Week - 4 - Crash Box Simulation

OBJECTIVE: 

  1.To run the Simulation for the given crash box mesh model

• Keeping the Unit system in g-mm-ms
• Creating the Rigidwall Using the `^**`Rigidwall_keyword.

with the following case set ups:

 Case 1. 

1. Elastic card for the Material is used and the properties are that of the Steel  .
2.  Using the Intial velocity card with velocity of 50 Kmph.
3.  Keeping the Crash Box thickness at 1.2mm.
4. Runing the Simulation for 10ms . 

 Case 2.  

1. Elastic card for the Material is used and the properties are that of the Steel  .
2. Using the Prescribed motion Set card to gradually increase the velocity to 50kmph .
3.  Keeping the Crash Box thickness at 1.2mm.
4. Runing the Simulation for 10ms . 

Case 3.

         Peiecewise_Linear_Plasticity  card for the Material is used and the properties are that of the Steel  .

1. Using the Prescribed motion Set card to gradually increase the velocity to 50kmph .
2. Keeping the Crash Box thickness at 1.2mm.
3. Runing the Simulation for 10ms . 

Case 4.

      Running the above three cases again by changing the Thickness of the model to 1.5mm

2. For the Above case set ups Obtain the Following results 

1. Animation of the final simulation
2. Cross-sectional force generated in the middle of the crashbox (along its length)
3. Acceleration plot of a node in the middle of the crashbox (along its length)
4. Maximum directional stress and strain along the length of the crashbox (X strain, Y strain etc)
5. Plot of all energies (total, internal, kinetic, hourglass, sliding)

3.  and comparing the accelerations and the Stress strain plots of 1.2mm and 1.5mm thickness crashboxes.

 

CASE SET UP :

 1.Creating the Rigid Wall

       The Rigid wall is created by using the Create entity tool in the model and parts toolbar. The Rigid wall used is the Planar form  & is created by defining the Nodes and the Vectors by picking the nodes on the crash tube in the order of the direction in which the normal of the rigid wall is to be created i.e, in the direction opposite to that of the  crash tube travel.

Fig 2 Creating the Rigid wall

       The wall created is exactly at the peripehery of the crash tube and hence it has to be moved away slightly by using the translate comand in the Create entity tool.

Case 1 :

i. Creating the Material properties

         The Material card 001_elastic is chosen and the material card is created by entering the material properties of the steel in the 001_Elastic material card.

Fig 3 Creating the Material card type

ii.Creating the Section Id

    The Section card Shell is chosen in the Keyword manager and the Elform 2 is chosen in the Section card as well as a thickness of 1.2 mm is assigned to the Section ID created.

Fig 4 Creating the Section ID card

iii.Assigning the Section ID and the Material to the PartId

       The MaterialID and the Section Id which have been created are assigned to the PartId i.e, The Crash tube.

 

Fig 5 Assigning the Material and the section ID to the Part

iv. Creating Intial velocity card and assigning intial velocity of 50 kmph to the Crash tube

     a) Generating the node set for applying the Intial velocity

        The Seperate node set for applying the Intial velocity is created by selecting all the nodes of the crash tube.

     b)Selecting  the created nodeset and assigning the Intial velocity in the Intial velocity card.

         The newly created nodeset is assigned in the intial velocity card and velocity of 13.89 mm/ms (50 kmph) is entered.

       

Fig 6 Assigning the Initial velocity to the crash tube  

v.Creating the Database card for the Output requests

   a) Creating the Section for the Sectional forces

          The Section is created under the database in the Create entity toolbar. The nodes are selected in the direction of the nomal which is oppposite in direction to the crash tube velocity.  

Fig 7 Creating the Section for the Cross sectional forces

      b)Selection of the time history nodes

         The node for which the time history plot is to be plotted is selected under the history keyword in the entity creation toolbar. In this case the middle node along the face of the length is being selected for ploting the time history plots.

Fig 8 Selecting the node for Time history plot

    c) Giving the output request in the Database card 

         The requests for the ASCII plots such as the GLSTAT for plotting the energies , MATSUM ,RWFORCE(Rigid wall forces) ,SECFORCE(Cross Sectional force) and NODOUT(Nodal Time history plot) are given in the database card as well as the request for the d3plot is also given in the same card.

Fig 9 Givng the Ouput requests in the database card

 

vi. Creating the Contact cards

      Here, the contact card for the Automatic_single_Surface card is created for the self contact. All the nodes are the cradsh tubes are selected for both slave and master nodes.

Fig 10 Creating the self contact cards

 vii.Creating the Control Termination card

      The Control termination card is created so that the time for which the simulation must be run i.e, ENDTIM =10 ms  is enetred.

Fig 11 Creating the Control termination card

 

Case 2.

  i. Deleting the Intial Velocity card and Using the Prescribed motion Node card.

   a) Creating the Velocity Curve.

                    The Velocity curve with gradually in crease in value of velocity with time is created under the define card in the Create entity tool.

  Fig 12 Plotting the Imposed velocity curve  

  b) Creating the CNRB Element.

                     The Rigid body is created by selecting all the outer periphery nodes in the Constrianed tool in the create entity. The master node gets created in the center of the selected nodes.

 

Fig 13 Creating the Nodal rigid body (CNRB)

 c) Creating the prescribed motion nodes card

 While creating the Prescribed Motion Node  Card the following values are Input :

• The master node of the Nodal rigid body (CNRB) is selected under the nodal rigid body.
• The Dof is made equal to '0' in order to have translational motion in X- direction.
• The VAD is made equal to '0' for Imposing the Velocity.
• The Velocity curve ID is selected for the LCID.
• The Scale Factor is Kept at 1.00. 

