Hello, I am modeling a nonlinear compression spring in OptiStruct using CBUSH + PBUSH + PBUSHT + TABLED1. I want to know how to apply initial compression preload in Optistruct. My setup (Example): * Total system has 16 physical wave‑springs. * In FEA, each physical spring is modeled as 1 CBUSH element, so I have 16 CBUSH elements total. * Physical test data (total spring ring):* Free length spring * 100 N @ 1 .83 mm compression (Assembled position of springs) * 162 N @ 3 .23 mm compression (Engaged position) * Since I have 16 elements, force is divided per element:* 1.83 mm → 6.25 N per element * 3.23 mm → 10.16 N per element I have modeled springs in engaged position. Can anyone explain about how should i create spring properties for this. my load is applying pressure on Piston plate.

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How to correctly apply preload in CBUSH + PBUSH nonlinear spring using PBUSHT and TABLED1 (OptiStruc

Hello,
I am modeling a nonlinear compression spring in OptiStruct using CBUSH + PBUSH + PBUSHT + TABLED1. I want to know how to apply initial compression preload in Optistruct.

My setup (Example):

Total system has 16 physical wave‑springs.
In FEA, each physical spring is modeled as 1 CBUSH element, so I have 16 CBUSH elements total.
Physical test data (total spring ring):
- Free length spring
- 100 N @ 1 .83 mm compression (Assembled position of springs)
- 162 N @ 3 .23 mm compression (Engaged position)
Since I have 16 elements, force is divided per element:
- 1.83 mm → 6.25 N per element
- 3.23 mm → 10.16 N per element

I have modeled springs in engaged position.

Can anyone explain about how should i create spring properties for this. my load is applying pressure on Piston plate.

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solon

Hello,

Define the force–displacement relationship for the CBUSH element in PBUSHT. To introduce a preload, shift the force–displacement curve horizontally (to the right or left, as required) so that the CBUSH carries a nonzero force at zero displacement.

Ayyappa_J

Hi..Could you please define an force displacement curve for above example or any other for a preloaded compression spring.?

solon

At 0 mm deflection, the spring already carries an initial preload force F0.
Therefore, the force–deflection relationship for the spring is linear and can be written as:

F = F₀ + k*x

where F is the spring force, k is the spring stiffness, and x is the deflection from the preloaded position.

PBUSHT-TABLE will look like this:

I have attached a small example for your reference:

CBUSH_cable.fem

Ayyappa_J

I am confused about compression and Tension here. As i am modeling compression spring (it should have 0 stiifnees in tension) then it should have more force for -1mm rather than 2.8N..am i correct?

(i am referring the above example you wrote).

solon

Tension is U > 0 and Compression is U < 0 where U = U(GB) - U(GA) in CBUSH element coordinate system: GA/GB are grid points on CBUSH. In the example i shared the preload is tensile based on the setup.

Compressive preload would shift the curve like this:

Ayyappa_J

I have defined compressive spring as above, is it correct?

Or do i need to change the force direction?