Crash Box Simulation

AIM:

To simulate a crash test for a crash box for different values of thickness –

Case 1: 1.2mm

Case 2: 1.5mm

OBJECTIVES:

• To create a solver deck to perform the crash test simulation.
• To enter the values in g mm ms unit system.
• To assign steel material properties for the crash box and rigidwall for the rigid wall.
• To assign initial velocity for the crash box at 50kmph.
• To create contact card.
• To create control keywords.
• To measure the cross section force generated at the middle of the crash box.
• To plot the total, internal, kinetic, hourglass, sliding energy graphs.
• To compare the accelerations and stress/strain plots of 1.2/1.5mm crashbox.
• To run the .K file and evaluate the results.

UNIT SYSTEM USED: G MM MS

BOUNDARY CONDITIONS:

• The crash box should crash onto the rigidwall.
• Material of crash box is Steel.
• Initial velocity of crash box is 50kmph.
• The crash box should rebounce completely or it buckles and folds in the axial direction so as to come in self-contact.

MATERIAL PROPERTIES:

• Crash Box: Here, the rigid wall is to be considered as the concrete road.

Density: 0.0078g/mm³

Youngs Modulus (E): 210000g/mm*ms²

Poissons Ratio: 0.3

Yield Strength: 350 g/mm*ms²

PROCEDURE:

• CASE 1: THICKNESS_1.2MM
• Importing:
• FILE > OPEN > LS DYNA KEYWORD FILE > NEW_CRASH_BOX.
• 
• Then, go to MODEL AND PART COMMAND > KEYWORD MANAGER.
• We can check the keywords in the model.
• Part Check:
• Go to MODEL AND PART COMMAND > PART DATA.
• We can see that the model consists only 1 part i.e. crash box.
• Now, rename the parts as crash box.
• Now, in the part card we have to define section and material, so let’s create a Section and Material card.
• *Section:
• Go to MODEL AND PART COMMAND > KEYWORD MANAGER > ALL > SECTION > SHELL > TITLE = CRASH_BOX_PROP > SECID = 1 > T1 = 1.2 > ACCEPT > DONE.
• 
• This will create a shell section which can be defined for the crash box.
• *Material:
• Go to MODEL AND PART COMMAND > KEYWORD MANAGER > ALL > MATERIAL > 24-PIECEWISE_LINEAR_PLASTICITY > TITLE = STEEL > MID = 1 > RO = 7.85E-3 > E = 2.1E5 > PR = 0.3 > SIGY = 350 > EAN = 1E4 > FAIL = 1E21 > ACCEPT > DONE.
• 
• Now, go to MODEL AND PART COMMAND > KEYWORD MANAGER > MODEL > PART > ASSIGN > SECTION AND MATERIAL.
• *Rigid_wall_planar:
• Go to, MODEL AND PART COMMAND > KEYWORD MANAGER > ALL > RIGIDWALL > PLANAR > XT = -20MM > ACCEPT > DONE.
• 
• This will create a rigidwall plane at 20mm distance from the crash box.
• *Initial_Velocity:
• Now, we have to define initial velocity for the Cell_phone.
• Go to, MODEL AND PART COMMAND > KEYWORD MANAGER > ALL > INITIAL > VELOCITY > NSID = 1 > VX = -13.89 MM/MS > APLLY > DONE.
• 
• *Contact_Automatic_Single_Surface:
• Now, we have to define Contact for the crash box.
• Go to, MODEL AND PART COMMAND > KEYWORD MANAGER > CONTACT > AUTOMATIC_SINGLE_SURFACE > CID =1 > TITLE = CONTACT > SSTYP = 3 > SSID = 1> ACCEPT > DONE.
• 
• This will define the contact as Slave for the Cell_Phone and Master for the Rigid_wall.
• *Control_Termination:
• Now, we have to define Control_Termination card for the simulation time.
• Go to, MODEL AND PART COMMAND > KEYWORD MANAGER > CONTROL > TERMINATION > ENDTIM = 5 MS > ACCEPT > DONE.
• 
• *Database_Binary_D3plot:
• Go to, MODEL AND PART COMMAND > KEYWORD MANAGER > DATABASE > BINARY D3PLOT > DT = 0.1 > ACCEPT > DONE.
• 
• This will create the binary D3plot output files.
• *Database_ASCII:
• And finally we have to define the output results.
• Go to, MODEL AND PART COMMAND > KEYWORD MANAGER > DATABASE > ASCII > GLSTAT > DT = 0.1 MS > MATSUM > DT = 0.1 > RCFORC = 0.1 > SLEOUT = 0.1 > ACCEPT > DONE.
• 
• This will provide the output results.
• *Database_Cross_Section_Plane:
• Go to, MODEL AND PART COMMAND > KEYWORD MANAGER > DATABASE > CROSS_SECTION_PLANE > CSID = 1 > PICK > PLANE.
• 
• This will create a cross section plane in the middle of the crash box.
• *Database_History_Node:
• Go to, MODEL AND PART COMMAND > KEYWORD MANAGER > DATABASE > HISTORY_NODE > ID1 > PICK NODE > INSERT > ACCEPT > DONE.
• 
• This will provide acceleration plot for the node.
• Model check:
• The final step is to perform Model check.
• Go to, MODEL AND PART COMMAND > MODEL CHECK > DONE.
• 
• LS_Run:
• Now, open LS RUN > OPEN THE FILE > RUN.
• The solver will solver the model and check for the Normal Termination message at the end of the solver screen.

