Technical background

Multi-FEAST© is designed to estimate fatigue damage under constant and variable amplitude uniaxial and multiaxial fatigue loading using the theories and approaches listed below.

Fatigue damage. Multi-FEAST© estimates fatigue damage by taking full advantage of the Modified Wöhler Curve Method. This multiaxial fatigue method is a bi-parametrical critical plane approach designed to estimate both high-cycle fatigue strength and finite lifetime of engineering materials subjected to in-service multiaxial fatigue loading. The Modified Wöhler Curve Method postulates that, independently from the degree of multiaxiality and non-proportionality of the applied loading path, Stage I fatigue cracks initiate on those material planes experiencing the maximum shear stress amplitude.

Critical plane. The Shear Stress-Maximum Variance Method postulates that the orientation of the critical plane can be determined by locating those material planes containing the direction experiencing the maximum variance of the resolved shear stress. This approach is seen to be very efficient from a computational point of view: as soon as the variance and co-variance terms characterising the load history under investigation are known, the computational time required to reach convergence is not affected by the length of the stress signal being post-processed.

Cycle counting. By post-processing the shear stress resolved along the direction of maximum variance, Multi-FEAST© employs the classical Rain-Flow method to determine shear stress spectra under variable amplitude uniaxial and multiaxial fatigue loading.

Fatigue strength reduction factors. If the fatigue assessment is performed in terms of nominal stresses, Multi-FEAST© takes into account the detrimental effect of notches according to the classic theory as formalised by Peterson.

Point method. According to the Point Method, Multi-FEAST© allows fatigue strength to be estimated by directly post-processing the linear-elastic stress fields damaging the material in the vicinity of a geometrical feature, or notch. In Multi-FEAST©, the Point Method can be applied to both notched and welded components.

Nominal and hot-spot stresses. According to the Recommendations of the International Institute of Welding, Multi-FEAST© can estimate fatigue damage in welded components subjected to both constant or variable amplitude uniaxial and multiaxial fatigue loading by determining the relevant stress states in terms of either nominal or hot-spot stresses.

Reference Radius concept. The most advanced design methodology recommended by the International Institute of Welding is that based on the use of a reference radius, where the profile of either the weld toe or root is rounded with a circular fillet of radius equal to either 1mm or 0.05mm. Multi-FEAST© allows linear-elastic stress states determined according to this concept to be post-processed to estimate fatigue damage under both constant and variable amplitude uniaxial and multiaxial fatigue loading.

Multi-FEAST© can be used to design both structural un-notched/notched and welded components.

Are you interested in the theories which are implemented in Multi-FEAST©? Please, have a look at our reference textbook:Multiaxial Notched Fatigue