A multiaxial fatigue approach based on damage mechanics

Among the methods proposed to study the fatigue assessment of structural components under a complex multiaxial stress history, those based on damage mechanics concept represent a mechanically-based approach that can be easily applied in fatigue design of structural components. In the present paper, a model for fatigue damage evaluation in the case of an uniaxial or arbitrary multiaxial loading history is proposed by using an endurance function which allows us to evaluate the damage accumulation up to the final failure of the material. By introducing an evolution equation for the endurance function, the final collapse of the material can be assumed to occur when the damage is complete, i.e. when it reaches the unity value. The parameters of the proposed model, which uses the stress and deviatoric stress invariants to quantify the damaging phenomenon, are determined through a Genetic Algorithm once the fatigue behaviour for few complex stress histories is known for the material under study. The proposed model presents the advantage to not require any evaluation of a critical plane and avoid the necessity of any cyclic counting algorithm to quantify the fatigue life, since it considers the progressive damage process during the fatigue load history.