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[Jamil Atileh]

Hello there,
Sorry for the long explanation in advance.
If I can send my ansys file to one of the ansys experts, it would be better to check my work if that is possible, and I'm also going to attach some screenshots of my work.
 
I'm doing nonlinear buckling analysis, and I also want to do the ARC length method to predict post-buckling behavior using the ANSYS 2023 student license for conical tanks I want to use ASYS results to develop a code to predict the minimum wall thickness to avoid buckling and failure. 
I used the design modeler to draw my geometry with 3 different surfaces; each one has a different thickness, and those thicknesses are like this from top to bottom. 
6.4 for the upper part, 8 for the mid part, and 10 for the lower part, and I want to assign steel material for the linear case and bilinear isotropic hardening for the nonlinear case. 
i used two connections to connect those surfaces to each other the bonded type and for mesh i used element size 400 mm also i used mesh size option and i insert node merge option twice to merge all nodes together also i used mesh numbering to make sure do not exceed the limitation for student license which is i think around 3500 nodes in total and i put value of 10 to consider the geometry imperfication and for linear step i turned of large deformation option after that i started to insert my boundray condition which is displacement on the top x=z=0 and y free and i also insert same displacement for bottom edge but in this case i wanna x=y=z=0 and i also have hedrostatic pressure from inside with value for fluid density is 1400 kg/ m^3 and x=z=0 and for y=9.81 m/s^2 at surface y= 9m for surface location and also the standard gravity after that i insert the total deformation and  equivalent stress for static structure and for eigenvalue buckling i insert the total deformation  and i did same steps for nonlinear with turn on large deformation and turn off the line search and stabilization and i assign the bilinear material for this step to the geometry  
I have some questions: 1. When I'm defining the materials, specifically the bilinear case, there is something wired in the stress-strain chart; it should be more than just an inclined line. By the way, I'm going to post photos to make it clear.
2. For my results, it doesn't make sense, especially for convergence,deformation and stress. 
3- For the arc length method, as I saw from the previous discussion here, it's not applicable for this version, and I already watched the video for homework (2) when they explained how we can do the arc length. I tried this way, but I think they used line bodies, and they ended up with code. They wrote it in the command option, but I'm not sure how I can do it for my model. 
Thanks in advance for everything. and I'm looking forward to hearing from you.
Best regards
Jamil Atileh 
 
 1- the chart should be like this 
 

but my chart like this 

2- My results for linear buckling 

eigenvalue total deformation  

static analysis total deformation and stress (von mises)

stress

directional deformation

mesh

boundray conditions

standard earth gravity

hedrostatic pressure

displacement at top and bottom

connections

geometry 

3-for nonlinear analysis

geometry 

anaylsis settings

total deformation

stress

convergence

messages 

geometry imperfecation

 

 

 

 

[Ashish Khemka]

 

Hi Jamil,

I am not completely able to figure out the issue you might be facing but please see if the following post is of help to you: The eigenvalue Buckling Analysis and the nonlinear buckling analysis (ansys.com)

In addition, please see if this blog is of any help to you: Eigenvalue Buckling and Post-buckling Analysis in ANSYS Mechanical - PADT (padtinc.com)

Regards,

Ashish Khemka

 

[Jamil Atileh]

Hi Ashish,
Thanks for your replay. My issue Simply speaking, I'm doing nonlinear buckling analysis, so my results or the curve for the non-linear case are still linear. Even though I tried to reduce the yield strength and increase the scale factor, I'm still getting linear, and the stress should exceed the yield but not become less than before. I'm not sure what the problem is.
I will also attach some screenshots to make my question clear.
One more thing I want to do is use the arc length method. Is there any way to do it using ASYS 2023? What do you advise me to do? 
best regards 
Jamil Atileh

so the curve for non linear case should be like this 

but i got the curve like this