- Friction Coefficient
Defines the value of the friction coefficient (unit less, available on the revolute, cylindrical, and translational joints)
- Radius
The value of the radius in the specified length unit. Used to compute resisting torque.
- Outer Radius
The value of the outer radius in the specified length unit. Used to compute the axial friction torque for a revolute joint.
- Effective Radius
The value of the effective radius in the specified length unit. Used to compute the torsional friction torque in a translational joint.
- Effective Length
The value of the effective length in the specified length unit. Used to compute the bending force and/or a bending torque.
The pictures below show the definition of geometric properties for joints in typical situations. The effect of normal force is shown by a red arrow.
- Cylindrical Joint
The typical situation for a cylindrical joint is a pin in a hole. A perfect joint (not gap between the pin and hole) is considered:
Tangential friction is due to radial forces (Fx and Fy) acting between the pin and the hole internal face. The tangential friction force leads to a resisting friction torque along the z-axis of the revolute. The friction torque is proportional to the tangential force via the pin radius.
The bending effect (reaction moment Mx and My) leads to two opposed forces. The effective length allows the program to compute the normal force from the moments Mx and My.
Note: The same definitions also apply to Revolute, Translational, and Point on Curve joints. In the Translational joint, the main axis is x and not z.
- Revolute Joint
A revolute joint is also a pin in a hole, but there are two flanges to prevent sliding on the sides. The axial force (along the revolute z-axis) leads to a resisting torque along the axis. An effective radius is used to convert the resisting force to the equivalent torque.
Another way to model a revolute joint is with a single flange on the pin between two side walls:
The computation of bending effect is similar to the cylindrical joint except that the effective length is given by the distance between the two walls:
The axial effect is due to contact between the flange and the wall:
- Translational Joint
Translational joints typically have a rectangular cross-section. An equivalent effective radius is used to simplify the computation of the torsion effect (moment along translational x-axis).
- Point on Curve Joint
Point on Curve joints are similar to translational joints.
- Spherical Joint
The typical situation for a spherical joint is a ball and socket.
- Slot Joint
Slot joints are similar to both translational and spherical joints.
- Universal Joint
Universal joints enable two rotations along x and z axis.
- In-Plane, Spherical, and Radial Gap Joints
- General Joint
Friction is allowed in general joints in the following cases:
The joint has a single translational degree of freedom and/or a single rotation degree of freedom. In this case, the joint is similar to a translational, revolute or cylindrical joint.
The joint has a single translational degree of freedom and/or its rotations are all free. In this case the joint is similar to a slot or spherical joint.
For more information, see Material Behavior of Joint Elements.