week-11 Joint creation and Demonstration

JOINT CREATION AND DEMONSTRATION IN LS-DYNA

AIM

To demonstrate spherical, revolute, cylindrical, and translational joints between two rigid bodies and two deformable bodies. 

THEORY

A distinguishing feature of multibody systems is the presence of joints that impose constraints on the relative motion of the various bodies of the system. Most joints used in practical applications can be modelled in terms of the so-called lower pairs like spherical, revolute, cylindrical, and translational joints

Spherical Joint: A spherical joint is used for allowing free rotation in two planes at the same time while preventing translation in any direction, including rotating in those planes.

Fig.1 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.

Revolute Joint: A revolute 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.

Fig.2 Revolute Joint.

As shown in fig.2, 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 labelled the “centerline”.

Cylindrical Joint: A cylindrical joint is a two degrees of freedom kinematic pair used in mechanisms. It provides single axis sliding function as well as a single axis rotation, providing a way for two rigid bodies to translate and rotate freely.

Fig.3 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 as shown in fig.3.

Translational Joint: A Translational joint provides a linear sliding movement between two bodies.

Fig.4. 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.

PROCEDURE

The different types of joints are created between two rigid bodies in LS-DYNA using keyword *CONSTRAINED_EXTRA_NODES and between two deformable bodies using *CONSTRAINED_NODAL_RIGID_BODY.

I. Joints Between Two Rigid Bodies

1. Spherical Joint:

Fig.5 FE Model for spherical Joint Creation.

Open LS-PrePost, using options under Element and Mesh>>Shape Mesher>> Entity>>Sphere Shell, create two parts as shown in Fig.5. The elements of the outer sphere shell are deleted using option Element editing to get the necessary shape.

Fig.6 Section Property.

Fig.7 Material Property.

The Section and material property as shown in fig.6 and fig.7 are assigned to the parts.

Note: The section and material property parameters considered are common for all types of joints.

A pair of nodes is created using the option under Element Tools>>Node Editing>>Create, i.e node 305 and 306. The node 305 is constrained to part 1 and node 306 to part 2 using *CONSTRAINED_EXTRA_NODES card as shown in fig. 8 and fig.9.

Fig.8 Node 305 constrained to part 1.

Fig.9 Node 306 constrained to part 2.

Fig.10 Spherical joint creation.

The spherical joint is created using *CONSTRAINED_JOINT_SPHERICAL card with one node pair i.e node N1 is 305 for part 1 and Node N2 is 306 for part 2.

Fig.11 Initial velocity

The initial velocity of 20 mm/ms is assigned to the moving part in the rotational X, Y, Z axis.

Fig.12 Control timestep

The value of Initial time step size (DTINIT) is set as 0.01 ms.

Fig.13 Control termination

The termination time is set as 5 ms.

The keyword file is saved using suitable name with ‘.k’ extension and made to run in LS-DYNA program manager.

2. Revolute Joint:

Fig.14 FE Model for Revolute Joint.

Open LS-PrePost, using options under Element and Mesh>>Shape Mesher>> Entity>>4N Shell, create two parts as shown in Fig.14, i.e red plate being part 1 and green plate is part 2.

The material and section properties assigned to the parts are same as that of spherical Joint.

Fig.15 Nodesets constrained to part 1 and part 2.

Two pairs of nodes are created using the option under Element Tools>>Node Editing>>Create, i.e node 101-102 and 103-104. The nodes 101 and 103 is constrained to part 1 and nodes 102 and 104 to part 2 using *CONSTRAINED_EXTRA_NODES card as shown in fig.15.

Fig.16 Revolute joint creation.

The revolute joint is created using *CONSTRAINED_JOINT_REVOLUTE card with nodes N1 and N3 of part 1 and nodes N2 and N4 of part 2

Fig.17 Boundary SPC set with all dof’s fixed on part 1.

The nodes of the part 1 as shown in fig.17 is constrained in all degrees of freedom.

Fig.18 Boundary prescribed motion on node 173.

