Joint creation and Demonstration using LS-Dyna

OBJECTIVE:

To demonstrate spherical, revolute, spherical, and translational joints between two deformable bodies and two rigid bodies. The following objectives have to be satisfied.

1. The gif file has to be compiled for all the joints.

2.  *CONSTRAINED_EXTRA_NODES and *CONSTRAINED_NODAL_RIGID_BODY are to be used to create joints between rigid and deformable bodies respectively. 

PROCEDURE:

For creating joints between rigid bodies:

• Revolute Joint:

1. Open LS-PrePost. Go to Mesh>>Shape Mesh>>Entity: 4N Shell>> Create two Parts as shown in the figure below.

    

2. Go to Keyword Manager>>Name the created parts with a suitable name

3. The material and section card has to be defined and assigned to the part. The two cards are shown in the figure below.

4. Go to Element Tools>>Node Edit>>Create>>Four nodes have to be created at the center of the two plates. Two pairs of created nodes are to be defined using *SET NODE in the Create Entity option. A pair of nodes have to be assigned to the part using *CONSTRAINED_EXTRA_NODES. This is shown in the figure below.

  

  

  

 

5. For applying boundary conditions, the following nodes (highlighted in green) shown in the figure has to be fixed.

  

The nodes highlighted in green color has to be arrested in all DOF's

6. The revolute joint is defined using *CONSTRAINED_JOINT_REVOLUTE

The nodes N1 and N3 must be in rigid body A. The nodes N2 and N4 must be in rigid body B.

7. For defining displacement, the node highlighted in red has to be selected. 

  

   

8. The displacement curve ID is shown in the figure below.

9. The *CONTROL_TIMESTEP card has to be defined using the LCTM option. The load curve ID is shown in the figure below. The total termination time is defined as 5ms.

10. The file is saved with a suitable name with .k extension. The file is ran using LS-Dyna Manager.

• Cylindrical Joint:

1. Open LS-PrePost. Go to Mesh>>Shape Mesh>>Entity: Cylinder Shell>> Create two Parts as shown in the figure below. The parts are named appropriately using the keyword manager.

            

2. Follow steps 3 and 4 as given in the revolute joint. The images are shown below.

               

             

3. The cylindrical joint is defined using the keyword *CONSTRAINED_JOINT_CYLINDRICAL

     

The nodes N1 and N3 must be in rigid body A. The nodes N2 and N4 must be in rigid body B.

4. The velocity is defined using the keyword *INITIAL_VELOCITY_RIGID_BODY. This is shown in the figure below.

    

5. Follow steps 9 and 10 as given in the revolute joint.

• Spherical Joint:

1. Open LS-PrePost. Go to Mesh>>Shape Mesh>>Entity: Sphere Shell>> Create two Parts as shown in the figure below. Half of the outer spherical shell is deleted. The parts are named appropriately using the keyword manager.

                                        

2. Follow steps 3 and 4 as given in the revolute joint. The images are shown below.

                                     

                                             

3. The cylindrical joint is defined using the keyword *CONSTRAINED_JOINT_SPHERICAL

      

The nodes N1 and N2 must be in rigid bodies A and B respectively. 

4. The velocity is defined using the keyword *INITIAL_VELOCITY_RIGID_BODY. This is shown in the figure below.

    

5. Follow steps 9 and 10 as given in the revolute joint.

• Translational Joint:

1. Open LS-PrePost. Go to Mesh>>Shape Mesh>>Entity: 4N Shell>> Create a face>>Go to Element Generation>>Shell>>Edge Drag. Select the edges of the face and drag it along an axis. The final geometry obtained is shown in the figure below. Half of the outer spherical shell is deleted. The parts are named appropriately using the keyword manager.

                            

2. Repeat step 2 as given in the revolute joint.

3. For this joint, three pairs of nodes have to be defined. Two pairs of nodes must be coincident and collinear. The third pair of nodes must be in between the other two pairs and slightly displaced from the axis of the other pair of nodes. This is shown in the figure below.

                  

                       

As shown in the figure above, the nodes have to be assigned to the respective part. The nodes highlighted in red and blue indicates the part to which it belongs to.

4. The cylindrical joint is defined using the keyword *CONSTRAINED_JOINT_TRANSLATIONAL

      

The nodes N1, N3, and N5 must be in rigid body A and nodes N2, N4 and N6 must be in rigid body B. 

