cohesion model wet_fiber

cohesion model fiber_buckle

cohesion model fiber_plastic

cohesion model wet_fiber_buckle

cohesion model wet_fiber_plastic

Purpose

Advanced fiber contact models for plastic deformation and cohesion between fibers.

Syntax

cohesion wet_fiber [other model_type/model_name pairs as described here ] general_keyword general_value wet_keyword wet_value
cohesion fiber_buckle [other model_type/model_name pairs as described here ] general_keyword general_value deformation_keyword deformation_value
cohesion fiber_plastic [other model_type/model_name pairs as described here ] general_keyword general_value deformation_keyword deformation_value
cohesion wet_fiber_buckle [other model_type/model_name pairs as described here ] general_keyword general_value wet_keyword wet_value deformation_keyword deformation_value
cohesion wet_fiber_plastic [other model_type/model_name pairs as described here ] general_keyword general_value wet_keyword wet_value deformation_keyword deformation_value

zero or more general_keyword/general_value pairs may be appended to the end (using the settings keyword)

keep_original_shape general_value = 'on' or 'off'
    on = fibers will attempt to return to their original shape
    off = fibers will attempt to return to a straightened form [default]

zero or more wet_keyword/wet_value pairs may be appended to the end (using the settings keyword)

tangential_reduce wet_value = '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

zero or more deformation_keyword/deformation_value pairs may be appended to the end (using the settings keyword)

saveVanMisesStress deformation_value = 'on' or 'off'
    on = saves the van Mises stress value for each sphere
    off = does not save the value

Associated material properties

Material interaction properties

cohesionEnergyDensity ( $c_{ED}$ ): The cohesion energy density for wet fiber models [energy/length^3]
yieldStrengthFiber ( $\sigma_Y$ ): The yield strength for the buckle and plastic models [pressure]
deformationTimeScaleFiber ( $t_f$ ): characteristic fiber deformation rate, or the inverse of the time scale with which deformation occurs (only plastic models) [1/time]

Description

This model can be used as part of a particle_contact_model.

These models are extensions of the basic fiber model. Thus, all five models require the same material properties as the basic fiber model. The extension consists of two main features, the first of which concerns sticky or wet fibers. It basically adds a cohesion model sjkr model on top in order to allow fibers to stick together. Note, there even though the model is called wet_fiber it does not include any liquid transfer or liquid bridge like model.

The second main feature is related to deformation of the fiber and comes in two flavours, buckling (fiber_buckle) and plastic deformation (fiber_plastic). The first, buckling, allows the fiber to buckle if a stress threshold is exceeded whereas the plastic deformation mode will allow the fiber to undergo plastic deformation. Both these two deformation models can be combined with the wet fiber model using the wet_fiber_buckle and wet_fiber_plastic model.

Both deformation models compute the local van Mises stress

$\sigma_{vM} = \sqrt{\frac{1}{2}\left(\sigma_n^2 + \sigma_t^2 + (\sigma_n - \sigma_t)^2\right)}$

where $\sigma_n$ and $\sigma_t$ are the normal and tangential stresses of a sphere-sphere interaction inside a fiber, respectively.

In case of the fiber_buckle model and if the van Mises stress exceeds the yield strength (see below) the fiber is considered to be broken between the two interacting spheres.

If the fiber_plastic model is chosen and if the van Mises stress exceeds the yield strength then the fiber will start to exhibit plastic deformation which relaxes the tangential fiber from the basic fiber model. This will cause the fiber to deform and retain its form once the stress is removed. The rate with which the tangential spring is relaxed can be controlled by a deformation time scale (see below).

The wet_fiber model requires the definition of a cohesion energy density for all material and material interaction properties using the cohesionEnergyDensity keyword. This value is given in $Energy/length^3$ units.

The two deformation models require the definition of a yield strength for all material and material interaction properties using the yieldStrengthFiber keyword. This value is given in $Force/length^2$ units. The fiber_plastic model requires an additional property with keyword deformationTimeScaleFiber given in $1/time$ units.

The optional keyword tangential_reduce used in the wet_fiber models defines if the tangential force model should “see” the additional normal force exerted by this model. If it is ‘off’ (which is default) then the tangential force model will be able to transmit a larger amount of tangential force If tangential_reduce = ‘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)

The optional keyword saveVanMisesStress used in the two deformation models writes the current maximal van Mises stress value of all interaction a sphere has into a property atom which can be accessed using its id vanMisesStress.

If keep_original_shape is not enabled a fiber will always attempt to relax itself into a completely straight state as long as there is no plastic deformation of the fiber. If it is enabled then the fiber will try to relax into the state it had upon insertion plus any additional plastic deformation.

Restrictions

This model cannot be used as a wall contact model.

Coarse-graining information:

Using coarsegraining in combination with this command might lead to different dynamics or system state and thus to inconsistencies.

Default

tangential_reduce = ‘off’ saveVanMisesStress = ‘off’