week-11 Joint creation and Demonstration

AIM
Using the LS DYNA manual (*CONSTRAINED_JOINT keyword) demonstrate spherical, revolute, cylindrical, and translational joints between two rigid bodies and two deformable bodies.

A Mechanical joint is a section of a machine that is used to connect one or more mechanical parts to another. Mechanical joints may be temporary or permanent, most types are designed to be disassembled. Most mechanical joints are designed to allow relative movement of these mechanical parts of the machine in one degree freedom and restrict movement in one or more others.

Types of joints:

1. Mechanical joints are broadly classified into two classes non-permanent and permanent joints.

2. Non-permanent joints can be assembled and dissembled with out damaging the components.

3. Examples of such joints are threaded fasteners (like screw-joints), keys and couplings etc.,

4. permanent joints cannot be dissembled without damaging the components. These joints can be of two kinds depending upon the nature of the force that holds the two parts.

5. The force can be of mechanical origin, for example, riveted joints, joints formed by press or interference fit where two components are joined by applying mechanical force.

6. The components can also be joined by molecular force, for example, welded joints,brazed joints, joints with adhesives etc,

Here are the principles of revolute,cylindircal,spherical and translational joints between two rigid and deformable bodies are demonstrated.

PROCEDURE

1.Revolute Joint:

A revolut joints(also called pin joint or hinge joint) is one degree of freedom kinectic pair used frequently in mechanisms and machines. The joint constrains the motion of two bodies to pure rotation along a common axis. The joint doesnot allow translation or sliding linear motion, a constraint not shown in the diagram. Almost all assemblies of multiple moving bodies include revolute joints in their designs. Revolut joints are used in numerous applications such as door hinges, mechanisms and other uni-axial rotational devices.

Revolute Joint. Nodes 1 and 2 are coincident; nodes 3 and 4 are coincident. Nodes 1 and 3 belong to rigid body A; nodes 2 and 4 belong to rigid body B. The relative motion of the two rigid bodies is restricted to rotations about the axis formed by the two pairs of coincident nodes. This axis is labeled the "centerline."

CASE 1:

Revolute joint between Rigid bodies:

1. Create two 4-noded shell using mesh>shape mesher>4 noded shell and enter coordinates in P1,P2,P3,P4.

2. Assign 1 shell component as part 1 and another one as part-2

Create two nodes in between shell and capture their ID's.

Create Another two nodes which coincide with the other two nodes.

Create a Node ser consisting of nodes 18land 182 and another node set consisting of 183 and 184. Create a section for the shell components with Eleform = 2 and give thickenss

MAT_RIGID card is assigned with the properties of steel

Part Creation

Assign the section and material to the 2 parts created.

CONSTRAINED_EXTRA_NODES:

1.The node set ID which contains nodes 181,182 is considered as fixed nodes assigned to the part-1 which is also fixed.

2. The node set ID which contains nodes 183,184 which in coincided with 181 and 182 is considered as moving nodes is assigned to part 2

Constrained_joint_revolute:

1. Constrained joint revolute is defined and the nodes which are coinciding are entered.

Displacement:

1. Displacement is given to A node in anyone of the parts by defining displacement curve, here displacement is given to a node belongs to part-2

BOUNDARY SPC SET AND PRESCRIBED MOTION SET:

CONTROL CARDS:
1. Control cards such as control termination, control implicit auto,control implicit general, and control time step is defined

2. As displacement is given implicit solver is chosen for better results

DATABASE binary D3plot

RESULTS:

CASE2: Revolute joints between two deformable bodies:

1. For deformable bodies the constrained extra nodes is replaced with constrained _nodal_rigid_body

2. Mat elastic is defined instead of rigid

Procedure

1. Create 4 nodes in the middle individually which is initially nor coincided with each other.

Create nodal rigid body from part 1 and 2 considering the 4 nodes

RESULT:

SPHERICAL JOINTS:

Spherical joint. The relative motion of the rigid bodies is constrained so that nodes which are initially coincident remain coincident. In the above figure the socket's node is not interior to the socket-LS-DYNA does not require that a rigid body's nodes be interior to the body.

CASE 1: Spherical joint between rigid bodies:

1. Create 2 shell sphere by mesh>shape mesher>sphere shell

2. Create 2 shell sphere with 2 different radius and one sphere is trimmed half.

3. Create 2 nodes at the center and assign each node to belong to each part individually.

Constrained Extra node:

Constrained Spherical Joint:

MATERIAL:

INITIAL VELOCITY RIGID BODY:

The Outer Sphere is constrained in all DOF's

CONTROL TERMINATION AND TIMESTEP CARDS ARE ASSIGNED and all other keywords are same as the previous one.

SPHERICAL DEFORMABLE:

CYLINDRICAL JOINT

A cylindrical joint is two degrees of freedom kinectic pari used in mechanisms. Cylindrical joints provide a single-axis sliding function as well as a single axis rotation, providing a way for two rigid bodies to translate and rotate freely. This can be pictured by unsecured axle mounted on a chassis, as it may freely rotate and translate.

Cylindrical Joint. This joint is derived from the rotational joint by relaxing the constraints along the centerline. This joint admits relative rotation and translation along the centerline.

CASE 1 CYLNDRICAL RIGID

Create 2 cylindrical sphere by mesh>shape mesher>cylinder shell

Create 2 cylinder shell with 2 different lenghts and radius.

Two cylinders were created with the radius of 20 and 22 mm of different lengths Procedure:
Create 2 nodes at the centre and node set is create with these nodes and assigned to part 1 create other 2 nodes at centre and node set is created with these nodes and assigned to part 2.

CONSTRAINED EXTRA NODE SET

CONSTRAINED JOINT CYLINDRICAL:

MATERIAL RIGID:

INITIAL VELOCITY RIGID BODY:

BOUNDARY SPEC SET:

CASE 2: CYLINDE BETWEEEN DEFORMABLE BODIES:

MATERIAL:

INITIAL VELOCITY

TRANSLATIONAL JOINTS:
A Translational joint allows one part to translate along a vector in respect of another part. The parts can only translate, not rotate, in respect of each other. The joint has one traslational degree of freedom, and the rotational degree of freedom is 0.

Translational joint. This is a cylindrical joint with a third pair of off-centerline nodes which restrict rotation. Aside from translation along the centerline, the two rigid bodies are stuck together.

CASE1. TRANSLATIONAL JOINT BETWEEN RIGID:

1. Create 2 shell boxes of different heights and length using shape mesher option.

PROCEDURE:
1. Create 2 nodes at the centre and a node at the centre between these 2 nodes slightly deviated from axis of the 2 nodes and a node sets are created and assigned to the repsective part 1 and 2

CONSTRAINED NODES AND JOINT

MATERIAL

BOUNDARY SPEC SET

DEFORMABLE BODIES :

MATERIAL

CONSTRAINED NODAL RIGID BODY

INITIAL VELOCITY

CONCLUSION:

All the joints,spherical revolute,cylindrical and translational between rigid and deformable bodies are demonstrated with the help of LS-DYNA manual.