ContactForceT_SpringSlider class
Contents
Description
This is a sub-class of the ContactForceT class for the implementation of the Spring-Slider tangent contact force model.
This model assumes that the tangent contact force has an elastic component
, provided by a linear spring, and a friction component
, provided by a slider, which limits the total force according to Coulomb law.



The tangent stiffness coefficient
can be computed as a function of the normal stiffness coefficient
and the effective Poisson ratio
:

The friction coefficient
must be provided.
Notation:
: Tangent direction between elements
: Tangent overlap
: Time rate of change of tangent overlap
: Normal contact force vector
References:
- R.D. Mindlin. Compliance of elastic bodies in contact, J. Appl. Mech., 16(3):259-268, 1949 (stiffness coefficient formula)
classdef ContactForceT_SpringSlider < ContactForceT
Public properties
properties (SetAccess = public, GetAccess = public)
% Formulation options
auto_stiff logical = logical.empty; % flag for computing stiffness coefficient automatically
% Contact parameters
stiff double = double.empty; % stiffness coefficient
fric double = double.empty; % friction coefficient
end
Constructor method
methods
function this = ContactForceT_SpringSlider()
this = this@ContactForceT(ContactForceT.SPRING_SLIDER);
this = this.setDefaultProps();
end
end
Public methods: implementation of super-class declarations
methods
%------------------------------------------------------------------
function this = setDefaultProps(this)
this.auto_stiff = true;
end
%------------------------------------------------------------------
function this = setCteParams(this,int)
if (this.auto_stiff)
if (~isempty(int.cforcen))
% Assumption: average poisson ratio
this.stiff = (1-int.avg_poisson)/(1-int.avg_poisson/2) * int.cforcen.stiff;
else
this.stiff = 0;
end
end
end
%------------------------------------------------------------------
function this = evalForce(this,int)
% Force modulus (elastic and friction contributions)
fe = this.stiff * int.kinemat.ovlp_t;
if (~isempty(int.cforcen))
ff = this.fric * norm(int.cforcen.total_force);
else
ff = 0;
end
% Limit elastic force by Coulomb law
f = min(abs(fe),abs(ff));
% Total tangential force vector (against deformation and motion)
this.total_force = -f * int.kinemat.dir_t;
end
end
end