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FEMFAT plast

This module is for calculating elasto-plastic stresses based on a linear elastic FE analysis.

FEMFAT plast makes use of the Neuber correction to estimate the local elasto-plastic stresses in notches on the basis of linear-elastic stresses.

For this application, the Neuber rule establishes a relationship between linear and non-linear stresses or strains. With the Young's Modulus and the non-linear strains, this relationship (“Neuber hyperbola”) can be written as

Making use of the Ramberg-Osgood equation for describing the cyclical stress-strain curve (with the cyclical coefficient and cyclical exponent of hardening), it is possible to calculate the non-linear stresses as 

the intersection with the Neuber hyperbola.

Consequently, with local plastification, no FE analysis with non-linear material behavior is necessary; the elasto-plastic stresses can also be determined with FEMFAT plast by approximation. This also entails a calculation effort that is reduced accordingly in the FE analysis.

FEMFAT plast is available as an influence factor for BASIC and MAX and is activated by default.