• CASE 2: THICKNESS_1.5MM
• Open the same file and change the thickness in Section card as 1.5mm.
• 

• Post-Processing:
• CASE 1: THICKNESS_1.2MM
• Open LS Pre-Post.
• FILE > OPEN > LS DYNA BINARY PLOT.
• Go to, POST > FRINGE COMPONENT > STRESS > VON MISSES > DONE.
• 
• To plot the Energy graphs go to, POST > ASCII > LOAD FILE > GLSTAT > SELECT ENERGIES > PLOT > DONE.

• 
• We can see the internal energy increases at the point when the crash box comes in contact with the rigid wall.

• 
• The Kinetic energy reduces on impact with the rigid wall.

• 
• The kinetic energy is converted into internal energy when the box crashes on the rigid wall.

• 
• There is no hourglass energy seen in the simulation.

• 
• No sliding is seen, that means the crash box rebounds after impact with the rigid wall.

• 
• The acceleration of a node along the length is plotted and the peak value is about 2.4g.

• 
• The section force value is plotted with respect to time.

• 

• 

• CASE 2: THICKNESS_1.5MM
• Open LS Pre-Post.
• FILE > OPEN > LS DYNA BINARY PLOT.
• Go to, POST > FRINGE COMPONENT > STRESS > VON MISSES > DONE.
• 
• To plot the Energy graphs go to, POST > ASCII > LOAD FILE > GLSTAT > SELECT ENERGIES > PLOT > DONE.
• 
• We can see the internal energy increases at the point when the crash box comes in contact with the rigid wall.
• 
• The Kinetic energy reduces on impact with the rigid wall.
• 
• The kinetic energy is converted into internal energy when the box crashes on the rigid wall.
• 
• The nodal acceleration is seen to be less than the Case1. The peak value for this case is 1.6g.
• 

• 

• 

LEARNING OUTCOMES:

• To import the Keyword file.
• To check the model for parts data and keyword manager.
• To assign keywords for the model.
• To define section and material properties for the parts.
• To define rigid wall.
• To define boundary conditions.
• To define initial velocity.
• To define the output results.

CONCLUSION:

By performing this project we conclude that, the complete model setup was done and the model was simulated for crash box for both 1.2mm and 1.5mm thickness.