Surface contact

[banksie]

Hello,

I'm using calculix to model a railway track panel that is being lifted between the bogies of an on-track machine. To model the track support structure (i.e. the ballast) I have created a surface on which the track sits. I was hoping that this arrangement would provide the stiffness I require to support the track, but leave the track unconstrained when I apply a load to lift it from the ground. However, what I am finding is that the track is being constrained to the surface at the nodes defined as contact points. Is there anyway to prevent this and allow the contact nodes to come away from the contact surface?

Regards

Rob

 

[chris9]

It sounds like you have applied 'no separation' or 'bonded' contact elements. Try 'frictionless' contact instead and this should allow separation.

Chris

http://www.value-design-consulting.co.uk

 

[banksie]

Yes, that's what I'm thinking, but I can't find an option for this in Calculix. Below is the section of my input code dealing with the Contact. I've specified the ballast as the independent surface (a single 8 node brick element) and the nodes of the track (constructed from 3 node beam elements) as the dependent surface. The only option I can find in Calculix for specifiying the contact type is the *SURFACE BEHAVIOUR keyword, but this seems to only be for setting the parameters for hard or soft contact.

*SURFACE,NAME=Smast
Ebal,S2
*SURFACE,NAME=Sslav,TYPE=NODE
Nslav
*CONTACT PAIR,INTERACTION=SI1
Sslav,Smast
*SURFACE INTERACTION,NAME=SI1
*SURFACE BEHAVIOR
1.5351e-7,.2

 

[chris9]

Mixing beams and bricks for contact problems is not a good idea unless you are sure your software can handle it. Try using just bricks for both and it should be OK.

Chris

http://www.value-design-consulting.co.uk

 

[goncho]

You need a software which support at least non-linear materials then you could define an elastic modulus in compression and other with a small slope (non zero for convergence issues)in tension. Them, use this non-linear material for the track.