cohesion model sjkr/time_dependent

Purpose

Modelling material cohesion using a modified version of the simplified Johnson-Kendall-Roberts (SJKR) cohesion model.

Syntax

cohesion sjkr/time_dependent [other model_type/model_name pairs as described here ] settings keyword values

zero or one keyword/value pairs may be appended after the keyword settings (after all models are specified)

tangential_reduce values = 'on' or 'off'
  on = tangential model does not see normal force computed by this model
  off = tangential model does see normal force computed by this model

Associated material properties

Material interaction properties

cohesionEnergyDensity ( $k$ ): cohesion energy density between the two materials [energy/length^3].
cohesionEnergyDensityModifier ( $m$ ): time-dependent modifier of the cohesion energy density [ $\cdot$ ]. It is provided via lookup table.

Description

This model can be used as part of pair gran and fix wall/gran.

The difference between this model and the SJKR is that the cohesion energy density is multiplied by a time-dependent coefficient:

$F = k m(t) A$

where $F$ is the normal cohesion force and $A$ is the particles contact area, calculated assuming sphere-sphere contact as (http://mathworld.wolfram.com/Sphere-SphereIntersection.html).

$A = - \frac{\pi}{4} (( d - r_i - r_j) (d + r_i - r_j) (d - r_i + r_j) (d + r_i + r_j) )/(d^2)$

where $d$ is the distance between the particles $i$ and $j$ and $r_i$ and $r_j$ are the particle radii.

The optional keyword tangential_reduce specifies if the tangential force model should be affected by the additional normal force exerted by this model. If set to ‘off’ (which is default), then the tangential force model will take into account the extra normal force generated by this model; hence, the tangential force model will be able to transmit a larger amount of tangential force. If set to ‘on’, then the tangential model will not take the normal force from this model into account, typically leading to a lower value of tangential force (via the Coulomb friction limit).

Restrictions

The cohesion model has been derived for the Hertzian style, it may note be appropriate for the Hookean styles.

It is not available for atom_style superquadric

Coarse-graining information:

Using coarsegraining in combination with this command should lead to statistically equivalent dynamics and system state.

Default

tangential_reduce = ‘off’