Fig.19 Displacement Load curve (LCID).

Fig.20 Timestep curve (LCTM).

The control timestep is defined using LCTM curve as shown in fig.20.

The termination time is set as 10 ms.

The keyword file is saved using suitable name with ‘.k’ extension and made to run in LS-DYNA program manager.

3. Cylindrical Joint:

Fig.21 FE Model for Cylindrical Joint

Open LS-PrePost, using options under Element and Mesh>>Shape Mesher>> Entity>>Cylinder Shell, create two parts as shown in Fig.21, i.e red cylinder being part 1 and green cylinder is part 2.

The material and section properties assigned to the parts are same as that of spherical Joint.

Two pairs of nodes are created using the option under Element Tools>>Node Editing>>Create, i.e node 321-322 and 323-324. The nodes 321 and 323 is constrained to part 1 and nodes 322 and 324 to part 2 using *CONSTRAINED_EXTRA_NODES card.

Fig.22 Cylindrical joint creation.

The cylindrical joint is created using *CONSTRAINED_JOINT_CYLINDRICAL card with nodes N1 and N3 of part 1 and nodes N2 and N4 of part 2.

Fig.23 Initial velocity

The initial velocity of 10 mm/ms is assigned to the part 1 in the X-axis.

The value of Initial time step size (DTINIT) is set as 0.01 ms.

The termination time is set as 5 ms.

The keyword file is saved using suitable name with ‘.k’ extension and made to run in LS-DYNA program manager.

4. Translational Joint:

Fig.24 FE Model for translational Joint

Open LS-PrePost, using options under Element and Mesh>>Shape Mesher>> Entity>>Box Shell, create two parts as shown in Fig.24, i.e red box being part 1 and green box is part 2.

The material and section properties assigned to the parts are same as that of spherical Joint.

To define Translational joint three pairs of nodes are created. Using the option under Element Tools>>Node Editing>>Create, two pairs of nodes are created 1001-1002 and 1003-1004 which is coincident and collinear. The third pair 1005-1006 is coincident and slightly away from the axis of other two pairs but in-between the two pairs. The nodes 1001, 1003 and 1005 is constrained to part 1 and nodes 1002, 1004 and 1006 to part 2 using *CONSTRAINED_EXTRA_NODES card.

Fig.25 Translational joint creation.

The translational joint is created using *CONSTRAINED_JOINT_TRANSLATIONAL card with nodes N1, N3 and N5 of part 1 and nodes N2, N4 and N6 of part 2

Fig.26 Initial velocity

The initial velocity of 10 mm/ms is assigned to the part 1 in the X-axis.

The value of Initial time step size (DTINIT) is set as 0.01 ms.

The termination time is set as 5 ms.

The keyword file is saved using suitable name with ‘.k’ extension and made to run in LS-DYNA program manager.

II. Joints Between Two Deformable Bodies

The steps required to create a joint between two deformable bodies are same as that of rigid bodies except few changes i.e,

1. *MAT_ELASTIC material card is used instead of *MAT_RIGID card.
2. Instead of using *CONSTRAINED_EXTRA_NODES card *CONSTRAINED_NODAL_RIGID_BODY (CNRB) is used to constrain the nodes to the necessary part.
3. The initial velocity is assigned using *INITIAL_VELOCITY card instead of *INITIAL_VELOCITY_RIGID_BODY card.

1. Spherical Joint:

The parts for spherical joint are created and assigned with section and material properties similar to the spherical rigid joints.

Fig.27 Material property.

Fig. 28 Spherical joint created with CNRB.

Using Create Entity>>Constrained>>Nodal Rigid Body (CNRB) option the nodes generated are linked between two deformable parts for creating spherical joint.

The spherical joint is created using *CONSTRAINED_JOINT_SPHERICAL card with one node pair i.e node N1 is 305 for part 1 and Node N2 is 306 for part 2.

Fig.29 Initial velocity

The initial velocity of 20 mm/ms is assigned to the moving part in the rotational X, Y, Z axis.