5. The velocity is defined using the keyword *INITIAL_VELOCITY_RIGID_BODY. This is shown in the figure below.

    

6. Follow steps 9 and 10 as given in the revolute joint.

For creating joints between deformable bodies:

• Revolute Joint:

1. Repeat step 1 of the revolute joint of rigid bodies. Rename the created parts using the keyword Manager.

2. The section card is the same as the joint creation in rigid bodies. The material card is shown in the figure below.

       

3. Repeat step 4 of the revolute joint of rigid bodies. After this step go to Create Entity>>Constrained>>CNRB. In this option uncheck Create P-Node option and select the generated node and nodes on the body. Create a CNRB as shown in the figure below. Only CNRB nodes has to be created. *CONSTRAINED_EXTRA_NODES should not be used.

      

4. The revolute joint is defined using *CONSTRAINED_JOINT_REVOLUTE

The nodes N1 and N3 must be in rigid body A. The nodes N2 and N4 must be in rigid body B.

5. Repeat the steps 5-10 as that of revolute joint of rigid bodies.

• Cylindrical Joint:

1. Follow step 1 as that of cylindrical joint for deformable bodies.

2. The material card is shown in the figure below. The section card remains the same for the two cases.

        

3. Create extra nodes as given in the case of revolute joint of deformbale bodies and repeat step 3 of the revolute joint of deformable bodies as given above. Only CNRB nodes has to be created. *CONSTRAINED_EXTRA_NODES should not be used.

                              

3. The cylindrical joint is defined using the keyword *CONSTRAINED_JOINT_CYLINDRICAL

     

The nodes N1 and N3 must be in rigid body A. The nodes N2 and N4 must be in rigid body B.

4. The velocity is defined using the keyword *INITIAL_VELOCITY. This is shown in the figure below.

                 

The nodeset ID corresponds to the moving cylinder part.

5. The run time and control cards remains the same for the two cases.

• Spherical Joint:

1. Repeat the steps 1 and 2 as given in the spherical joint for rigid bodies. The material and section cards remains the same as the previous joint between deformable bodies.

2. Create the CNRB nodes as shown in the figure below. Only CNRB nodes has to be created. *CONSTRAINED_EXTRA_NODES should not be used.

           

3. The spherical joint is defined using the keyword *CONSTRAINED_JOINT_SPHERICAL

     

The nodes N1 and N2 must be in rigid body A and B respectivley. 

4. The velocity is defined using the keyword *INITIAL_VELOCITY. This is shown in the figure below.

                           

The nodeset ID corresponds to the rotating sphere part.

5. The run time and control cards remains the same for the two cases.

• Translational Joint:

1. Repeat the steps 1-3 as given in the joint definition of translational joint between rigid bodies. The material and section cards remains the same as the previous cases of joint between deformable bodies.

2. Create the CNRB nodes as shown in the figure below. Only CNRB nodes has to be created. *CONSTRAINED_EXTRA_NODES should not be used.

  

                    

The joint defintion remains the same but the way of implementation differs.

3. The translational joint is defined using the keyword *CONSTRAINED_JOINT_TRANSLATIONAL

     

The nodes N1, N3, and N5 must be in rigid body A and the nodes N2, N4, and N6 must be in rigid body B.

4. The velocity is defined using the keyword *INITIAL_VELOCITY. This is shown in the figure below.

                                 

The nodeset ID corresponds to the moving part.

5. The run time and control cards remains the same for the two cases.

RESULTS AND CONCLUSION:

Joints between rigid bodies:

• Revolute Joint:

• Cylindrical Joint:

• Spherical Joint:

• Translational Joint:

Joints between deformable bodies:

• Revolute Joint:

• Cylindrical Joint:

• Spherical Joint:

• Translational Joint:

NOTE:

1. The simulation run time for joints between deformable bodies is more than the rigid bodies. This is due to the calculation of stress and strain values in the case of deformable bodies.

2. The definition of joints for the two cases remains the same. The way of implementation differs.

3. If we use the elastic material card and define the joints using *CONSTRAINT_EXTRA_NODES we will get an error.

4. There are two methods adopted because of the solver limitation and capabilities.

CONCLUSION:

Therefore, all the given joints are modeled for rigid and deformable bodies. All the objectives are satisfied. The following points were learned from this challenge.

1. Revolute Joint: These are defined by two pair of nodes which are coincident to each other. Only a rotational degree of freedom is possible along the axis of nodes.

2. Cylindrical Joint: These are defined by two pairs of nodes that are coincident along the center axis of two bodies. In this joint rotation and translation is possible along the defined axis.

3. Spherical Joint: This is defined by a pair of nodes. Only a rotational degree of freedom is possible for this type of joint.

4. Translational Joint: These are defined by three pairs of nodes. The third pair of nodes is offset from the center axis nodes which restricts the rotational degree of freedom. Only a translational degree of freedom is possible along the defined axis.

Drive Link:https://drive.google.com/file/d/1dJAZ84cXdWp9EQcYDX4LbTE0QtrY6Mp2/view?usp=sharing