You can use surface-to-surface contact elements and the node-to-surface contact element in combination with the coupled-field solid elements (PLANE223, SOLID226, SOLID227) and diffusion solid elements (PLANE238, SOLID239, SOLID240) to model diffusion flow normal to the contact surface.
Use KEYOPT(1) on the contact elements to control which degrees of freedom are included. The following diffusion effects can be modeled:
| Contact Element Keyoption | DOFs | Analysis Physics |
|---|---|---|
| KEYOPT(1) = 11 | UX, UY, UZ, CONC, TEMP | Coupled Structural-Thermal-Diffusion |
| KEYOPT(1) = 12 | UX, UY, UZ, CONC, TEMP, VOLT | Coupled Structural-Thermal-Electric-Diffusion |
| KEYOPT(1) = 13 | UX, UY, UZ, CONC | Coupled Structural-Diffusion |
| KEYOPT(1) = 14 | CONC | Single-Field Concentration |
The following diffusive contact interactions are supported:
To take into account the diffusion flow across two surfaces that are in contact or separated by a small gap distance (near-field), you need to specify the contact diffusivity coefficient, which is input as real constant DCC of the contact element.
The diffusion flux density from the contact surface to the target surface is defined as:
where:
| q = the diffusion flux density per unit area |
| DCC = the contact diffusivity coefficient, having units of length3/time for force-based node-to-surface contact, or units of length/time for the traction-based model |
| Cc and Ct = concentration of the contact points on the contact and target surfaces |
A relatively small value of DCC yields a measured amount of imperfect contact and a diffusion discontinuity across the interface. For relatively large values of DCC, the resulting diffusion discontinuity tends to vanish, and perfect diffusive contact is approached.
The contact diffusivity coefficient is input via the DCC real constant on the
contact element. By using tabular input (see Defining Real Constants in Tabular Format),
you can define DCC as a function of temperature (
), pressure (positive PRESSURE index values indicate
compression, negative PRESSURE index values indicate tension), time, and initial
contact detection point location (at the beginning of solution).
For example, you could use tabular input to specify DCC as a function of GAP such that different diffusivity coefficients are applied based on the contact status, whether it is closed contact (positive GAP) or near-field contact (negative GAP). You could also specify a cutoff gap distance beyond which no diffusion flow occurs (DCC = 0).
The USERCNPROP user subroutine is also available for defining DCC. To use this subroutine, you must specify the table name %_CNPROP% as the real constant value. For more information, see Defining Real Constants via a User Subroutine.
When modeling diffusion flow, concentrations for both the contact and target surfaces are required.
For a deformable target surface, the concentration varies along the surface. In this case, the concentration at the intersection between the target surface and the normal from the contact detection point represents the target concentration.
For a rigid target, the concentration on the pilot node (if a pilot node is defined) represents the concentration for the entire rigid target surface.
To model diffusion flow from far-field contact to the environment, you need to specify the following contact element real constants:
DCON is the diffusive convection coefficient.
ABDC is the ambient concentration.
The diffusion flux density for open contact is defined as:
The ambient concentration, ABDC, has units of mass/length3, or it is dimensionless if normalized concentration is defined for the underlying solid elements. The default value of ABDC is 0.
The diffusive convection coefficient, DCON, defaults to 0, which defines the no-diffusion condition for far-field contact. DCON has units of length3/time for the force-based node-to-surface contact model, or units of length/time for the traction-based model.
The DCON and ABDC real constants can be made a function of temperature
(), time, and initial contact detection point location (at the
beginning of solution) by using tabular input (see Defining Real Constants in Tabular Format).
The user subroutine USERCNPROP is also available for defining DCON and ABDC. To use this subroutine, you must specify the table name %_CNPROP% as the real constant value. For more information, see Defining Real Constants via a User Subroutine.