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37.3 Electrical contact properties
• “Electrical contact properties,” Section 37.3.1
37.3.1 ELECTRICAL CONTACT PROPERTIES
Products: Abaqus/Standard Abaqus/CAE
References
• “Contact interaction analysis: overview,” Section 36.1.1
• “Thermal contact properties,” Section 37.2.1
• “GAPELECTR,” Section 1.1.11 of the Abaqus User Subroutines Reference Guide
• *GAP ELECTRICAL CONDUCTANCE
• *SURFACE INTERACTION
• “Specifying gap conductance for electrical contact property options” in “Defining a contact interaction property,” Section 15.14.1 of the Abaqus/CAE User’s Guide, in the HTML version of this guide
Overview
Electrical conduction between two bodies:
• is proportional to the difference in electric potentials across the interface;
• is a function of the clearance between the surfaces;
• can be a function of contact pressure;
• can be a function of surface temperatures and/or predefined field variables on the surfaces; and
• can generate heat at the interface.
See “Coupled thermal-electrical analysis,” Section 6.7.3, and “Fully coupled thermal-electrical-structural analysis,” Section 6.7.4, for details on coupled thermal-electrical and coupled thermal-electricalstructural analyses.
Including gap electrical conductance properties in a contact property definition
You can include electrical conductance properties in a contact property definition for surface-based contact.
Input File Usage: Use both of the following options:
*SURFACE INTERACTION, NAME=name
*GAP ELECTRICAL CONDUCTANCE
Abaqus/CAE Usage: Interaction module: contact property editor: Electrical→Electrical Conductance
Modeling electrical conductance between surfaces
Abaqus/Standard models the electrical current flowing between two surfaces as
J = \sigma_ {g} (\varphi_ {A} - \varphi_ {B}),
where J is the electrical current density flowing across the interface from point A on one surface to point B on the other, \varphi _ { A } and \varphi _ { B } are the electrical potentials on opposite points on the surfaces, and \sigma _ { g } is the gap electrical conductance. Point A corresponds to a node on the slave surface of the contact pair. Point B is the point of the master surface in contact with point A.
You can provide the electrical conductance directly or in user subroutine GAPELECTR.
Defining \sigma _ { g } directly
When the gap electrical conductance is defined directly, Abaqus/Standard assumes that
\sigma_ {g} = \sigma_ {g} (\bar {\theta}, d, p, \bar {f} ^ {\alpha}),
where
\begin{array} { r } { \overline { { \theta } } = \frac { 1 } { 2 } ( \theta _ { A } + \theta _ { B } ) } \end{array} is the average of the surface temperatures at A and B,
d is the clearance between A and B,
p is the contact pressure transmitted across the interface between A and B, and
\begin{array} { r } { \bar { f } ^ { \alpha } = \frac { 1 } { 2 } ( f _ { A } ^ { \alpha } + f _ { B } ^ { \alpha } ) } \end{array} is the average of any predefined field variables at A and B.
Defining gap electrical conductance as a function of clearance
You can create a table of data defining the dependence of \sigma _ { g } on the variables listed above. The default in Abaqus is to make \sigma _ { g } a function of the clearance, d. When \sigma _ { g } is a function of gap clearance, d , the tabular data must start at zero clearance (closed gap) and define \sigma _ { g } as a function of the clearance. The value of \sigma _ { g } remains constant for clearances outside of the interval defined by the data points. If gap electrical conductance is not also defined as a function of contact pressure, \sigma _ { g } will remain constant at the zero clearance value for all pressures, as shown in Figure 37.3.1–1(a).
text_image
Σg d p (a)
line
| p | Σg | | ---- | --- | | d | | | p | |Figure 37.3.1–1 Examples of defining the gap electrical conductance as a function of clearance (a) or contact pressure (b).
