Friday, January 6, 2012
Fatigue of structures: basic concepts, cyclic behavior, numerical procedures and lifetime models
Mahaman Habibou Maitournam, Professor, Ecole Polytechnique
The fatigue failure is a major concern of all the engineering industries, as many (sometimes tragic) accidents are due to misunderstanding of the problem. The lifetimes of micro-systems as well as macro-structures are often shortened by fatigue. The development of a theoretical method for the estimation of fatigue resistance is therefore of paramount importance. In this talk, some examples of fatigue problem coming from the automotive, aerospace and railways industries are given to simply explain the complexity of fatigue design. The different types of fatigue from low to high cycle are defined in connection with the dissipated energy in the asymptotic regime (elastic shakedown, plastic shakedown or ratcheting) under cyclic loading. Then a comprehensive approach of fatigue is presented; it is based on the following ingredients: (i) Constitutive modeling to account for the cyclic behavior which may presents hardening or softening; (ii) Numerical strategies for the determination of the asymptotic state under cyclic loading; the aim is to directly determine this steady state without the simulation of all the transient cycles; (ii) Thermo-mechanical fatigue life models for macroscopic dissipative and non dissipative structure under multi-axial and thermomechanical loading.