Setting up a crash simulation in LS-Dyna
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This document provides steps to set up a crash simulation in LS-Dyna of an aluminum rail crashing into a rigid wall. It describes importing the rail model, defining the wall, applying mass to one end of the rail, assigning material properties of aluminum to the rail, applying an initial velocity to the rail, setting the simulation time and output steps, defining a special node for high resolution output, and configuring the simulation to output force on the wall, material data and displacement of the special node. Running the simulation would show the crash results and special outputs in the LS-Dyna software.
![Material Properties
Density
[kg/𝒎𝒎 𝟑]
Youngs Modulus
[GPa]
Yield Stress
[GPa]
Tangent Modulus
(ETAN)
Poisson
Ratio
Aluminum 2.7 x 10−6
70 0.20 2.00 0.33](https://image.slidesharecdn.com/settingupacrashsimulationinls-dyna-180313034726/85/Setting-up-a-crash-simulation-in-LS-Dyna-3-320.jpg)
Setting up a crash simulation in LS-Dyna
- 1. Setting Up a Crash Simulation in LS-Dyna Made By: Akshay Mistri
- 2. Scenario under Consideration • Given Aluminium rail needs to be crushed against a rigid (non-deforming) wall. • Velocity of rail is 15.6 mm/milli-sec. • 500 KG mass is distributed on the non-impacting end.
- 3. Material Properties Density [kg/𝒎𝒎 𝟑] Youngs Modulus [GPa] Yield Stress [GPa] Tangent Modulus (ETAN) Poisson Ratio Aluminum 2.7 x 10−6 70 0.20 2.00 0.33
- 4. Importing the Rail into LS-Dyna • Go to file > open > Keyword file. • Browse your file (should be a .k file). • You would see your rail imported into the LS-Dyna software.
- 5. Adding a Wall • Go to page 5 > Wall > Create > Planar. • Select the normal vector for the wall. (NormX here, refer picture below.) • Click in the box under Tail, against X. (refer picture below.) • Then click on the last corner node on the impacting end. • As you click on the node, you would see some values entered in the Tail and Head columns. • Currently, the wall is coinciding with the corner node. • Click on the first box under Tail and enter -1, hit enter key. (Click on NormY option and again click on NormX option to refresh the position of the wall.) • This will shift the wall behind by 1 mm. • Click on apply and then on done.
- 6. Wall Normal Vector • The normal vector of the wall should be against (opposite) to the motion of the wall. • To check that, go to Page 5 >Wall > Modify > Click on the Wall name PLANAR. • You can see the blue arrow pointing in the direction opposite to the motion of the rail. • This will ensure that the rail elements would see the wall (take contact).
- 7. Adding Mass • Go to page 5 > MassD > Create. • Click on the “Top” button provided in the bottom area. (refer picture below) • Click on the “Area” option. (refer picture below) • Now drag and select the end nodes of the non impacting end. • This would select all the nodes in the cross section. • Now add mass value (per node mass, 500KG/80 = 6.25 here). • Click on apply.
- 8. Describing Material • Go to Page 3 > *MAT > Select 024 Piecewise_Linear_Plasticity. • Click on edit. • Click on the NewID > Enter Title. • Enter the Material Properties. • RO = Density • E = Youngs Modulus • PR = Poisson Ratio • SIGY = Yield Strength • ETAN = Tangent Modulus • Click on Accept > Done
- 9. Describing Property • Go to Page 3 > *Section > SHELL. • Click on edit > NewID. • Enter thickness in T1 and hit enter. (3 mm here)
- 10. Assigning Material & Property to the Rail • Go to Page 5 > PartD > Assi (Assign). • Select the rail (the only part we have). • Click on SECID and choose the section we created. (refer picture below.) • Similarly, select the MID (Material ID). • Click on Apply.
- 11. Assigning Velocity • Go to *Initial > Velocity. • Click on edit. • Put NSID = 0. • This would assign velocity to all the nodes. • Give velocity in VX = -15.6 mm/msec.
- 12. Simulation Time • We need to provide the time for which the program will simulate the scenario. • Go to page 3 > *Control > Edit. • Provide 50 m-sec in ENDTIM. • Analysis will be simulated for 50 milli-seconds.
- 13. Simulation Steps • Also, we need to provide the steps in which the calculation will be done. • Go to page 3 > *Dbase > BINARY_D3PLOT. • Here we provide the value of DT to be 2.5 • So, will have results for 𝐸𝑁𝐷𝑇𝐼𝑀 𝐷𝑇 = 50 2.5 = 20 steps. ( at 0, 2.5, 5, 7.5…. Milli-seconds).
- 14. Providing History Node • We can define a node for which the program will make more accurate calculation (not in steps of 2.5 milli- seconds). • For this, go to page 3 > *Dbase > HISTORY_NODE. • Click on ID1 and click on Pick. • Pick a node from the rail displayed on the non-impacting end. Click on Insert. • This is provided to note the displacement of the rail in x- direction. • Nodes on the impacting end will have erratic motion due to crushing, so we select one from the non-impacting end.
- 15. Getting the Results we desire • Also, we need to ask the program the for any special results we want to see. This could include Rigid Wall forces, material summary, more accurate calculation for any special nodes. • For this, go to page 3 > ASCII Option > Edit. • Check mark on MATSUM which will provide the material summary. • Providing value DT = 0.001 will do calculations in 𝐸𝑁𝐷𝑇𝐼𝑀 𝐷𝑇 = 50 0.001 = 50000 steps. (0.001, 0.002, 0.003… milli-seconds) • We will use this value of DT for other result options as well.
- 16. Results for Special Nodes • For the history node we provided in slide 14 (node ID 3128), we can define the more accurate calculation here in ASCII Option. • Scroll down and check mark on NODOUT. • Provide the value of DT to be 0.001. • So, for the node 3128, the calculation will be done in 50000 steps.
- 17. Getting the Rigid Wall Forces • We can also request the Forces generated with time on the rigid wall we made. • For this, check mark on RWFORC and provide the DT value.
- 18. Running the Simulation • We are now ready to provide use this file for analysis. • First, we need to save the keyword file with .k extension. • The keyword file can be run by using LS-Dyna Manager. • We could load the results by going to File > Open > Binary Plots. • After the simulation is completed, we could see the results in page 1 > History.
- 19. Special Results • For the special results, go to page 2 > Binout. • Click on Load (shown below) and load the Binout file. • Click on open files and you would get the special results requested. • MATSUM will give material details. • NODOUT will give results for the special node (3128). • RWFORC will provide rigid wall forces.
- 20. Thank you!