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Stress Concentration using USDFLD subroutine

Stress Concentration using USDFLD subroutine

Stress Concentration using USDFLD subroutine

(OP)
Hello everyone

I am using USDLFD subroutine in FORTRAN to model a component with 2 materials and smooth transition btwn both.
I based my work on the functionally graded structure and volume fraction. I used a sigmoid law in order to have a continous transition btw both materials.

I subdivided my problem in the regions like in the picture:


My goal is to reduce the stress concentration of this model:


The stress concentration for a material with E=375GPa is:


So i want to put a material with E=72GPa on the left and make a smooth transition to E=375GPa (to the right) In order to reduce stress on the hole. I used USDFLD subroutine with a if loop to assign different function to the FV depending on the position of the integration points.




So I intend to obtain smaller value than the one material case. But instead of that I always get a stress pick concentration for z=Zi as shown in the plot:


I always saw that an exponential law was used for FGM modeling, this does not required if loop but it is not possible to really control material distribution with it. I found that sigmoid la was more precise but it's like if I had discontinuities in the stress.

Do you think it is because of the condition in the if loop?

Thx

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