Challenge

week-11 Joint creation and Demonstration

RRisheb Rasheed28 Oct 2021

JOINTS

Aim

To create translational, revolute, spherical and cylindrical joints for rigid and deformable bodies using Ls-Dyna.

Theory

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”.

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

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

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

Create 2 different shells using shape mesher -> Box shell

Create a section shell card

Create material for rigid and deformable

Note:Use rigid for rigid and elastic for deformable bodies for all cases.

Create 2 sets of nodes using nodedit option

Pair any 2 nodes together and assign them to different parts .That is pair one of 73,74 and one of 75,76 for each part.

Create the revolute joint accordingly.

Define a load curve.

And a timestep curve

Constrain these nodes along all axis.

Define the prescribed motion node

Create the control timestep and termination cards.

Same for all cases
Create database cards , matsum and glstat in Ascii

For deformable, you connect the create nodes to the part nodes using CNRB constraints and change material to elastic for both parts. Note:Disable CrePNode option

Rigid

Deformable

Spherical

Use create sphere shell and solid to get shown.Delete elements of outershell.

Define the sections.

Create nodes at the centre of the sphere for each part.

Similar to the previous case create CNRB for deformable and extra_nodes_set for rigid.

Define the spherical joint.

Change prescribed motion from translational to rotational.

Rigid

Deformable

Cylindrical Joint

Use create cylindrical shell to create as shown

Define a section shell card.

Create 2 nodes at the top and bottom circle centre, use extra nodes set and assign a pair from top and bottom to each part.

Define the cylindrical joint.

For deformable remove the extranodeset and create CNRB instead.

Rigid

Deformable

Translational Joint

Use box solid and box shell option to get the desired arrangement.

Delete elements of the outer shell and translate the inner box accordingly.

Create 3 sets of nodes as shown.Note the centre node set should not be collinear to the other 2 node sets.

Use extranodeset option and set nodes from each pair to the 2 parts.

Define the translational joint.

Define translational displacement along the z plane.

Set the corner nodes of the outershell as fully constrained on all axis.
Note: while its fine to set the entire part for rigid, doing so for deformable will cause errors with CNRB creation.