week-11 Joint creation and Demonstration

JOINT CREATION AND DEMONSTRATION USING LS-DYNA

 

 

INTRODUCTION:

 

A mechanical joint is a machine component that connects one or more mechanical parts to another. Mechanical couplings can be either temporary or permanent, and the majority of them are meant to be dismantled. Most mechanical joints are intended to enable relative movement of these machine elements in one degree of freedom while restricting movement in one or more others.

 

• REVOLUTE JOINT: A revolute joint (also known as a pin joint or hinge joint) is a kinematic pair with one degree of freedom that is commonly employed in mechanisms and machines. The joint restricts two bodies' motion to pure rotation along a shared axis. Nodes 1 and 2 are coincident, as are nodes 3 and 4. Nodes 1 and 3 are rigid body A, whereas nodes 2 and 4 are stiff body B. The two stiff bodies' relative motion is limited to rotations about the axis created by the two sets of coinciding nodes. This axis is known as the "centerline."

 

 

• SPHERICAL JOINT: A spherical joint, often known as a ball-and-socket joint, allows for three relative rotations of the two linked segments and is commonly used to mimic the hip and glenohumeral joints. The stiff bodies' relative motion is restricted, such that nodes that are originally coincident stay coincident. The socket's node is not interior to the socket in the previous example—LS-DYNA does not require rigid body nodes to be interior to the body. 

 

 

• CYLINDRICAL JOINT: A cylindrical joint is a kinematic pair with two degrees of freedom that is utilized in mechanisms. Cylindrical joints connect two bodies along a single axis while allowing them to rotate and slide around that axis. As an example, consider an unsecured axle installed on a chassis that may freely spin and translate. One example is the rotating poles on a table football. This joint is created by easing the restrictions along the midline of the rotating joint. This joint allows for relative rotation and translation along its axis.

 

 

• TRANSLATIONAL JOINT: A translational joint is a form of joint that allows one part to move along a vector in relation to another. The pieces can only translate, not rotate, in relation to one another. This joint has one degree of freedom in translation and zero degrees of freedom in rotation. This is a cylindrical joint that has a third pair of off-centerline nodes that limit rotation. The two hard bodies are glued together apart from translation along the centerline. 

 

 

 

AIM:

 

1. Using the manual (*CONSTRAINED_JOINT keyword) demonstrate spherical, revolute, cylindrical, and translational joints between two rigid bodies and two deformable bodies. 
2. To demonstrate the joints' working, rotation and translatory motions should be shown
3.  The final submission should include input files for each of the joints and animations showing their results. 

 

 

EXPLANATION:

 

REVOLUTE JOINT

 

 RIGID BODIES 

 

• In this assignment there is no model given as an input file rather we have to create several keyword files with the provided instructions. Four types of joints are created for this task with two cases of rigid and deformable bodies. Hence without further ado, the revolute joint is initiated by creating two four-noded 2D-shell element boxes. Mesh>ShapeM tool is used to create the parts for all 4 joints in this assignment. The dimensions for the shells are displayed below with respect to the Geometric coordinate system. The units used for all the following 4 joints are Kg, mm, and ms respectively.   

 

 

• As described in the introduction we create nodes 501 and 503 for the first part and 502 and 504 for 2nd part. 501-502 and 503-504 are coincident likewise. The series of middle nodes are created by using the option shown below in the Node Editing dialog box.

 

• The section shell card as shown below is inserted with the provided values for all 4 joints.

 

 

 

• The Mat_rigid card with these calculated values by assuming hardened steel as a rigid body is considered for all 4 types of joints in this assignment.

 

 

 

 

• Henceforth we create two node sets of 501-503 and 502-504 for each part.  

 

 

• We use the Constrained_Extra_Node_Set keyword for rigid bodies in all 4 types of joints. The Node sets developed earlier are designated to this card accordingly. 

 

 

• The nodes that are considered with each part are entered in Constrained_Joint_revolute in a sequential manner of revolution between both parts. 

 

 

•  The displacement curve is established for this case of a rigid body with computed values.

 

 

•  We use an SPC card for one part that remains constrained in all axis and give a prescribed motion along the z-translational axis w.r.t the load curve Id generated earlier. 

 

 

• We use Explicit analysis for all these 4 joints so the control_timestep card is employed here. The initial time step value is either computed by a curve Id or given directly as 0.01 for all 4 modes.  

 

 

• Furthermore, Control_termination card and binary d3plot card with given values are also inserted.

 

 

 

 

• Lastly, model checking is done and errors if found are rectified and the simulation is run effectively. 

 

 

• The final simulation shows one part constrained and the other part revolving along the z-axis.

 

 

 

  DEFORMABLE BODIES 

 

• In the case of deformable bodies, we choose Mat_elastic card assuming rubber band material with the given values.

 

 

•  In the case of deformable bodies, we create Constrained_Nodal_rigid_bodies which are connected to each principal node set. So in this case we don't use the Constrained_Extra_Node_set card. The step-by-step process is done with utter caution otherwise the CNRB will misbehave during simulations. The process for the Revolute joint case is shown below, also in PNID, we put the value of our principal nodes and then select other nodes from top to bottom of each body.

