Beam Properties: Point Contact

Description

Used for the definition of point contact properties.

Common Toolbar

See Properties: Common Controls.

Properties Tab

Type

Type of contact behaviour.

Zero Gap

Provides stiffness only in compression, activating only when the gap between the two nodes is closed.

Supports friction.
Normal Gap

Provides stiffness only in compression, activating as soon as it is compressed.

The initial length of the element is defined by the physical length in the model as well as any applied pre-strain attributes. These attributes can be used to change the activation point on the element.

Supports friction.
Tension Gap

Similar to normal gap, except it also carries tension up to a the value specified as Maximum Tension.

Does not support friction.
Takeup Gap

Allows for ratcheting type action between two nodes; this ratcheting action can be set to act in either tension or compression, based on the Takeup Action setting.

Does not support friction.

Dynamic Axial Stiffness

If set, allows the solver to increase or decrease the axial stiffness to better enforce the contact condition. Stiffness is scaled until the target penetration value in an active element (i.e., the Strain Tolerance), is reached. The stiffness used in the analysis when this option is set, is listed in the solver log file at the end of each load step.

If not set, the stiffness does not change throughout the analysis.

Applies only to Zero Gap and Normal Gap contact elements.

Update direction

If set, the direction of the contact element is updated in geometric nonlinear analysis based on the displacements.

If not set, the direction of the element is not updated and contact forces always act in the original direction of the element axis. To establish whether the element is in contact or not in geometric nonlinear analysis, the gap is measured based on the projection of the node displacements onto the original axial direction vector of the element.

Friction Model

Specifies the friction model used by the contact element when non-zero coefficients of friction are set.

Elastic

Friction forces do not return to zero until relative displacement is also zero; they traverse the same path in reverse when frictional movement is reversed. Frictional hysteresis cannot be observed with this model.
Plastic

Frictional forces return to zero and change sign when frictional movement is reversed, provided the small elasticity of the element, as determined by the friction stiffness, has been overcome. Frictional hysteresis can be observed with this model.

Yield Surface

Specifies the yield surface used by the friction model.

Rectangular

Frictional forces are considered independently of each other in the two principal directions of the element. In each direction, the maximum frictional force V_i is the axial force F times the friction coefficient. This defines a rectangular yield surface where
Elliptical

Frictional forces in the two principal directions are considered in a coupled manner. The two frictional force components are always on an ellipse such that

Takeup Action

Specifies the direction of movement that is resisted by Takeup gap type elements.

Tension

Relative motion in the tensile direction is not allowed (i.e., it is resisted), while relative motion in the compressive direction can occur freely.
Compression

Relative motion in the compressive direction is not allowed (i.e., it is resisted), while relative motion in the tensile direction can occur freely.

Friction Coefficients (C1 / C2)

Friction coefficients in the principal 1 and 2 axis directions.

Apply only to Zero Gap and Normal Gap type elements.

Maximum Tension

Maximum tensile force that can be resisted by Tension Gap type elements.

Initial Axial Stiffness / Axial Stiffness

Stiffness used for the contact element.

If Dynamic Stiffness is set, this specifies the initial axial stiffness, allowing the solver to scale the stiffness up or down to satisfy the Strain Tolerance condition.

If Dynamic Stiffness is not set, this specifies the stiffness used by the element whenever it is active, irrespective of how much it has compressed.

Lateral Stiffness / Sticking Friction Stiffness

For the Tension Gap, the Lateral Stiffness defines a constant value of lateral stiffness to be added while the element is active.

For Zero Gap and Normal Gap elements with non-zero coefficients of friction, the Sticking Friction Stiffness provides the lateral elastic connection between nodes until the point where the element slips in the lateral (frictional) direction; while the frictional force is below the current frictional capacity the lateral elastic stiffness is added. Because the lateral connection between nodes is via a prescribed stiffness, there will always be some lateral relative movement in the element even though the element has not yet slipped. The amount of pre-slip relative lateral movement can be controlled by adjusting the stiffness value.

Strain Tolerance

This value defines a tolerance for active point contacts. If the Dynamic Axial Stiffness option is set, the axial stiffness of an active point contact will be continually scaled so that its axial compressive strain is no greater than the Strain Tolerance value. If the Dynamic Axial Stiffness option is not set, the axial stiffness of a point contact will be equal to the defined Axial Stiffness when the axial compressive strain reaches or exceeds the Strain Tolerance value; it will be reduced towards zero as the axial strain approaches zero. Note that “zero stiffness” is defined as Axial Stiffness times the Point contact zero stiffness factor (0 to 1) specified in the solver parameters.

Common