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International Journal of Materials Engineering and Technology

International Journal of Materials Engineering and Technology
Volume 4, Issue 1, Pages 15 - 37 (July 2010)

DAMAGE INCREMENT ACCUMULATION APPROACH FOR MULTIAXIAL FATIGUE LIFE PREDICTION
Roberto Brighenti

Abstract:
The fatigue assessment of structural components under complex multiaxial stress histories in engineering applications is a demanding task, since fatigue damage and failure depend on all the components of the stress tensor and on their variation during the whole fatigue phenomenon. As is well-known, several materials present a so-called fatigue limit under constant amplitude fatigue loading, while in the case of arbitrary varying and/or multiaxial stress histories a fatigue limit cannot be defined in the same way. Among the methods proposed to study this problem, those based on damage mechanics concept represent a mechanically-based approach that can be easily applied in fatigue design assessment of structural components. In the present paper, a model for fatigue damage evaluation applicable to cases of uniaxial or arbitrary multiaxial load histories is proposed by introducing an endurance function which allows us to evaluate the damage accumulation up to the final failure of the material. By defining 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 few uniaxial or complex stress histories, and their effects in term of fatigue life, are known for the material under study. The main advantages of the proposed model are the unnecessary evaluation of any critical plane and any conventional cyclic counting algorithm - as usually required by classical approaches - to quantify the fatigue life; such a simplicity is due to its mechanical-based approach which considers the progressive loading process step by step and its effect in terms of damage increment accumulation.

Keywords and phrases: fatigue life, multiaxial, continuum model, damage, genetic algorithm.

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