Learning Forum

[Mert41]

Dear All Experts;

I have examined a welding analysis. I used Goldak's Double Ellipsoidal model in APDL for moving heat source in transient thermal analysis.

I imported the loads obtained in thermal analysis to structural analysis.

I divided the weld line with 10 parts, the length of part 100 mm, the speed of welding is 10 mm/sec. also the weld line was divided 10 parts every divided part's length is 10 mm. in the beginning all the parts are death and for every 1 sec I activated parts respectively.

My question is that when I compare the resulşt between structural analysis which was made with element birth/death texhnique and structural analysis without using element birth and death techique for the same imported loads there is a big difference.

I obtained 200 Mpa values with the structural analysis which is executed without using birth/dead technique and I obtained too much values like 1900 Mpa values with the structural analysis which is executed with using birth/death technique?,

Why do I obtain these different values with these structural analysis which the same boundary condition are used.

I did not use element birth and death technique for transient thermal analysis.

I thank you in advice.

 

Best regards...

[Bill Bulat]

I'm sorry but I'm having a little trouble visualizing the details of what you've done from the explanation you provided. Presumably you're using element birth and death in the structural calculation to mimic the addition of filler metal (e.g., from a weld rod)? Are you able to ascertain (from post processing) if the temperature calculated from your transient thermal analysis is successfully applied to the structural elements when they are activated with EALIVE? I'm quite certain that body loads such as temperatures are zeroed out when elements are EKILLed. If, for some reason, the temperature body loads are not assigned to the elements once they are activated, then large differences in thermal strain will be seen at the interface between elements that were once "dead" and have been activated and those adjacent to them that have been active all along. That's one thing you might check in post processing... created plots of the thermal strain. Presumably your metal has some strongly temperature dependent material properties around the solidus temperature, so that very hot elements are also very soft (like a liquid). My guess is you're also including a material nonlinearity (plasticity).

I would be tempted to try simulating a weld operation with a Transient Coupled Field analysis system. Coupled field elements support birth and death. Then you could activate filler metal elements in the simulation just as they are added in real life (both thermally and structurally). It would probably take a command object to set this up. I guess this is arc welding? Then you could add electric boundary conditions to newly added filler metal elements as they are deposited to include the effect of Joule heating.

You might look at Solution 2055013 to see if it helps:

[Mert41]

Dear Mr. Bulat;

thank you for your comments.

Yes I will try to use element birth and death technique to simulate the addition of filler metal to parent metal. 

I did not use Element Birth and Death technique in transient thermal analysis only I used it for structural analysis.

welding process is arc welding.

I will examine the solution 2055013.

best regards.