7.2. Modeling Electric Contact

You can use surface-to-surface contact elements or the node-to-surface contact element, in combination with thermal-electric elements and solid coupled field elements to model electric current conduction. You can also use surface-to-surface contact elements, in combination with piezoelectric and electrostatic elements, to model electric charge across a contacting interface.

KEYOPT(1) provides degree of freedom options for modeling electric contact. For combined structural/thermal/electric contact, set KEYOPT(1) = 3 to activate the structural, thermal, and electric current DOFs. For pure thermal/electric contact, set KEYOPT(1) = 4 to activate the thermal and electric current DOFs. For piezoelectric contact, set KEYOPT(1) = 5 to activate the structural and piezoelectric DOFs. For electrostatic contact, set KEYOPT(1) = 6 to activate the electrostatic DOF.

The electric contact features are:

7.2.1. Modeling Surface Interaction

7.2.1.1. Background

To take into account the surface interaction for electric contact, you need to specify the electric contact conductance per unit area if you are using the electric current degree of freedom, or the electric contact capacitance per unit area if you are using the piezoelectric or electrostatic degrees of freedom. For either case, this parameter is ECC. You specify ECC through a real constant table. You can use a tabular input to define ECC as a function of contact pressure (pressure as a table), average temperature on contact detection point (temperature as a table), and time. If the “bonded contact” or “no-separation contact” option is set, contact interaction can occur between two surfaces separated by a narrow gap.

7.2.1.2. Using ECC

The interaction between two contacting surfaces is defined by

J = ECC x (Vt - Vc)

where:

J = current density for the electric potential (VOLT) degree of freedom (KEYOPT(1) = 3 or 4), or the electric charge density (KEYOPT(1) = 5, or 6).
ECC = electric contact conductance for the electric potential (VOLT) degree of freedom (KEYOPT(1) = 3 or 4), or the electric contact capacitance per unit area for (KEYOPT(1) = 5, or 6).
Vt and Vc = voltages at the contact points on the target and contact surfaces.

The ECC value is input through a real constant, which can be a function of temperature [(Tt + Tc)/2], pressure, and time, by using the %TABLE% option. For the current conduction option, the electric contact conductance ECC has units of electric conductivity/length. For the piezoelectric and electrostatic options, the electric contact capacitance ECC has units of capacitance per unit area. To model surface interaction between two surfaces where a small gap exists, use KEYOPT(12) = 4 or 5 to define either the “bonded contact” or “no-separation contact” options (see Selecting Surface Interaction Models).


Note:

For force-based node-to-surface contact, ECC has units of (electric conductivity)*(LENGTH) or the capacitance.

7.2.2. Modeling Heat Generation Due to Electric Current

For electric current field analyses (KEYOPT(1) = 3 or 4), the heat generation due to electric current is given by

q = FHEG x J x (VT - VC)

Where

FHEG: The fraction of electric dissipated energy converted into heat (Joule heating). This value defaults to 1 and can be input as a real constant. For an input of true 0, you must enter a very small value (for example, 1E-8). If you enter 0, ANSYS interprets this as an input of the default value.
J: The current density.
Vt and Vc: The voltages at the contact points on the target and contact surfaces.

The amount of electric heat dissipation on contact and target surfaces is defined by

qc = FWGT x q

and

qT = (1 - FWGT) x q

Where qc is the contact side and qT is the target side, and FWGT is the weight factor for the contact heat dissipation between the contact and target surfaces (input as a real constant). FWGT is the same real constant used for frictional heat generation. By default, FWGT = 0.5. For an input of true 0, you must enter a very small value (for example, 1E-8). If you enter 0, ANSYS interprets this as an input of the default value.


Release 14.0 - © 2011 SAS IP, Inc. All rights reserved.