Explaination of the Stiffness property in a Gap element.

[jxc]

I am currently working through an initial contact analysis problem & I am looking for an explaination of the stiffness property used in a gap element. It would also be helpful if someone could provide some typical values.

The software I am using supports nonlinear static & dynamic analysis, I am using a NLS.

Please let me know if additional information is necessary.

Thank all in advance, JXC

 

[brad]

There are two approaches for contact--penalty stiffness or lagrange multipliers.

Lagrange multipliers are the "exact" solution--when the gap element closes, a constraint is applied to not allow overclosure. From a "stiffness" perspective, this behaves as a step function--if the gap is open, there is discretely zero stiffness. When the gap closes to zero, there is a step function whereby the "stiffness" is effectively infinite (the constraint is imposed).

Penalty contact instead uses a very stiff internal spring. So for example, when the gap is open there would again be zero force but at some point (typically zero opening, but it could be a small opening amount) a very stiff internal spring is essentially added. This penalty stiffness should be high enough to disallow significant overclosure, but not so stiff as to introduce serious matrix conditioning problems. As far as what this value is, that is generally code-dependent.

Brad

 

[jxc]

Bradh,

Thanks for the input it is a help.

jxc