The evaluation of fatigue damage is crucial in engineering because fatigue is becoming determinant in design in the sense that it is frequently the cause of failure of mechanical components and structural elements. Fatigue failure is the culmination of a progressive process that occurs when a certain damage level has been attained. The speed of the process depends on the microstructural characteristics of the material and increases with the number of cycles, the stress range and the stress level in every cycle, three factors to be taken into account when analyzing damage. Real structures are subjected to complex fatigue load histories involving varying stress ranges and varying stress levels. In contrast, laboratory tests are usually carried out under constant stress range and constant stress level (S-N curves) (see ASTM (1981)) or under a particular accelerated load history (see Sonsino (2007), and Heuler and Klätschke (2005)) with the aim of obtaining basic information on the material. Less often constant strain tests are also performed. Thus, in general, laboratory tests are not intended to reproduce the complex fatigue conditions of the actual structures. There exist a long list of models dealing with the parametric definition of the S-N curves for a constant reference stress level, as for example Coleman (1958a), Bastenaire (1972), Lawless (1982), Spindel and Haibach (1981), Pascual and Meeker (1999), Castillo et al. (2006), etc.), which must be complemented with a damage accumulation model to proceed with the evaluation of fatigue damage and subsequent fatigue life prediction.
KeywordsWeibull Distribution Failure Probability Fatigue Damage Fatigue Failure Crack Size
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