This describes steps to define various useful mechanical joints in LS-Dyna along with their motion.

1. MECHANICAL JOINTS IN LS-
DYNA EXPLICIT ANALYSIS
AKSHAY MISTRI
WAYNE STATE UNIVERSITY, DETROIT, MI
NOTES ON JOINTS CREATION

2. TYPES OF JOINTS
I. Spherical Joint
I. Introduction & Definition
II. Relative Penalty Stiffness
II. Revolute Joint
I. Introduction
II. Definition
III. Motion
III.Planar Joint
I. Introduction
II. Definition
III. Motion
IV. Gear Joint
I. Introduction
II. Definition
III. Motion

3. SPHERICAL JOINT

4. SPHERICAL JOINT – INTRODUCTION &
DEFINITION
• Practical applications:
• Connection between wheel knuckle and suspension arms.
• Shoulder joint is a spherical joint.
• Consider the joint to exist between the blue tube and the red plate.
• Note:
• Two coincident nodes needed to create a joint.
• The two nodes must belong to two rigid bodies between which joints needs to be
established.
• If the two nodes cannot be coincident between the two bodies:
• Then create two coincident nodes joint location.
• Assign each node to a rigid body via *CONSTRAINED_EXTRA_NODE/SET.
• The yellow cube with elastic material is included to avoid timestep issues only.

5. RELATIVE PENALTY STIFFNESS EFFECT
RPS : 1
https://youtu.be/aSeuyXB_gu
A
RPS : 10
https://youtu.be/BWAvUP_byek
RPS : 100
https://youtu.be/n7Ke65zAk-A
With increase of penalty stiffness, relative motion between the two nodes of the joint reduces.

6. REVOLUTE JOINT

7. REVOLUTE JOINT - INTRODUCTION
• Practical applications:
• Connection between bicycle body and steering handlebars.
• Door hinges.
• Consider the joint to exist between the blue fixed plate and the red plate, free to
rotate around the center of the blue plate.
• Note:
• Four nodes are needed to define the joint, two from rigid body A and two from B.
• Also, the two node pairs from the rigid bodies must be coincident.
Source: LS-Dyna Keyword Manual

8. REVOLUTE JOINT - DEFINITION
• For joint definition we would need two pair of coincident nodes.
• Hence, the two yellow nodes are defined which are coincident to the two nodes in the
red plate.
• Now the two yellow nodes are constrained to the blue plate with
*CONSTRAINED_EXTRA_NODES_SET option.
• Now, joint can be defined using *CONSTRAINED_JOINT_REVOLUTE.
• Now gravity can be applied to the system in negative y direction to check the revolute
joint in action.
• This can be done using *LOAD_BODY_Y, which would need a curve with time on x-
axis (0 to the time simulation runs) and gravity constant on y axis.
• Curve can be defined using *DEFINE_CURVE.
• Some mass can be added to the free end of the red plate.

9. REVOLUTE JOINT - MOTION
https://youtu.be/L6E6zShcpGw

10. PLANAR JOINT

11. PLANAR JOINT - INTRODUCTION
• Constraints motion of a rigid body in a plane.
• Practical applications:
• Motion on a conveyer belt.
• Motion of a piston in the engine block.
• Consider the joint to exist b/w the red fixed plate and blue slider.
• Gravity to exist in x – direction.
• Blue slider will slide on the red plate due to gravity acting in x-direction.

12. PLANAR JOINT - DEFINITION
• For joint definition we would need two pair of coincident nodes, similar to revolute joint.
• Hence, the two nodes pairs 1280, 1500 and 1224, 1501 are coincidental. Nodes 1280 and 1224 belong to slider.
• Nodes 1500 and 1501 are created on exactly same locations as of 1280 and 1224 and are constrained to the red plate with
*CONSTRAINED_EXTRA_NODES_SET option.
• Now, joint can be defined using *CONSTRAINED_JOINT_REVOLUTE.
• Gravity can be applied to the system in x direction to check the planar joint in action.
• This can be done using *LOAD_BODY_X, which would need a curve with time on x-axis (0 to the time simulation runs) and
gravity constant on y axis.
• Curve can be defined using *DEFINE_CURVE.
1224, 1501
1280, 1500

13. PLANAR JOINT - MOTION
https://youtu.be/3iFs50_q2zc

14. GEAR JOINT

15. GEAR JOINT - INTRODUCTION
• Gear joint is used to reverse, change rotational speed or axis of rotation.
• Practical applications:
• Power transmission from engine to wheels.
• Steering rack mechanism.
• Consider the red component as the gear and the blue as pinion.

16. GEAR JOINT - DEFINITION
• It can be defined by *CONTRAINED_JOINT_GEARS.
• Node pairs 1, 3 and 737, 4 define the gear and pinion axes.
• Node 1, 5 and 737, 765 define the gear plane.
• Node 3 and 4 are constrained by *CONSTRAINED_EXTRA_NODES to the red and blue rigid body components.
• PARM defines the gear ratio.
• Gear rotation is induced by using *BOUNDARY_PRESCRIBED_MOTION_RIGID. LCID refers to a curve defining time vs
rotational velocity of the gear.

17. GEAR JOINT - MOTION
https://youtu.be/CAYFT_JUowc