Input File Usage: *GAP ELECTRICAL CONDUCTANCE
\sigma_ {g}, d, \theta
Abaqus/CAE Usage: Interaction module: contact property editor: Electrical→Electrical Conductance; Definition: Tabular; Use only clearancedependency data
Defining gap electrical conductance as a function of contact pressure
You can define \sigma _ { g } as a function of the contact pressure, p. When \sigma _ { g } is a function of contact pressure at the interface, the tabular data must start at zero contact pressure (or, in the case of contact that can support a tensile force, the data point with the most negative pressure) and define \sigma _ { g } as \pmb { p } increases. The value of \sigma _ { g } remains constant for contact pressures outside of the interval defined by the data points. If gap electrical conductance is not also defined as a function of clearance, \sigma _ { g } is zero for all positive values of clearance and discontinuous at zero clearance, as shown in Figure 37.3.1–1(b).
Input File Usage: *GAP ELECTRICAL CONDUCTANCE, PRESSURE
\sigma_ {g}, p, \theta
Abaqus/CAE Usage: Interaction module: contact property editor: Electrical→Electrical
Conductance; Definition: Tabular; Use only pressure-dependency data
Gap electrical conductance as a function of both clearance and contact pressure
You can define \sigma _ { g } to depend on both clearance and pressure. A discontinuity in \sigma _ { g } is allowed at d = 0 and p = 0 . Once contact occurs, the conductance is always evaluated based on the portion of the curve that defines the pressure dependence. The gap electrical conductance, \sigma _ { g } , , remains constant for contact pressures outside of the interval defined by the data points. The pressure dependence of \sigma _ { g } is extended into the negative pressure region even if no data points with negative pressure are included.
Input File Usage: Use both of the following options:
*GAP ELECTRICAL CONDUCTANCE
\sigma_ {g}, d, \theta
*GAP ELECTRICAL CONDUCTANCE, PRESSURE
\sigma_ {g}, p, \theta
Abaqus/CAE Usage: Interaction module: contact property editor: Electrical→Electrical Conductance; Definition: Tabular; Use both clearanceand pressure-dependency data
Defining gap electrical conductance to be a function of predefined field variables
The gap electrical conductance can be dependent on any number of predefined field variables, \bar { f } ^ { \alpha } . By default, it is assumed that the electrical conductivity depends only on the surface separation and, possibly, on the average interface temperature.
Input File Usage: *GAP ELECTRICAL CONDUCTANCE, DEPENDENCIES=n
Abaqus/CAE Usage: Interaction module: contact property editor: Electrical→Electrical Conductance; Definition: Tabular, Clearance Dependency and/or Pressure Dependency, Number of field variables: n
Defining \sigma _ { g } using user subroutine GAPELECTR
When \sigma _ { g } is defined in user subroutine GAPELECTR, there is greater flexibility in specifying the dependencies of \sigma _ { g } than there is using direct tabular input. For example, it is no longer necessary to define \sigma _ { g } as a function of the average of the two surfaces’ temperatures or field variables:
\sigma_ {g} = \sigma_ {g} (\theta_ {A}, \theta_ {B}, d, p, f _ {A} ^ {\alpha}, f _ {B} ^ {\alpha}).
Input File Usage: *GAP ELECTRICAL CONDUCTANCE, USER
Abaqus/CAE Usage: Interaction module: contact property editor: Electrical→Electrical Conductance; Definition: User-defined
Modeling heat generated by electrical conduction between surfaces
Abaqus/Standard can include the effect of heat generated by electrical conduction between surfaces in a coupled thermal-electrical and a fully coupled thermal-electrical-structural analysis. By default, all dissipated electrical energy is converted to heat and distributed equally between the two surfaces. You can modify the fraction of electrical energy that is released as heat and the distribution between the two surfaces; see “Modeling heat generated by nonthermal surface interactions” in “Thermal contact properties,” Section 37.2.1, for details.
Surface-based output variables for electrical contact property models
Abaqus/Standard provides the following output variables related to the electrical interaction of surfaces:
ECD Electric current per unit area leaving slave surface.
ECDA ECD multiplied by the area associated with the slave node.
ECDT Time integrated ECD.
ECDTA Time integrated ECDA.
The values of these variables are always given at the nodes of the slave surface. They can be requested as surface output to the data, results, or output database files (see “Surface output from Abaqus/Standard” in “Output to the data and results files,” Section 4.1.2, and “Surface output in Abaqus/Standard and Abaqus/Explicit” in “Output to the output database,” Section 4.1.3, for details).
Contour plots of these variables can also be displayed in the Visualization module of Abaqus/CAE (Abaqus/Viewer).
