Simple procedure to perform limit load and elastic-plastic analysis

[Mm.Kaiser]

Dear friends,
I use elastic stress method to perform finite element analysis with Ansys (calculating mem and bending stresses) but i want to use limit load and elastic-plastic analysis too.
I read asme2 part5 more and more but i have a lot of doubt in my knowledge for these methods.
Can anyone tell me step by step simple procedure to perform these methods with Ansys?
(Note that i want to analyze 3D assembly of quick opening closure made from linear elastic steel that have some frictional contacts)
Thanks a lot

 

[TGS4]

This is not an analysis that you want to try as a start to elastic-plastic analysis. The contact aspects make for very "interesting" aspects for an elastic-plastic analysis. I will give you the same advice that I have dished out repeated on eng-tips: either get a mentor or hire a very experienced and skilled consultant to "teach" you.

As a first question: do you understand what is meant by all of the various failure modes described in Part 5? Have you purchased and reviewed ASME PTB-1?

 

[Mm.Kaiser]

Dear TGS4,

I didn't bye that mentioned book and just read the ordinary standard and use my fundamental science of engineering to understand what that means. so it is possible that i didn't understand the exact concept of failure modes. It is why that i asked you in this post.

I have worked in pressure vessel field since 8 years ago and a lots of my designs according to elastic analysis were working well in industries without any problems.
But some client technicians ask me why don't you use limit load and elastic-plastic method whereas your stresses in some zones are higher than yield strength and i can't satisfy them.

what do you mean for this sentence: "The contact aspects make for very "interesting" aspects for an elastic-plastic analysis". i can't understand!

thanks for your challenging notes!

 

[TGS4]

You REALLY need to get PTB-1. You also REALLY need to understand what is meant by "Protection Against Failure Modes". In my opinion, unless you truly understand failure modes, whatever you do with respect to design-by-analysis is just punching numbers into a computer program.

Do yourself a favour, and do some research (starting with PTB-1) into failure modes: Plastic Collapse, Local Failure, Buckling, Fatigue, and Ratcheting. Once you have a good grasp of that, then do some research into LFRD (Load Factor and Resistance Design). Understand the concept of factored loads, and their relationship to design margins. Finally, relate this back to the failure modes, so that you understand the design margins that are inherent in the Code.

Finally, once you understand factored load design, you will understand why designing for contact using a factored load approach is "complicated".