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Full and sectioned (symmetry) static analysis give different stress results

Question asked by Mladen Pavlovic on Sep 11, 2015
Latest reply on Nov 3, 2015 by Jim Riddell



i have a simple pipe with flange on its end which i wanted to analyze. I wanted to compare the analysis of full part and sectioned part using symmetry fixture. What i got were 2 completely different results.


For analysis i applied forces in all three normal directions as well as torque in all 3 planes (simulating nozzle loads for pressure vessel calculations) on one end of the assembly. The other side, which also has a flange was fixed.


"full" assembly gave me max stress at ~ 2,300 psi,




then i split the pipe in half to speed up the simulation and i got completely different result. I applied symmetry fixture on all planes that were formed with my cut extrude feature. Stress was concentrated in one area and it was ~7,000 psi. About 3.5 times greater than in "full" pipe analysis. It seems that symmetry was not taken into account. When selection symmetry fixture, it did create symmetric outline of the assembly and i was able to create a plot to include symmetric results. Stress concentration at the cut surfaces is expected if the pipe is actually cut in half, which obviously is not the goal here.





I have bonded connection on all parts. Multi-body assembly analysis was preformed. All parameters stayed the same - Mesh, Fixtures , Forces. The only thing i noticed it was different is that at some point, during sectional simulation, it gave me warning that more accurate surface-to-surface bonding is used , while on a full pipe, it was simplified. Now when i run it it uses more accurate option for both options..




Any help in showing me where i am making mistake(s) is helpful.


Thank you