Contact Laws

Introduction

NairnMPM and OSParticulas implement contact physics on crack surfaces and between materials in multimaterial mode to model friction or [[#Imperfect interfaces|imperfect interfaces]. The contact mechanics is determined by selecting a contact law. The currently available contact laws are divided into two type — frictional contact law and imperfect interface laws. These default crack contact or for material-material contact are selected by using the ContactCracks or ContactMM commands. if needed, the default contact laws can be customized for each individual crack when defining a new crack or can be customized for each material pair by using the Contact material property. This section documents all the possible contact laws.

All contact laws are using a Material command block. Within that block all contact law properties are set using property commands. Refer to each contact law type to learn about its possible properties.

Frictional Contact Laws

Frictional contact laws give the sliding shear traction, S_slide, as a function of the normal traction, N, the contact area, A_c, the relative sliding velocity, Δv,and possible other parameters, or:

      [math]\displaystyle{ S_{slide} = f(N,A_c,\Delta v,...) }[/math]

Given any frictional law, the shear traction applied at any node is given by:

      [math]\displaystyle{ S_{resultant} = \min(S_{slide},S_{stick}) }[/math]

where S_stick is the shear traction needed for tangential motion of the two surface to move together (i.e., to stick). In other words, if the shear traction calculated for frictional sliding is greater than the traction required for surfaces to stick together, then the surface will stick. Once that sticking shear traction exceeds S_slide, the surfaces will slide with the given sliding traction. More details on friction in MPM can be found in Nairn and Smith (2016).

The available contact laws are listed in the following table. See each law to learn about the function used to determine S_slide and about the parameters required to use that law.

Name	Number	Description
IgnoreContact	60	ignore contact or revert to single material mode
CoulombFriction	61	contact by simple Coulomb friction
AdhesiveFriction	63	contact by Coulomb friction with adhesion