week-11 Joint creation and Demonstration

Objective:

To create Cylindrical,Translational,Revolute & Spherical joints between two Rigid and two deformable bodies using Ls-Dyna solver.

Theory:

A Mechanical joint is a section of a Machine that is used to connect one or more mechanical parts to another. A mechanical joints may be permanent or temporary 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 of freedom , and restrict movement in one or more others.

• Temporary joints can be assembled and dissembled without damaging the components. Eg. thread fastners, keys, couplings etc.,
• Permanent Joints are the ones which cannot be dissembled without damaging the component, these joints are of two types depending on the nature of the force that holds the two parts
• The forces can be of mechanical origin where two components are joined by applying mechanical force Eg. Riveted joints
• The components can also be joined by molecular force Eg. welded joints

Procedure:

• Here we need to create four joints, i.e., Cylindrical,Translational,Revolute & Spherical joints
• The joints which are to be created is between two rigid bodies and two deformable bodies separately which are considered as two cases here

Case setup & Execution:

Some Common cards used through out:

Since we are studying only about the characteristics of the joints, there are some cards which is common in all the cases which are as Follows

1: Section:

the section shell card with Element formulation of 2 and thickness of 2mm is Followed through out to all the cases for both rigids and deformables.

2. Material card:

the material card *MAT_RIGID is used for all the rigid cases in all four joints with the properties of steel given.

the material card *MAT_ELASTIC is used for all the deformable cases in all four joints with the properties of aluminium is given

3. Control cards:

The control cards such as *Control_Termination and *Control_Timestep is common through out all the cases in all the four joints.

In *Database_Binary_D3Plot the DT is given as 0.01

1. Revloute joints:

A revolute joint (also called pin joint or hinge joint) is a one degree of freedom kinematic pair used frequently in mechanisms and machines.The joint constrains the motion of two bodies to pure rotation along a common axis. The joint does not 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. Revolute joints are used in numerous applications such as door hinges, mechanisms, and other uni-axial rotation devices.

A revolute joint is usually made by a pin or knuckle joint, through a rotary bearing. It enforces a cylindrical contact area, which makes it a lower kinematic pair also called a full joint. However, If there is any clearance between the pin and hole (as there must be for motion), so-called surface contact in the pin joint actually becomes line contact.

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(i): Rigids

1. Two 4-noded Shell is created using the mesh option with two part Id's

2. Four nodes should be created with two pair of coincident nodes at the centre between the two shell elemets parts which is created. i.e., here nodes 129 and 131 are coinciding and nodes 130 and 132 are coinciding.

3. To assign the nodes to their parts we first need to create Node set containing the pairs which are needed to be assigned, then using the key word *CONSTRAINED_EXTRA_NODES_SET

The Node set containing nodes 129 and 130 is assigned to Part 1

The Node Set containing node 131 and 132 is assigned to Part 2

4. The coincident nodes are enetered in the Card *CONSTRAINED_JOINT_REVOLUTE

After this Velocity Rigid is given to Part 2 while part 1 is fixed using Spc

Results:

Case(ii): Deformable

1. For Deformable we need to create CNRB in place of *CONSTRAINED_EXTRA_NODES_SET

2. As mentioned above the material card is changed from Mat_rigid to Mat_Elas

3. Also the velocity_rigid card is changed to Initial velocity since we are not using any Rigids here

4. All other cards are similar to the above

Results:

2. Spherical Joints:

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(i): Rigids:

1. Two Spherical shell is created using the mesh option with two part Id's

2. Two nodes is created at the centre of the spheres coincident to each other.

3. To assign the nodes to their parts we first need to create Node set containing the nodes which are needed to be assigned, then using the key word *CONSTRAINED_EXTRA_NODES_SET

The Node set containing nodes 305 is assigned to Part 1

The Node Set containing node 306 is assigned to Part 2

4. The coincident nodes are enetered in the Card *CONSTRAINED_JOINT_SPHERICAL

After this A rotational Velocity Rigid is given to Part 1 while part 2 is fixed using Spc

Results:

Case(ii): Deformable

1. For Deformable we need to create CNRB in place of *CONSTRAINED_EXTRA_NODES_SET

2. As mentioned above the material card is changed from Mat_rigid to Mat_Elas

3. Also the velocity_rigid card is changed to Initial velocity since we are not using any Rigids here

4. All other cards are similar to the above

Results:

3. Cylindrical Joints:

A cylindrical joint is a two-degrees of freedom kinematic pair used in mechanisms. Cylindrical joints provide 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 an unsecured axle mounted on a chassis, as it may freely rotate and translate. An example of this would be the rotating rods of a table football.

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(i): Rigids:

1. Two Cylindrical shell is created using the mesh option with two part Id's

2. Four nodes should be created with two pair of coincident nodes at the centre axis of the two shell elemets parts which is created. i.e., here nodes 363 and 368 are coinciding and nodes 366 and 367 are coinciding.

3. To assign the nodes to their parts we first need to create Node set containing the pairs which are needed to be assigned, then using the key word *CONSTRAINED_EXTRA_NODES_SET

The Node set containing nodes 363 and 366 is assigned to Part 1

The Node Set containing node 368 and 367 is assigned to Part 2

4. The coincident nodes are enetered in the Card *CONSTRAINED_JOINT_CYLINDRICAL

After this Velocity Rigid is given to Part 2 while part 1 is fixed using Spc

Results:

Case(ii): Deformable

1. For Deformable we need to create CNRB in place of *CONSTRAINED_EXTRA_NODES_SET

2. As mentioned above the material card is changed from Mat_rigid to Mat_Elas

3. Also the velocity_rigid card is changed to Initial velocity since we are not using any Rigids here

4. All other cards are similar to the above

Results:

4. 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. This joint has one translational degree of freedom, and the rotational degree of freedom is 0. An axis of the translation is the z-axis.

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.

Case(i): Rigids:

1. Two Cylindrical shell is created using the mesh option with two part Id's

2. Six nodes should be created with three pair of coincident nodes at the centre axis of the two shell elemets parts which is created. i.e., here nodes 2500 and 2503 are coinciding , nodes 2501 and 2504 are coinciding and nodes 2502 and 2505 are coinciding.

3. To assign the nodes to their parts we first need to create Node set containing the pairs which are needed to be assigned, then using the key word *CONSTRAINED_EXTRA_NODES_SET

The Node set containing nodes 2500, 2501 and 2502 is assigned to Part 1

The Node Set containing node 2503, 2504 and 2505 is assigned to Part 2

4. The coincident nodes are enetered in the Card *CONSTRAINED_JOINT_TRANSLATIONAL

After this Velocity Rigid is given to Part 2 while part 1 is fixed using Spc

Results:

Case(ii): Deformable

1. For Deformable we need to create CNRB in place of *CONSTRAINED_EXTRA_NODES_SET

2. As mentioned above the material card is changed from Mat_rigid to Mat_Elas

3. Also the velocity_rigid card is changed to Initial velocity since we are not using any Rigids here

4. All other cards are similar to the above

Results:

Conclusion:

The Cylindrical,Translational,Revolute & Spherical joints between two Rigid and two deformable bodies are created using Ls-Dyna solver with the help of "ls-dyna_manual_volume_i_r12" .