hardingfv32 wrote:Question: I don't see how the separation of the upper element in "C" helps increase downward deflection. It would seem like the top element would be needed to get a non-linear increase in movement. This layout could in fact be non-linear, but it would seem to be the opposite of what we are after.
Where am I going of track?
Brian
richard_leeds wrote:Tim, I don't think that works as you describe.
All the load is carried by the bottom part, the top part merely applies a pre-compression load but doesn't carry any of the externally applied load.
Hence the deflection is always dependent on the stiffness of the bottom element, and that is constant.
I understand where you are both coming from. It is not very intuitive how the top plate affects the stiffness but it most certainly does. It looks like it is "pushing" the lower plate down, therefore dropping the stiffness doesnt it?. Explaining it without formulas is prectically impossible.
The bottom plate is easy to understand. It start with a preload force pushing up against the top plate, and as it deflects down, the upwards "restoring force" increases.
The top plate starts with a preload force pushing down, but as the plate deflects down the preload force pushing down decreases (because the plate is going back to its original state).
This is the same as adding a net upwards force to the top plate due to the deflection
So you have the two plates, both producing a net upwards
change in force due to a downward deflection. Only one is doing it by increasing an already present upwards force (bottom plate) while the the other is doing it by reducing an already present downward force.
Tim
