FEA Analysis Ductile and Brittle Fracture of Steel

[MakeItSo]

Hello,
I am modelling a piece of steel (typical structural steel) that will be heavily loaded in a variety of directions. I am using FEA to check the stress distribution of the part. I am checking Von Mises criteria for yielding, as compared to the yield stress as determined from a typical steel tensile coupon. Due to the complex nature of the loading, I would also like to check for the potential of brittle fracture due to high principle stress (even if there is no yielding). What value should I compare the max. principle stress to? The ultimate stress of a steel coupon? Is it possible to achieve brittle fracture in what is typically considered a "ductile" material?
Thanks.
J

 

[FEA way]

For brittle fracture there are other criteria to be used rather than principal stress. So called J integral is the most important one. In case of Linear Elastic Fracture Mechanics there are also stress intensity factors K for three possible crack modes. These are related to J integral and can be compared with critical value - Kc (fracture toughness). There are also energetic criteria - energy release rate G (= J) and its critical value Gc. For nonlinear analysis J integral can be used too but there’s another, two-parameter approach with so called T stress.

 

[rb1957]

"Is it possible to achieve brittle fracture in what is typically considered a "ductile" material?"

if the specimen is cooled below the embrittlement temp,

if the specimen is compromised by a large flaw or several small ones,

if the specimen is compromised by corrosion,

...

is the loaded structure a panel/web (ie a 2D element) or an axial (1D) element ?

why wouldn't you use max principal compared to Ftu ?

another day in paradise, or is paradise one day closer ?