# Special Issue on Fracture and Fatigue Assessments of Structural Components
## 3 Fatigue  
In this Special Issue, the fatigue phenomenon has been investigated from experimental, numerical, and theoretical points-of-view in different papers [4; 5; 6; 7; 8; 9; 10; 11]. Contributions [4; 5; 6; 7; 8] were focused on the application of advanced analytical or numerical approaches to predict the experimental fatigue strength of laboratory specimens; while, on the other hand, papers [9; 10; 11] were mainly devoted to the fatigue assessment of full-scale, real structures undergoing complex loading conditions. [PERSON] and co-authors [4], have applied a critical plane-based multiaxial fatigue criterion for the fatigue life assessment of Ti-6 Al-4V notched specimens. The accuracy of the proposed criterion has successfully been evaluated through experimental data available in the literature. In [5], the authors proposed an energy-based approach for the fatigue life estimation of welded joints through thermal-graphic measurement. A model based on intrinsic energy dissipation was applied to high strength steel welded joints showing a good agreement between estimations and experimental results. Paper [6] was devoted to presenting a multiscale fatigue damage evolution model for describing both the mesoscopic voids propagation and fatigue damage evolution process, reflecting the progressive degradation of metal components in the macro-scale. A method of defect classification was employed to implement 3D reconstruction technology based on the micro-computed tomography scanning damage data with FE simulations. The predictions were validated through a comparison with experimental data. The aim of [7] was to characterize the propagation of fatigue cracks using the damage index derived by various acoustic features of ultrasonic guided waves. The method has been validated by monitoring the fatigue crack propagation in a steel plate-like structure. In [8], the authors have formulated a numerical model to simulate the thorough failure process on concrete, ranging from microcracks growth, crack coalescence, macrocrack formation and propagation, to the final rupture. The model has been applied to simulate the fatigue rupture of three-point bending concrete beams, observing a good agreement between numerical results and experimental observations available in literature. Paper [9] focused on the assessment of fatigue life and characterization of the fatigue crack behavior of an aluminum scroll compressor, taking into account both mean stress effects and elastic-plastic behavior of the material. The authors took advantage of both analytical and numerical models. In [10], the authors have investigated the factors inducing fatigue crack initiation from the positioning block weld toe of metro bogie frame, which is the critical safety part of the urban metro vehicle. Metallographic analyses were employed to study the failure modes and fracture characteristics of the weld toe of positioning block. On-track testing was carried out to obtain acceleration and the stress response information of the bogie, and to investigate which factors could be optimized in order to reduce the failure probability. Finally, the aim of [11] was to develop a master-slave model with fluid-thermo-structure interaction for the thermal fatigue life prediction of a thermal barrier coat in a nozzle guide vane. The master-slave model integrates the phenomenological life model, multilinear kinematic hardening model, fully coupling thermal-elastic element model, and volume element intersection mapping algorithm to improve the prediction precision of thermal fatigue life. This research received no external funding. This Special Issue would not have been made possible without the irreplaceable contributions of valuable authors coming from many different countries, hardworking and professional reviewers, and dedicated editorial team of Applied Sciences, an international, peer-reviewed journal that is free for readers embracing all aspects of applied sciences. I would like to take this opportunity to record my sincere gratefulness to all reviewers.