Assignment 5

Assignment 5 – Meshing a Bumper Assembly and Simulating a Crash Tube with different notches.

Objective – Comparison of different crash tube behaviours by changing its notches, contact interfaces

Drive Link - https://drive.google.com/file/d/1eRDBL2Mqf9pWjNnVpcSF9sJSvEyFIxm-/view?usp=sharing

Bumper Assembly Meshing

• Open the model in Hypermesh
• Given mesh size is 6.
• Automesh is done on the bumper beams and crashbox
• Seam weld is done wherever necessary on the model.
• Mesh flow was maintained, dependency, equivalence were checked.

Comparison of the crash tube

• Case 1 - Run the crash tube model as it is.
• Case 2 - Change the Inacti=6 and run.
• Case 3 - Create the type 11 contact and run.
• Case 4 - Remove both notches and remove boundary condition on rigid body node then run.
• Case 5 - Create a new notch in the middle, select the whole section and run.
• Case 6 - Create a new notch with nodes only from opposing 2 faces and run.

Case 1

• The given model has type 7 contact interface defined with recommended propteries.( variable stiffness , node to surface contact)
• Image of type 7

• Model is Run in radioss and results are plotted in Hyperview and Hypergraph 2d (Check for energy and mass error)
• Animation plot of von mises, energy plots
• Internal energy increase linearly as the gets crushed due to velocity of 13.3 mm/ms. And reached a max value at 26.8ms, at the same time we can see KE decreasing.
• Rigid wall total resultant forces reached max value at 26.6ms.

Case 2

• Change Inacti = 6 in hypercrash.

• The initial penetration, P0 should be smaller than 30% of the initial gap to avoid contact stability issues. Inacti helps to solve this issue (The gaps are reduced and scaled)
• Run the model in radioss and check for errors.
• Animation and plots
• Contact forces reaches max value of 93N
• IE and KE, Rigid wall force plots are similar to that in case 1.

Case 3

• Create the type 11 contact in hypercrash - This interface simulates impact between edge to Edge or lines.

• There are situations where the Type 7 node to surface interface will not detect the contact due to edges crossing each other at angles. Type 11 interface can be added to capture the physics correctly.
• Contact forces in this case have been reduced to 74N in this case.
• IE reaches a max value of 42272 mJ at 26.8ms and Max rigid wall forces reaches max value at 1363.9N at 26.7ms.

Case 4

• Remove both notches and remove boundary condition on rigid body node.

• Contact forces is reduced to 56.9 N
• IE reaches max value of 42822mJ at 27.6 ms, this is slightly more in value than in case 3 and the max IE reaches almost 1ms later. (due to lack of notches)
• Rigid wall forces reaches max value of 1215.43N at 27.4 ms again almost 1ms later.

Case 5

• Create a new notch in the middle, select the whole section and run. This done in hypermesh using translate and align node.

• Max contact forces have risen to 139 N.
• IE reaches max value of 42469.8 mJ at 27.7ms and Rigid wall forces reaches max of 1231N at 27.5ms

Case 6

• Create a new notch with nodes only from opposing 2 faces and run.

• Contact forces reaches max value of 80.9N
• IE reaches max value of 42386.3 mJ at 27.2 ms and Rigid wall forces reaches 1341.18N at 27ms

Results and conclusion

• Hourglass energy remained almost zero during all the cases
• The presence of notches helps in absorption of more forces into the tubes as it can be observed from cases 4 and 5.
• Max IE remined almost same during all the cases.