37.4 Pore fluid contact properties
• “Pore fluid contact properties,” Section 37.4.1
37.4.1 PORE FLUID CONTACT PROPERTIES
Product: Abaqus/Standard
References
• “Contact interaction analysis: overview,” Section 36.1.1
• *CONTACT PERMEABILITY
• *SURFACE
• *SURFACE INTERACTION
• *CONTACT PAIR
Overview
The pore fluid contact property models:
• are often used in geotechnical applications, where pore pressure continuity between material on opposite sides of an interface must be maintained;
• govern pore fluid flow across a contact interface and into a gap region for nearby contact surfaces;
• are applicable when pore pressure degrees of freedom are present on both sides of a contact interface (if pore pressure degrees of freedom are present on only one side of a contact interface, the surfaces are treated as impermeable);
• affect the pore fluid flow normal to the contact surfaces;
• can apply to small- and finite-sliding contact formulations; and
• assume that there is no fluid flowing tangentially to the surface.
Contact in coupled pore fluid diffusion/stress analysis involves displacement constraints to resist penetrations and pore fluid contact properties that influence the fluid flow. See “Coupled pore fluid diffusion and stress analysis,” Section 6.8.1, for details on coupled pore fluid diffusion/stress analyses. See “Defining the constitutive response of fluid within the cohesive element gap,” Section 32.5.7, for details on the use of pore pressure cohesive elements as an alternative to using contact models and pore fluid contact properties.
Contact pressure in pore fluid interactions
The pore fluid contact properties discussed in this section apply when pore pressure degrees of freedom exist on both sides of a contact interface. In such cases the calculated contact pressure is effective; it does not include the pore fluid pressure contribution.
If only one side of a contact interface includes pore pressure degrees of freedom, no fluid flow into or across the contact interface occurs. In this case the reported contact pressure represents the total pressure, including the effective structural and pore fluid pressure contributions; but only the effective contact pressure is used for the computation of friction.
Including pore fluid properties in a contact property definition
Abaqus/Standard assumes that pore fluid flows in the normal direction at a contact interface and does not flow tangentially along the interface. Two contributions to the fluid flow into each surface at a contact interface are generally present, as shown in Figure 37.4.1–1. The fluid flow into the master and slave surface at corresponding points on the interface are q _ { S } and q _ { M } , respectively.
• One contribution ( q _ { a c r o s s } ) is associated with flow across the interface. A positive value of q _ { a c r o s s } corresponds to flow out from the master surface and into the slave surface.
• The other contribution ( q _ { g a p S } for the slave surface and q _ { g a p M } for the master surface) is associated with removing or adding fluid from the region between the surfaces while the gap distance is changing. The sign convention is such that q _ { g a p S } and q _ { g a p M } are positive when these contributions flow into the respective surfaces (while the gap width decreases). The sum of q _ { g a p S } and q _ { g a p M } (which is the same as the sum of q _ { S } and q _ { M } ) is equal to negative one times the rate of change of the gap width up to the threshold distance discussed in “Controlling the distance within which pore fluid contact properties are active.”
In steady-state analyses the rate of separation of the surfaces is zero, so the fluid flow contributions q _ { g a p S } and q _ { g a p M } are zero; all fluid flowing out of one surface flows into the other in steady-state analyses.
text_image
Slave surface qS1 = qgap S1 + qacross1 qM1 = qgap M1 - qacross1 d1 d2 Master surface
Figure 37.4.1–1 Flow patterns in the interface contact element.
Pore fluid flow at a contact interface typically occurs even if contact permeability characteristics are not explicitly specified in the contact property definition. Alternatively, you can directly specify contact permeability characteristics for enhanced control over the flow of fluid across a contact interface.
Input File Usage: *SURFACE INTERACTION, NAME=interaction_name *CONTACT PERMEABILITY
Controlling the distance within which pore fluid contact properties are active
The models governing fluid flow across a contact interface are most appropriate for two surfaces in contact or separated by a relatively small gap distance. By default, Abaqus assumes no fluid flow occurs once the surfaces have separated by a distance larger than the characteristic element length of the underlying surfaces. Alternatively, you can directly specify a cutoff gap distance beyond which no