 

 

 

 

 

 

• The CNRBs generated here are transferred in the middle on the axis of rotation for each body by Ele Tol>Transf tool as displayed below.

 

 

 

  

• The rest of the process is followed the same as done in the rigid body case earlier except change some values as assigned below.

 

 

 

 

 

 

 

 

 

SPHERICAL JOINT

 

 RIGID BODIES 

 

• In spherical joint two spheres are created with equal mesh density but different radii. The outer sphere is sectioned in the middle whilst deleting the upper region. 

 

 

 

 

 

• Two nodes namely 701 and 702 are created in this type of joint which are constituted to each sphere shell respectively.

 

 

 

 

• These nodes are inputted in the Constrained_Extra_Node_Set card accordingly. 

 

 

 

• The Constrained_Joint_Spherical card is used for the spherical joint model. 701 and 702 nodes are inserted in sequence for this keyword.  

 

 

• We use initial velocity from now onwards rather than displacement just to ease the briefing and evaluation of this assignment. So we provide an initial velocity of 35mm/ms in X, Y, and Z-rotational direction only. 

 

 

• The termination time and other mandatory cards required for the joint creation and demonstration process are the same as shown earlier. 

 

 

 

 

 

  DEFORMABLE BODIES 

 

• In the case of deformable bodies, we use the Mat_Elastic card as aforementioned earlier with the same values. 

 

  

• In this case, CNRBs are created for each sphere with 801 and 802 as principal nodes.

 

 

• The SPC is applied on the outer sphere to keep its motion constrained w.r.t the inner sphere in all directions.

 

 

 

• The node set for initial velocity is established by selecting all nodes of the inner sphere.

 

 

• The rest of the cards are repeated just like in the rigid body case for the spherical joint. 

 

 

 

 

 

 

CYLINDRICAL JOINT

 

 RIGID BODIES 

 

• In a cylindrical joint, we create two cylindrical shells, inner and outer respectively with different radii and lengths as shown below. 

 

 

 

 

 

 

 

 

 

•   Two node pairs are created which are associated with each cylindrical shell part. One pair is of 501-503 for the outer cylinder and 502-504 for the inner cylinder. All 4 nodes are distanced pertaining to the instructions given in LS-Dyna Manual VOL-1 correspondingly. 

 

 

 

 

• Two node sets for each cylindrical shell are generated and inserted in the Constrained_Exta_Node_set card. 

 

 

 

 

• All 4 nodes are sequentially placed in the Constrained_Joint_cylindrical card.

 

 

• The initial velocity is given to the inner cylindrical shell part by selecting all its nodes.

 

 

• The control and database cards used in the cases are repeated in the same manner for this type of joint as well.

 

 

 

 

 

• In the simulation, we observed that the inner cylinder is rotating and translating along the x-axis specifically while as the outer cylinder is constrained in all axis.

 

 

 

  DEFORMABLE BODIES 

 

• In this case, we keep the mesh density for both cylinders symmetrical and create the rest of the dimensions as done in the rigid body case. 

 

 

• The CNRBs are created with principal node pairs 401-403 for the inner cylinder shell and 402-404 for the outer cylinder shell specifically.

 

 

• The rest of the method is repeated like done in earlier joints for deformable bodies. 

 

 

 

 

 

 

 

 

 

TRANSLATIONAL JOINT

 

 RIGID BODIES 

 

• In translational joints, two-box shells are created with the dimensions as described below in the pictures. We delete the 2 faces of both shells respectively in order to attain two hollow shells as shown below.

 

 

 

 

 

 

 

 

 

 

 

• The node pairs established here are obtained by following the instructions of the translational joint in LS-Dyna manual Vol-1. 501,503,505 nodes are associated with the inner box shell and 52,504,506 belong to the outer box shell part.

 

 

 

 

 

 

 

• The rest of the cards and methods are repeated while some values are altered. 

 

 

 

 

 

 

• In this type of simulation, the inner box shell only translates in the x-direction while all directions are constrained for both shells.

 

 

 

  DEFORMABLE BODIES 

 

• In deformable bodies, the same hollow box shells are used except the node pairs created earlier act now as principal nodes for CNRBs of both shells correspondingly.

 

 

 

 

 

 

• The initial velocity card and other mandatory cards required to run the simulation are repeated most likely again.

 

 

 

 

 

 

•  This simulation follows the rigid bodies simulation in an exact manner without any change in motion except it is a bit slow with the same initial velocity and other parameters.

 

 

 

 

CONCLUSION:

 

1. The simulations for both rigid and deformable bodies are acquired in this assignment for all 4 types of joints prescribed in the objectives. 
2. The relative motion in deformable bodies is observed to be lower than the rigid bodies in all 4 types of joints with the same parameters. 
3. The applications of CNRBs are thoroughly evaluated in this task by testing them with all the given joints.
4. The stresses and strains formulated in rigid bodies is negligible compared to deformable bodies for all the joints facilitated above.