Nonlinear analysis of stress concentrations in creep realm
Nonlinear analysis of stress concentrations in creep realm
(OP)
I am running a nonlinear analysis of a stainless steel structure at 1450 F, and need some guidance (I am new to nonlinear FEA). The design is governed by the ASME allowable stress which is lower than the yield stress; so my stress concentrations after the nonlinear analysis are lower than the yield but are higher than the allowable. How do I interpret these results? Are these areas susceptible to creep failure or will creep act as yielding and redistribute the loads?





RE: Nonlinear analysis of stress concentrations in creep realm
In the creep regime, I would not ignore creep effects, particularly for longer time periods (>100 hours).
RE: Nonlinear analysis of stress concentrations in creep realm
RE: Nonlinear analysis of stress concentrations in creep realm
RE: Nonlinear analysis of stress concentrations in creep realm
RE: Nonlinear analysis of stress concentrations in creep realm
RE: Nonlinear analysis of stress concentrations in creep realm
RE: Nonlinear analysis of stress concentrations in creep realm
RE: Nonlinear analysis of stress concentrations in creep realm
Are the stress allowables applicable for stress results from an elastic - plastic analysis?
Regarding stress concentrations, remember that with an elastic plastic analysis, stress concentration goes down in the plastic regime but strain concentration should increase. You need a rigorous model of the notch to address plastic strain concentration. Initiation of rupture will be due to the concentrated plastic strain whether its fatigue or creep.
RE: Nonlinear analysis of stress concentrations in creep realm
After thinking more about this, I do not think that they are. I think I need to do Viscoplastic analysis, but I do not know where to get those properties from. It seems very hard to find material properties at elevated temperatures.
"Initiation of rupture will be due to the concentrated plastic strain whether its fatigue or creep."
Does this cause crack propagation which migrates out of the concentration?
RE: Nonlinear analysis of stress concentrations in creep realm
Creep cracking will propagate only is the material toughness is less than the stress intensity caused by the cracking. As you are operating at a very hot temperature, toughness is probably sufficient to resist crack propagation unless you have material embrittlement.
RE: Nonlinear analysis of stress concentrations in creep realm
Furthermore, creep cracking is a different failure mode than cracking otherwise. Creep fracture will initiate and propagate based on creep damage. It not really a factor of the toughness.
RE: Nonlinear analysis of stress concentrations in creep realm
RE: Nonlinear analysis of stress concentrations in creep realm
TGS4 is correct in the comment about creep fracture propagating based on creep damage, however, when the extent of creep damage is localized to a hot spot, further propagation depends upon the fracture toughness of the material (or possibly other damage such as fatigue). Both API 579/ASME FSS-1 and PD7910 give methods for handling all.