The value of Initial time step size (DTINIT) is set as 0.01 ms.

The termination time is set as 5 ms.

The keyword file is saved using suitable name with ‘.k’ extension and made to run in LS-DYNA program manager.

2. Revolute Joint:

The parts for revolute joint are created and assigned with section and material properties (*MAT_ELASTIC) similar to the revolute rigid joints.

Two pairs of nodes are created using the option under Element Tools>>Node Editing>>Create, i.e node 101-102 and 103-104. The nodes 101 and 103 is constrained to part 1 and nodes 102 and 104 to part 2 using *CONSTRAINED_NODAL_RIGID_BODY under create Entity option.

Fig.30 Revolute joint created with CNRB.

The revolute joint is created using *CONSTRAINED_JOINT_REVOLUTE card with nodes N1 and N3 of part 1 and nodes N2 and N4 of part 2.

The nodes of the part 1 is constrained in all degrees of freedom using boundary SPC set and boundary prescribed motion is assigned to node 173 similar to revolute rigid joints.

The control timestep is defined using LCTM curve.

The termination time is set as 10 ms.

The keyword file is saved using suitable name with ‘.k’ extension and made to run in LS-DYNA program manager.

3. Cylindrical Joint:

The parts for cylindrical joint are created and assigned with section and material properties (*MAT_ELASTIC) similar to the cylindrical rigid joints.

Two pairs of nodes are created using the option under Element Tools>>Node Editing>>Create, i.e node 321-322 and 323-324. The nodes 321 and 323 is constrained to part 1 and nodes 322 and 324 to part 2 using *CONSTRAINED_NODAL_RIGID_BODY under create Entity option.

Fig.31 Cylindrical joint created with CNRB.

The cylindrical joint is created using *CONSTRAINED_JOINT_CYLINDRICAL card with nodes N1 and N3 of part 1 and nodes N2 and N4 of part 2

The initial velocity of 10 mm/ms is assigned to the part 1 in the X-axis.

The value of Initial time step size (DTINIT) is set as 0.01 ms.

The termination time is set as 5 ms.

The keyword file is saved using suitable name with ‘.k’ extension and made to run in LS-DYNA program manager.

4. Translational Joint:

The parts for translational joint are created and assigned with section and material properties (*MAT_ELASTIC) similar to the translational rigid joints.

To define Translational joint three pairs of nodes are created. Using the option under Element Tools>>Node Editing>>Create, two pairs of nodes are created 1001-1002 and 1003-1004 which is coincident and collinear. The third pair 1005-1006 is coincident and slightly away from the axis of other two pairs but in-between the two pairs. The nodes 1001, 1003 and 1005 is constrained to part 1 and nodes 1002, 1004 and 1006 to part 2 using *CONSTRAINED_NODAL_RIGID_BODY under create Entity option.

Fig.32 Translational joint created with CNRB.

The translational joint is created using *CONSTRAINED_JOINT_TRANSLATIONAL card with nodes N1, N3 and N5 of part 1 and nodes N2, N4 and N6 of part 2

The initial velocity of 10 mm/ms is assigned to the part 1 in the X-axis.

The value of Initial time step size (DTINIT) is set as 0.01 ms.

The termination time is set as 5 ms.

The keyword file is saved using suitable name with ‘.k’ extension and made to run in LS-DYNA program manager.

OUTPUT

I. Joints Between Two Rigid Bodies

1. Spherical Joint:

2. Revolute Joint:

3. Cylindrical Joint:

4. Translational Joint:

II. Joints Between Two Deformable Bodies

1. Spherical Joint:

2. Revolute Joint:

3. Cylindrical Joint:

4. Translational Joint:

CONCLUSION

1. The keyword files necessary to demonstrate spherical, revolute, cylindrical, and translational joints between two rigid bodies and two deformable bodies are created and simulated.
2. Learned to create different types of joints using *CONSTRAINED_EXTRA_NODES and *CONSTRAINED_NODAL_RIGID_BODY between rigid and deformable bodies respectively. 

Google Drive Link: Joint Creation