Week - 4 - Crash Box Simulation

 

Aim: To do a complete simulation for crash analysis of box having two different thickness of 1.2 mm and 1.5 mm from the given FE model of crashbox.

Objectives-

• Input. k file and output files (D3PLOT, GLSTAT, SLEOUT, RCFORC)
• Animation of the final simulation
• Cross-sectional force generated in the middle of the crash box (along its length)
• Acceleration plot of a node in the middle of the crash box (along its length)
• Maximum directional stress and strain along the length of the crash box (X strain, Y strain etc.)
• Plot of all energies (total, internal, kinetic, hourglass, sliding)
• Compare the accelerations and stress/strain plots of 1.2/1.5mm crash boxes.

 

Procedure-

• We have to open the given LS-Dyna keyword (.k file) file in LS-PrePost, using option File>Open>LS-Dyna Keyword File as shown in below snap.

• Now as we can see from above snap that the model has no input so we have to give the inputs now.
• First we will start with section card, to create section card from keyword>>all>>section>>shell>>here we will input id, elform type and thickness as shown below,

• now we have to create the material card, for creating go to keyword>>all>>mat>>024 linear plasticity and now will input all material properties.

• Hourglass can be defined using HGID. This keyword is used to reduce or control hourglass energy during the simulation.
• Go to Keyword Manager and select the values as shown below.

• Now we have to assign above created properties to part id.

• Now we have to create the contact for the for the box, AUTOMATIC_SINGLE_SURFACE contact with coefficient of friction 0.2as shown below.

• Now we will create the boundary conditions for crash box for intial velocity as 50kmph which is equal to 13.89mm/ms.

• Rigid walls mimic surfaces or volumes that are frequently used to represent stiffer structures that are either stationary or in motion.
• A stationary planar rigid wall is created ahead of the frontal portion of the crash box by selecting a node on the edge, Select planar option and Geo-Vector >> 1n+NL
• Now translate the rigid wall to some distance in the direction of the velocity of crash box.
• The rigid wall is created at a distance of 20mm away from the crash box.

• Now we will define CONTROL_ENERGY card for energy dissipation as shown below.

• Finally we will define the termination time of the simulation which is necessary to run the simulation. The termination time is given as 3 ms in CONTROL SIMULATION Keyword as shown below.

• Now we have to create section for getting section for getting cross sectional forces.
• Cross-section can be created under DATA BASE keyword to measure all cross sectional forces.
• Usually, two rows of elements are selected as a section or a simple plane creation can also be done.

• Now the requested outputs are d3plot, history node and ASCII options are
• GLSTAT: Global Data
• SLEOUT: Sliding Interface Energies
• RCFORC: Resultant Interface Forces
• SECFORC: Cross Section Forces data

• Now we have to check the model from model checker.

• Since there are no errors, we can run the simulation.
• Now we will save the keyword file now and run the simulation using LS-run.

• Both simulations ended with Normal Termination. Therefore, all the models are simulated successfully.
• Now we can open this files one by one using LS-post processor.

Results & Plots-

Stresses-Effective Stress (V-M), X-stress, Y-stress

1. 1.2mm thickness-

2. 1.5mm thickness-

Effective plastic Strain-

1. 1.2mm thickness-

2. 1.5mm thickness-

Resultant Sectional force-

1. 1.2mm thickness-

2. 1.5mm thickness-

Acceleration plot of a node  in the middle of the crashbox (along its length)-

1. 1.2mm Thickness-

2. 1.5mm Thickness-

Maximum directional stress and strain along the length of the crashbox

X-stress-

1. 1.2mm Thickness-

2. 1.5mm Thickness-

Y-stress-

1. 1.2mm Thickness-

2. 1.5mm Thickness-

Plot of all energies (total, internal, kinetic, hourglass, sliding)

1. 1.2mm Thickness-

2. 1.5mm Thickness-

 

 Conclusion:

• The solver deck was set-up for the crash simulation and the required results were requested using the appropriate *DATABASE keyword cards.
• The analysis ran successfully. Post-processing of the results was done using the D3plots and the other output ASCII result files, to produce the deliverables.
• The keywords necessary to build the crash box analysis was created from scratch.
• The model was solved successfully and the results are compared for both 1.2 mm and 1.5 mm thick crash box.
• The results of 1.5 mm crash box showed higher energy absorbing capacity and less deformation compared to 1.2 mm thick crash
• Learned to build a solver deck for simple crash analysis in LS-Dyna and extract the outputs to interpret and compare the results.