 

Case 3.

 

  i. Using the Piecewise Linear plasticity card for the Material

       The card for the Material is changed  from Linear material card to the Piecewise Linear Plasticity.The required values such as the corresponding stress values for the plastic strain values are entered.

Fig 15 Creating the Piecewise Linear Plastic Material Card

    ii. Assigning the material card to the crash tube 

          The material card is assigned to the Crash Tube PartID.

Fig 16 Assigning the material card to the part ID

Case 4 :

  All the Above three cases are Run by Chaging the thickeness value of the Crash tube in the section card.

Fig 17 Changing Section thickness from 1.2mm to 1.5mm

EXECUTION :

 All the above cases are saved as seperate Keyword(.k)Files and run in the LS- RUN.

RESULTS :

1. Cross sectional forces generated in the middle of the box

 Fig 18 Cross Sectional Forces_case1_case2_case3

INFERENCE :  

  The impact in case of the Intial Velocity happens at 2ms(approx) where as in case of the Imposed Velocity happens at 6.2 ms.Hence, it can be seen that the highest Resultant Force can be seen in case of the Elastic Material with Imposed Velocity at the time of the impact.i.e, 78 KN.

 2. Acceleration plot of the Node in the middle of the box along the length 

Fig 19 Nodal acceleration for Case 1,Case 2 & Case 3

INFERENCE:

  At the time of the impact, Nodal acceleration is found to be the highest in case of Elastic material with Intial Velocity. The Overall Nodal acceleration is found to be highest in case of the Elastic material with Imposed Velocity.

3. X-Direction Stress for all the cases

CASE 1:

Fig 20 X- direction stress for Elastic Material with Intial Velocity

CASE 2 :

Fig 21 X- Direction Stress for Elastic Material with Imposed Velocity

 CASE 3 : 

 Fig 22 X- Direction Stress for Plastic Material with Imposed Velocity

INFERENCE :

     The Maximum stress is induced in case3 i.e, in case of Plastic material with imposed Velocity at the time of Impact. 

4. Plot of all Energies

 i. Kinetic Energies

       

 Fig 23 Kinetic Energies comparison

  INFERENCE :

     The Kinetic energy is found to be highest at the time of the Impact in Case 2 i.e, In elastic material with Imposed velocity.

ii. Internal Energies

    

INFERENCE :

     The Internal energy is found to be very negligible and constant in CASE1 i.e, in case of the Elastic material with Intial Velocity where as there is a sudden increase in the Internal Energies of the crash Tube in case of the Elastic and Plastic materials with Imposed Velocity.

iii.Total Energies

Fig 25 Total Energies comparison

INFERENCE :

     The Total energy is found to be very negligible and constant in CASE1 i.e, in case of the Elastic material with Intial Velocity where as there is a sudden increase in the Total Energies of the crash Tube in case of the Elastic and Plastic materials with Imposed Velocity.

iv. Hourglass Energies

Fig 26 Hourglass Energies Plot

INFERENCE :

      The hourglass Energies for all the three cases have been found to be negligible.

v. Sliding Energies

Fig 27 Sliding Energies Comparison

INFERENCE :

         The Sliding Energy for the Case 1 i.e, Elastic material with intial Velocity is very negligilble where as in case 2 i.e, Elastic material with Imposed velocity decreses and goes negative and in case 3 i.e Plastic material with Imposed velocity increases dramatically after the contact with the rigid wall.

 5. Comparison of Accelerations between 1.2mm thickness crash tube and 1.5mm Thickness Crashtube

Case1.

Fig 28 Nodal Acceleration_1.5mm_1.2mm_comparison

INFERENCE :

      There is a slight decrease in the Nodal Acceleration on Increase in the Thickness of the crash tube.

Case 2.

Fig 29 Nodal Acceleration_1.5mm_1.2mm_comparison

INFERENCE :

      There is a slight decrease in the Nodal Acceleration on Increase in the Thickness of the crash tube.

Case 3.

Fig 30 Nodal Acceleration_1.5mm_1.2mm_comparison

INFERENCE :

      There is a slight decrease in the Nodal Acceleration on Increase in the Thickness of the crash tube.

6. Comparison of the Stress Strain Plots between 1.5mm thick and 1.2mm thick Crashtubes

Case 1.

i. Stress comparison

 

 Fig 31 Stress_1.5mm

 

   

 Fig 32 Stress_1.2mm

 

INFERENCE : 

 Maximum Stress at the time of the contact with the Rigid wall  is nearly twice in case of the 12mm thick crash tube as commpared to the 1.5mm crash tube.

ii. Strain

  The Strian values are zero since the Material used is Elastic material.

 

Case 2.

 

 Fig 33 Stress_1.5mm  

 

  Fig 34 Stress_1.2mm

INFERENCE :

   There isn't too much of difference in the stress values of the crash tubes of 1.5mm thickness and 1.2mm thickness.

ii. Strain 

        The Strain values are zero since the material used are elastic in nature.

 

Case 3.

Fig 35 Stress _1.5mm

Fig 36 Stress _1.2mm

INFERENCE :

   There isn't too much of difference in the stress values of the crash tubes of 1.5mm thickness and 1.2mm thickness.

ii.Strain

  Fig 37 Strain_1.5mm   

Fig 38 Strain_1.2mm

INFERENCE :

     There is decrease in the strain values with the Increase in the thickness.

 

CONCLUSION : 

  All the cases were simulated successfully and all the results were tabulated for the same.