Fatigue assessment and plasticity

[corus]

In reviewing results from an elastic-plastic model where stresses are limited by the yield criteria, is there a method or software available by which the fatigue life of the welds can be determined when plastic strains are determined for each cycle? All the codes appear to refer to elastic analyses, usually determined by 'engineering' calculations. The results were obtained by Abaqus.

 

[tld23]

Corus,
There are many of methods than can be used, at the extremes there are:
1) The psudo-elastic stress range method. Just use the strain range multiplied by the elastic modulus and then use this along with traditional S-N curves. Not very secentific but it does work (for steels at least).
2) The local stress-strain method; look this up in any reasonably advanced fatigue text book.

As far as software goes the main company working in this area is Ncode (

http://www.ncode.com/).

TERRY

 

[PVI]

Corus,

both linear and pseudo-elastic calculations can be used to perform fatigue calculations. Neuber correction is aimed at correlating your linear stresses or deformations with the cyclic stress-strain curve. if you have performed your calculations using Abaqus (pseudo-elastic model) you normally have the true strain and stress tensors, thus no need for performing corrections. As soon as local plasticity occurs, the local deformation approach must be used rather than the S-N one.
Welds are different issues since they might be classified first since they do not exhibit same kts or kfs, unless LBF method is used

Ph.V