Friction
Both explicit cracks and multimaterial mode MPM can model frictional contact between the surfaces.
Introduction
Contact mechanics between surface can be model as frictionless sliding, Coulomb friction with a surface coefficient of friction, or stick contact (no sliding). In frictionless sliding, the tangential surface force is zero while the normal forces is determined by the amount of contact. In frictional sliding, the magnitude of the tangential force is related to the magnitude of the normal force by:
[math]\displaystyle{ f_t = \mu f_n }[/math]
where μ is the coefficient of friction. But, if the induced tangential force from surface motion is less than this value (e.g., because fn is low) the the contact is modeled as stick contact instead. In stick contact, the two surface move in the center-of-mass velocity field as if there were one material, but only as long as they remain in contact.
Friction on Explicit Cracks
Explicit cracks in NairnMPM can model frictional contact. To choose the default frictional contact options for cracks in scripted file, use the command
Friction (frict)
In XML files, the default frictional contact properties for cracks are define with a <Friction> command within the <Cracks> element in the <MPMHeader>:
<Friction>(frict)</Friction>
The meaning of (frict) is described below.
The above commands set the default frictional contact properties for crack surfaces. When a simulation only has only one crack, this setting is enough. For simulations with more than one crack, you can set different frictional properties, or cracks with frictional contact with cracks as interfaces, by settings available when defining the cracks.