Non linear spring

[takbir911]

Hello everyone,

I just joined this group, a newbie in design and abaqus user. I have a question regarding nonlinear spring in abaqus. I have heard in this forum and others that we must use axial connector section and define force displacement parameters. To which do these refer to? the spring or the force I input in my model? I have attacked a screenshot of the model with details and also the obd file.
My question is, lets say for an input force upto 10N from 1N, i desire zero output displacement. At 11N or 10.1 whatever, i want the spring to be linear. In the attached jpg, I've mentioned the input and output ports and spring position.
In the attached model, I have input some parameters for spring trying to simulate the above condition. Have i written the correct code or not?
Please help.

Thank you in advance, Cheers.

 

[IceBreakerSours]

In your force-displacement behavior, you are allowing 10 units of displacement before any resistance is offered! I divided the displacement column by 10 and the model worked. I don't know if that is "okay" because I am not aware of the details, application, etc. but it seems alright.

But the "legs" cross each other after some load, you may either need to stiffen the spring or introduce interaction properties at appropriate locations.

Bottomline: Your force-displacement curve is inappropriate; check your units.

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[takbir911]

Hello IceBreakerSours
Thanks for your reply. I am glad that I am somewhat close to the solution I desire.
But how did you realize that I have zero resistance for 10mm displacement? I actually wanted to define zero displacement of the spring while the output port moves 2mm freely and then have a stiffness. Something analogous to real life scenario where when you try to touch an object. Have I defined the parameters the other way around?
Regarding the legs crossing each other, yes I have defined interaction parameter which hasn't been updated in the above attached file.

 

[takbir911]

Suppose I define the parameter like this:-

*Connector Behavior, name=ConnSect-1
*Connector Elasticity, nonlinear, component=1
-1000., 2
0., 0
50., 8.5

What would this imply?

 

[IceBreakerSours]

What would this imply?

Well, what do you think? Did you read the manuals (before using a connector element)? Try the following:

Run a model with just one connector element in it, assign the force-displacement property of your choice, apply a boundary condition and check the connector displacement vs. reaction force. You should request for output variables recommended for connector element set, just so you know. If you don't know what those are, check the Analysis User's Manual.

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[takbir911]

Thanks for the reply IceBreakerSours, yes I've read the manual but I couldn't understand completely.
So in the first OBD file that I attached, have I defined in such a way that till a force of 10N no resistance is applied, and after that some resistance is being applied? Is the force-displacement parameters that of spring or the input force and output port displacement? Forgive me for asking noob questions, I really suck in abaqus.

 

[IceBreakerSours]

Your questions have little to do with ABAQUS and more to do with lack of understanding of the material property (force-displacement) that you assigned to the connector element.

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[takbir911]

No I am unable to understand how to use the connector element. What I'm looking for is that for an output displacement of 5mm I don't want any resistance. But after that I want to have some resistance of 5N/mm stiffness. So if I input as :
*Connector Behavior, name=ConnSect-1
*Connector Elasticity, nonlinear, component=1
0., 5
5., 6
would I be satisfying my condition?
Also could you please throw some light on output variables for connector element?

Thank you.

 

[IceBreakerSours]

Final attempt:

Try to run a model with one connector element in it. Try and play with the force-displacement behavior and find out for yourself. Try and use the Analysis User's Manual to find out which output variables to use.

Good luck.

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083