Learning Forum

[rmgpliz]

Hi all, 

I am trying to set up a non-linear spring between two nodes of one body, to see how the spring would deform the body. I have coded the following:

! --- Nonlinear spring definition (COMBIN39) ---

et, _sid, 39              ! Element type: COMBIN39 (nonlinear spring)

keyopt, _sid, 4, 1        ! Positive force = compression

 

! Force–Deflection pairs (in N and mm)

r, _sid, 0, 0, 4.898, 10, 5.5478, 20.248, 6.0594, 31.5

rmore, 6.8578, 46, 8.8298, 56, 11.3864, 63, 13.9936, 70

 

I have the experimental force-displacement curve values, and I'm trying to implement that into the simulation. My first problem is that, defining those Force-Deflection pairs, no deformation happens. Usually, when using linear springs, just by defining the stiffness, deformation occurs, because the spring is compressed from the very first beginning. But when changing the spring properties for it to be non-linear, nothing happens. Could please someone help? 

 

Thank you!

[Erik Kostson]

 

 

 

Hi

One can apply a nonlinear spring (data) in mechanical natively (no need for commands) – under longitudinal stiffness choose tabular (instead of constant) and insert the spring nonlinear (nl) data. Make sure you define both sides of the nl curve (so tension and compression). That will create a combin39 in the background (ds.dat). Finally keyopt(4) = 1 that is just 3D spring with UX,UY,UZ, and not compression is pos. force (actually compression is negative and tension positive in the spring force).

I would sugest aslo to make a simple model and to make sure that the force in the spring matches what you input (just displace it and look at spring force).

All the best

 

 

 

[rmgpliz]

Hi Erik, 

Thanks for your comment. The following is my set up:

So I'm not defining any displacement. Just the preload of the free length - this is usually enough when the stiffness is constant. In terms of my curve, the following curve is the one I want to characterise:

Because of it's bilinear nature, it is not possible to do it in the tabular way / or I can only focus on the unloading part. Any suggestions?