Wet Cohesion

1- Linear irreversible cohesion force model in MercuryDPM referred to as IrreversibleAdhesive (IrreversibleAdhesiveSpecies, IrreversibleAdhesiveInteraction).

Wet cohesion is due to liquid bridges between particles in contact or close proximity. If the system is in the pendular regime (liquid fills less than 30 % of void space), liquid bridges form between particle pairs only; for higher liquid fraction, the three-particle liquid bridges or suspensions need to be considered. Liquid bridges between particle pairs typically have a range smaller than a particle diameter, so they are short-ranged. The liquid bridges form from liquid on the particles surface when two particles come into contact, but require a certain separation distance to separate again, so these forces are irreversible (hysteretic).

A simple linear irreversible adhesive force can be implemented as:

\( f_{ij}^{nc} = \begin{cases} -f_{ij}^{nc, max} & \quad \text{if} \quad \delta{ij}^{n} > 0 \\ -f_{ij}^{nc, max} - k_c \delta_{ij}^{n} & \quad \text{after contact, if} \quad -f_{ij}^{nc, max}/k_c\leq \delta_{ij}^{n} < 0 \\ 0 & \quad \text{else} \end{cases} \)

Header:

#include "Species/AdhesiveForceSpecies/IrreversibleAdhesiveSpecies.h" 

Interaction force:

void IrreversibleAdhesiveInteraction::computeAdhesionForce() 

The model parameters are set using IrreversibleAdhesiveSpecies member functions.

Unit Test: AdhesiveForceUnitTest.cpp

References:
Liquid bridge:
1- C. D. Willett et. al., Capillary bridges between two spherical bodies

2- S. Roy et. al., Micro–macro transition and simplified contact models for wet granular materials