Dear Colleagues,

For load conditions relatively far from safe values, fatigue is the most important parameter to be considered in the behavior of mechanical and structural components subjected to constant or variable amplitude loading. Fatigue life is influenced by mechanical, metallurgical, and environmental variables.The purpose of this Special Issue is to evaluate the most recent technological developments regarding knowledge of fatigue life evaluation of steel. The forecast of steel performances is fundamental for the safety, maintenance management, and replacement planning of components of most industrial products and production plants. Furthermore, reliable knowledge of the performance of a product allows designing and carrying out treatments during the production phase that can increase the fatigue lifetime.

The problem of fatigue life prediction concerns both parts under development and already existing parts that have undergone, for example, aging and variations in load conditions.
To carry out a health assessment of old plants or mechanical components, it is necessary to obtain information about the current stress response of structural members. The real loading unloading conditions must be known; however, the typical loading history is often not available. To solve these problems, the most direct way is to take the stress measurement from field tests to increase the reliability of evaluation results.

Among the current fatigue analysis methodologies, the traditional stress–life (S–N) approach has been widely used for fatigue-related design and evaluation the steel structures. When the stress–life approach stipulated in specifications is adopted for steel structure fatigue damage and life evaluation, it is requisite to know the stress spectra of critical locations and the S–N curves of the details.

From a microscopic point of view, fatigue is the process of progressive, localized, and non-recoverable microstructural developments that can lead to final failure of specimens or structures. A typical feature of the microstructural changes during a fatigue process is that a part of the repeated elastic–plastic deformation is dissipated irreversibly as heat. Therefore, the measurement of thermal parameters (the effect of strain gradient on nonlinear kinematic hardening and hysteresis behavior must be considered), local microplasticity, and microstructure evolution may be used to model or predict fatigue properties such as fatigue strength and fatigue life. Microplastic distortions help to estimate the evolution of the material resistance.

In structural engineering applications, nucleation and propagation of fatigue cracks are some of the most important considerations in the mechanical properties of metals. In high-strength steels, surface and subsurface defects play an important role in the reduction of the fatigue limit; therefore, the treatment that induces a compressive state on the surface can increase the fatigue life of the structures.

High flash temperature due to impulsive contacts can cause surface defects, such as cracks, spalling, fatigue, and wear. These defects are correlated with thermomechanical stress and material softening. Since it is difficult to directly measure impulsive contact temperature, analytical and numerical modeling methods must be used as an effective way to solve thermal or thermomechanical contact problems. Therefore, for impulsive contact, the model must be used for both fatigue live evaluation and stress evaluation. The reliability of the models is in this case particularly relevant for the solidity of the final forecast.

This Special Issue focuses on models for fatigue life prediction and evaluation methods for the life evaluation of existing units.

Prof. Andrea Gatto
Guest Editor

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• loading and fatigue
• stress measurement
• fatigue strength
• fatigue life prediction