Mechanical Joints in LS-Dyna for Explicit Analysis
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This document discusses different types of mechanical joints that can be modeled in LS-Dyna explicit analysis, including spherical, revolute, planar, and gear joints. It provides introductions and definitions for each joint type, along with examples of their motions and how they are defined using LS-Dyna keywords. Videos are included showing examples of each joint type in action under simulated loading conditions.
Mechanical Joints in LS-Dyna for Explicit Analysis
- 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
- 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.
- 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