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Forming Limit Diagrams in ABAQUS

Forming Limit Diagrams in ABAQUS

Forming Limit Diagrams in ABAQUS

(OP)
Hi there,

I'm a new user and I've decided to subscribe here because I need a help; I'm a mechanical engineer and I'm working on sheet metal forming, in particular hydroforming of aluminium sheet.
I'm actually building up the numerical model in ABAQUS (v.6.10), and I want to insert within the simulation the forming limit diagrams of the aluminium; the strains composing the FLDs come from experimental test performed in a laboratory, so all those values are right.
The initial model didn't have the FLDs implemented within the property module; in order to determine the fracture, I used to export the major and minor strain, to combine one with the other obtaining a strain path for a single node and then I compared the FLD with the strain path superimposed on the same graph; if the strain path intersects the FLD, the fracture occurs, otherwise no fracture happens.
In order to obtain a more global model, I tried to implement the FLD within the model itself; I followed the "trial-and-error" phylosophy and, at the end, I've modified my model in this way:
1- Property module -> I've inserted the option "Damage for Ductile Metals" and in particular "FLD Damage"
2- Step Module -> New Field Output, Failure/Fracture DMICRT (only applied on the sheet)
-> New History Output, Failure/Fracture - DMICRT - FLDCRT (only applied on the sheet)
In this way, on the Visualization Module I can plot the FLDCRT so I can understand if and where fracture occurs.
The question is: for a fixed simulation at a fixed node, I obtain no fracture if I evaluate the FLDCRT (the value is minor than 1), but if I determine the strain path of the same node and I superimpose it on the FLD I have the intersection between the two curves, so I determine fracture at the same node.
So, how can the same simulation give different results only by changing the output variable?
I really hope you can give me a big help since I've tried to find something around the web, but I haven't find anything interesting.
Thanks to all

Antonio

P.S. I hope I've been clear in explaining my problem; sorry for my english! Thanks again.

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