Explicit analysis results and location differ according to mesh size

[Hkn88]

Hello gents,

I have run Explicit analysis simulating drop test. I used hex dominant method(mostly) to mesh and ran mesh refinement process to validate the results.

Looking at the critical surface which hits to the ground i observed the highest stress values. Notewithstanding during decreasing mesh size from 8 mm downwards results have converged to a value, i examined results and saw max value location change from analysis to analysis(I pointed out the locations from the same view, attached). By the way, max value are also changing in terms of time(5 mm analysis show max value at 1,95 e-3 sec, however 4 mm shows 2,05 e-3 sec)

My question to experienced users:
1. Is watching max stress value(averaged) in the critical place correct method for convergence analysis? Or shall i watch strain or stress(Nodal fraction) instead?
2. Is it correct to expect the max value to converge in the same location during mesh refinement?
3. Is it normal to observe max value results at different time during mesh refinement?
4. Is none of above items are meaningul, what is the correct way for making convergence analysis for explicit analysis?

Thanks.

 

[L_K]

I assume running an explicit analysis, you have already checked that energies are conserved in the system.
In my opinion, to study mesh refinement, it would be best to pick one location and one time. Stress
value should converge.