Tangential contact

The Tangential contact tab governs sliding along the contact surfaces — how much shear the interface transmits before it slips.

Friction model

Model	Parameters
Friction less	—
Coulomb	tan(delta), Adhesion c
Mohr-Coulomb	tan(delta), tan(theta), Adhesion c
Hypoplasticity_numgeo	16 parameters, from d_s and kappa through to chi

Friction less transmits no shear at all, so the surfaces slide freely. It is the default for a new interaction.

Coulomb and Mohr-Coulomb describe a limiting shear stress from a friction coefficient and an adhesion. tan(delta) is the tangent of the interface friction angle, not the angle itself.

Hypoplasticity_numgeo is an advanced interface model for cyclic and large-displacement problems and needs a full parameter set.

Field	Choices	Meaning
Friction model	as above	The interface friction law
User defined friction	yes, no	Supply the friction law yourself
Tangential stiffness	Stiffness factor, Constant	How the elastic stick stiffness is given
Value		The stiffness factor, or the constant stiffness

The tangential stiffness fields apply to Coulomb and Mohr-Coulomb only, since those are the models with an elastic stick regime before slip.

Validation

The tangential-stiffness value is required when a stiffness definition is selected, and every parameter of the chosen friction model must be filled. Pressing Apply & Save with one missing shows a warning naming the field.

See Interaction in the numgeo reference manual.