Week - 4 - crash box simulation

Week 4 – Crash Box simulation

Aim

• Perform a crash box simulation on a rigid wall and find out the difference when thickness of the crash box is changed.

Explanation

• Given is a rectangular cross section crash box with 250 mm length
• Crash box is a passive safety, which helps reduce the impact in case of collision.
• Crash box buckles and folds as it absorbs KE, to aid buckling crash beads are created in the tube.

Procedure

- Open the given mesh model in prepost

- For this analysis we are using a [g mm ms] unit system

- Creation of rigid wall > entity creation >Rigid wall > type planar ; position the rigid wall such that its normal faces in the direction opposite to the velocity

- Assign material to the crash box , steel used a the material in this case

- Assign the section card and give the thickness of 1.2mm for the first case

- Creation of initial velocity > create a set nodes of crash box and assign the initial velocity of -13.889000 mm/ms in negative x direction using the keywords.

- Creation of self-contact for the box because as it crushes (folds), we can prevent penetrations.

- Database cards creation > Cross section set > we get the sectional forces through the box for this we need to create a set of nodes and element set representing the section of the box.

- Create a history node card for getting acceleration values in the crash box

- Binary d3plot and ASCII cards such as GLSTAT, MATSUM, NODOUT, RCFORC, RWFORC, SECFORC, and SLEOUT are created for getting outputs for analysis.

- Control termination with endtim 1ms and control energy card is created computation of Hourglass energy and contact energy

Results

• Verification of Global Energies - we can see the drop in KE as it gets changes to internal energy causing plastic deformation in the crash box.
• The plot of the global energy 1.2 and 1.5mm thick boxes looks very similiar. HG energy is less than 5% for both the cases.

Section Forces

• for 1.2 mm and 1.5 mm crush boxes the max forces through section are 1.66 e+05N and 2.11e+05 N respectively .
• Case 2 with 0.3mm more thickness performs better as it absorbs more force .

Accelerations

• node 3743 is selected and history of the node is requested.
• A peak of 3.66e+03 mm/mm2 of resultant acceleration value is achieved by the 1.2mm thick crush box
• A peak of 3.61e+03 mm/mm2 of resultant acceleration value is achieved by the 1.5mm thick crush box

Effective Stress

• Maximum stress of 354.407 MPa is observed at the element 9523 of the 1.2mm thick tube and has undergone plastic deformation yield limit is 310MPa
• For the second case with 1.5mm thick plate , we can observe 354.371 MPa at the same element id .

1.5mm

Plastic Strain

• 1.2mm tube has a max plastic strain value of 0.021002 at the element 9523 and 1.5mm has strain of 0.0212256

1.2mm

1.5mm

Conclusion

- The simulation of a crash tube was done and obsevation is that the crush box bounces back of the rigid wall.

- The crush tube under goes plastic deformation as it absorbs the incoming KE.

- The animation gifs and drive link - https://drive.google.com/file/d/17BDdZYG4SknJTbJQvCAICGGIw9KrCwda/view?usp=sharing