Assignment 5
Questions:
1. Create the mesh for bumper assembly with a reference mesh size of 6mm.
Crash Tube Analysis:
2. Run the crash tube model as it is.
3. Change the Inacti=6 and run.
4. Create the type 11 contact and run.
5. Remove both notches and remove boundary condition on rigid body node then run.
6. Create a new notch in the middle, select the whole section and run.
7. Create a new notch with nodes only from opposing 2 faces and run.
Solution:
1. Bumper Assembly Mesh Generation
Figure-1 illustrates the overview of the bumper mesh assembly considered for the meshing operation.
Figure-2 illustrates the redundant edge entities that were deleted.
Figure-3a illustrates the overview of the upper crash box of the bumper beam assembly. Figure-3b illustrate the topology error that was corrected before the meshing operation. To fix the error, the separated points were projected onto the main body using the project point tool and the original and the projected points for both the bodies (with error) were merged using replace point command. Figure-3c illustrates the meshed upper crash box geometry using the recommended mesh criteria.
| (a) | (b) | (c) |
Figure-4a illustrates the overview of the lower crash box of the bumper beam assembly. Figure-4b illustrate the topology error that was corrected before the meshing operation. The topology errors were fixed using similar geometric operations as above. Figure-4c illustrates the meshed lower crash box geometry using the recommended mesh criteria.
| (a) | (b) | (c) |
Figure-5a illustrates the overview of the top, middle and bottom bumper beam sections. Figure-5b illustrates the meshed lower crash box geometry using the recommended mesh criteria.
| (a) | (b) |
Figure-6a illustrates the overview of the front and the rear bumper sections. Figure-6b illustrates the meshed front snd rear bumper sections using the recommended mesh criteria.
| (a) | (b) |
Figure-7 illustrates the meshed bumper assembly.
Crash Tube Analysis
The file CrushTube0000.rad was imported into hypercrash. The Unsupported card ALTDOGTAG was deleted. The models were modified according to the problem statement and six unique models were generated and solved using Radioss solver. The discussion for the results including the variation of von-misses stress, rigid wall forces, contact forces, internal and kinetic energy for all six iterations have been discussed below.
1. Variation of Von-Misses Stress
| Iteration No. | Von-Misses Stress Variation | Comments |
| Iteration 1 | Default model. The crumpling of the crash beam initiates at the middle followed by the bottom and the top. | |
|
Iteration 2 (Inacti=6) |
Inacti is set to 6 such that the gap is variable and but the initial gap is adjusted. The deformation mechanism of the crash beam is identical to Iteration 1. | |
|
Iteration 3 (Type 11) |
Type 11 edge to edge contact is added. The deformation mechanism is again identical to Iteration 1. | |
|
Iteration 4 (Removed Notches and BC's) |
The notched are removed. The boundary condition on the rigid node is removed. In regards to the deformation mechanism, the crumpling starts at the bottom and propagates to the top of the crash beam. | |
| Iteration 5 (Notch in Middle) | The original notch is removed and a notch around the middle of the beam of depth 2mm is introduced. The crumpling starts at the middle, propagates to the bottom of the crash beam and then to the top. | |
| Iteration 6 (Notch on opposing Faces) | The notches on two opposing faces are removed from the model in Iteration 6. The crumpling starts in the middle at the notches and propagates around the beam. |
2. Variation of Rigid Body Forces
Figure-8 illustrates the variation of rigid body forces in the Z-Normal direction for all six models. It is observed that changing the Inacti value to 6 did not have any effect on the normal rigid body reaction force in Iteration 2. Hence, the curves for Iteration 1 and 2 overlap over each other. Similarly, adding type 11 contact in the model in iteration 3 did not have any effect on the normal rigid body force. Hence, the curve overlaps over the curve for Iteration 1 and 2.
Comparing the performance of the three notch designs, the model in Iteration 5 has the highest normal rigid body force followed by Iteration 6 and Iteration 4, respectively. Hence, the model in Iteration 5 and 4 will have the higher and the lowest rebound acceleration/force, respectively.
3. Variation of Contact Energy
Figure-9 illustrates the variation of contact energy for all six iterations. The general behaviour remains very similar for the six cases with only notable changes observed in the period of 20 ms to 30 ms. The energy dissipated by contact for Iteration 1 and 2 remains identical, with iteration 3 having higher energy due to inclusion of the Type 11 edge to edge contact.
Out of the three notch designs, the notch in Iteration 6 has the highest contact energy followed by the model in Iteration 5 and Iteration 4 respectively.
4. Variation of Internal Energy
Figure-10 illustrate the variation of the internal energy for all six models. It is observed that the variation of the internal energy is absent for the models in the first three iterations.
Comparing the performance of the three notch design, it is observed that the model in Iteration 4 has the highest internal energy followed by Iteration 5 and 6 respectively up to a period of 22 ms. Beyond 22 ms, the internal energy for the model's Iteration 4,5 and 6 remain indistinguishable.
Conclusions
The mesh for the crash bumper model is successfully generated.
The six models of the crash beam model have been successfully studied.