The Bonding V2 contact model is used to bond particles with a finite-sized 'glue'
bond.
This bond can resist tangential and normal movement up to
a maximum normal and tangential shear stress, at which point the bond breaks. Thereafter
the particles interact as hard spheres. This model is based on the works of
Potyondy and Cundall
2004. This model is particularly useful in modeling concrete and rock
structures.
Bonds are created based on two methods - ‘current time’
or ‘fixed’. Once you have selected the Bonding V2 model, these options are displayed
in the Factory creating the Bulk Material or Meta-Particles.
- Current time allows the dynamic creation of bonded materials.
- Fixed time allows the creation of bonded material at one user-defined point
in time.
If the Bulk Material Active Bonds are defined and the Particles that comprise
the Bulk Material are in contact at the bond creation time, the bonds are formed
according the bond parameters. This occurs once per simulation for each particle
pair. Once the bond time has passed, no new bonds will be formed.
You can also use a custom API factory to create
material and use the Bonding V2 model. The API factory can be set to assign a Custom
Property with the name CREATIONTIME = "Bond Creation Time”. The factory must then
assign a value to the custom property equal to the current simulation time. EDEM will then create bonds between particles if the
particles are in contact and both particles have a Custom Property CREATIONTIME
value equal to the current simulation time. The custom property must be defined with
1 element and unit of eTime.
After bonding, the forces
(Fn,t)/torques (Tn,t) on the particle are set to zero and are
adjusted incrementally every Time Step as follows:
Where
RB is the radius of the glue. This value is
set as the radius of the smallest particle out of a contact pair multiplied by the
Bonded Disk Scale value that you have set.
Sn,t are the normal and
shear stiffness respectively. If the Normal or Tangential Range value is set to 0
N/m3 then the stiffness value is assigned based on the bond configuration value.
Otherwise the bond is assigned a value randomly distributed between the Stiffness
value + or – the range value. This provides a linear distribution of bond stiffness
values for a given material.
δt is the Time Step. vn,t are the
normal and tangential velocities of the particles and ωn,t the normal and
tangential angular velocities.
The bond is broken when the normal and
tangential shear stresses exceed a predefined value.
These bond forces/torques are in addition to
the Base Contact Model. Since the bonds involved in this model can act when the
particles are no longer physically in contact, the contact radius must be set to
higher than the actual radius of the spheres. This model may only be used between
particles.
Select an active bond and then specify the Bond Formation method
and the following parameters:
Interaction |
Configurable Parameters |
Particle to Particle |
Normal Stiffness per unit
area Indicates the tensile/compressive
stiffness along the bond’s principal
axis. Normal
Range Indicates the applied Normal
Stiffness per unit area value assigned to the bond pair is a
value randomly distributed between the Normal Stiffness
value + or – the Normal range value. Shear
Stiffness per unit area Indicates the
Shear stiffness in the orthogonal plane to the bond’s
principal axis. Shear
Range Indicates the applied Shear
Stiffness per unit area value assigned to the bond pair is a
value randomly distributed between the Shear Stiffness value
+ or – the Shear range value. Critical
Normal Stress Indicates the maximum
normal stress the bond can withstand before it
fails. Critical Shear
Stress The maximum tangential stress
the bond can withstand before it
fails. Bonded Disk
Scale The radius of the cylindrical bond
between the particles will be equal to the smallest particle
radius in a bond pair multiplied by the bonded disk scale
value. Torque Feedback
- Enables the Bond Torque to be returned to the
Particle.
- Set the bond stress and stiffness values to
represent the material that is been modeled. A high
stiffness value will produce high bond forces and
stresses. A lower than normal Time Step may be
required to accurately capture these high
forces.
- When the Bond Formation Time is reached, all defined
particles in contact will be bonded together. Before
this time, particles interact based on the
Hertz-Mindlin contact model.
- A bond between two particles will cease to exist
whenever one or both of the bonded particles leave
the simulation domain. If periodic boundaries are
applied when the particle leaves the domain, then
the particle will exist on the opposite side of the
domain; in this case the two particles will remain
bonded across the periodic boundary.
- When Torque Feedback is selected, the bonded
structure has a greater resistance to bending when
considering a bond between two spheres, for a bonded
structure where rotation is limited this setting has
less impact.
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