What drives that asymmetry? What material and design would be sensible to have such an inverted spring stable in time?
How is the question expanded when the geometry is no more a simple cone, but a spherical cap/dome with an internal hole, or more cut-through for instance, does it help with the asymmetry?
I don’t thing FE is able to handle these high-transient phenomena of buckling/snapping-through in dynamic mode (to know the speed), does the deflection-load Belleville spring equation is accurate enough to describe the return-snap-though force? Is there another equation that would give some insight at what is happening during the high transient snap-though, in order to assess the speed? And what about when the geometry is no more a perfect conical Belleville spring?
I am just posting question so far to not bias the answers as I am really interested by your perhaps diverse views on the subject. I already biased it with the asymmetry topic, and my view on FE! Thank you for kicking-off the conversation and see where it rolls!
Thank you
Best regards,
DomP
I am currently designing a compact bi-stable spring for its dynamic properties (speed of snapping-through).
I found two previous threads that touched some words about the basics (thread404-133228 and thread404-249650) but I am interested in increasing the asymmetry of it and looking at its dynamic, not only the loads and stresses, something that israelkk mentioned.
As a start let’s take a simple conical Belleville spring with a ratio height/thickness >sqrt(8)=2.83 so that it is in its bi-stable mode. The spring is loaded (inverted) with whatever force, the figures of interest are the required peak force to snap-it back, and the peak speed of snapping-back. How would you address this approach? What would you do to maximise this speed while lowering the snap-back force?
My feeling is that this is linked with the asymmetry of the design: you need a spring that requires an enormous force to load it with a slow speed of transition, in order to require a small force to snap it back which will release the stocked energy and high internal stress with a high speed.
What drives that asymmetry? What material and design would be sensible to have such an inverted spring stable in time?
How is the question expanded when the geometry is no more a simple cone, but a spherical cap/dome with an internal hole, or more cut-through for instance, does it help with the asymmetry?
I don’t thing FE is able to handle these high-transient phenomena of buckling/snapping-through in dynamic mode (to know the speed), does the deflection-load Belleville spring equation is accurate enough to describe the return-snap-though force? Is there another equation that would give some insight at what is happening during the high transient snap-though, in order to assess the speed? And what about when the geometry is no more a perfect conical Belleville spring?
I am just posting question so far to not bias the answers as I am really interested by your perhaps diverse views on the subject. I already biased it with the asymmetry topic, and my view on FE! Thank you for kicking-off the conversation and see where it rolls!
Thank you
Best regards,
DomP
