Advances in Fracture, Fatigue and Structural Integrity Analyses of Metals

1. Introduction and Scope

Given the good response of the scientific and technical communities to our previous Special Issue in Metals, titled “Fracture, Fatigue and Structural Integrity of Metallic Materials” (2019), and given that research in these fields is continuously increasing in qualitative and quantitative terms, this new Special Issue intends to provide a forum for the dissemination of the latest significant advances in fracture, fatigue and structural integrity analyses.

Fracture, fatigue, creep or environmentally assisted cracking, among other critical and subcritical processes, still present many open issues. The focus of the ongoing research ranges from the very basic aspects explaining the material response at atomic and microstructural scales to the development of engineering procedures defining the structural integrity conditions of a given structural component.

The application of all this newly developed knowledge affects a wide range of sectors where structural safety is a major concern: nuclear power plants, civil engineering structures, oil and gas, pressurized equipment, aircraft, naval structures, etc. Structural failures in any of these sectors may have evident and serious consequences in terms of human lives, environmental disasters or economic losses. Therefore, in order to avoid structural failures, it is necessary to understand the different mechanisms generating critical and subcritical processes in the structural materials and to develop assessment techniques and management procedures for the corresponding structures.

In this context, this Special Issue is focused on the latest advances in fracture, fatigue, environmentally assisted cracking and structural integrity assessments of metallic structural components containing defects (cracks, notches, local thin areas, etc.) and also on developments that are being or could be incorporated in structural integrity assessment procedures.

2. Contributions

Six contributions (four articles, one review and one communication) have been published in this Special Issue. Five of them are related to fatigue: three papers study this phenomenon in industrial components, and two papers explore the interaction between fatigue and the environment. The sixth paper analyzes the effect of residual stresses.

Among the fatigue analyses on industrial components, Woo et al. [1] demonstrate the applicability of parametric accelerated life testing as a procedure to identify design deficiencies in generating a reliable quantitative specification. They used a reliability methodology that included a generalized life-stress model using a linear transport process and a sample size formulation. Finally, they analyzed the failure and redesign of a pneumatic cylinder as a test case for the methodology. Yin et al. [2] provide a review of rolling-contact-fatigue-related microstructural alterations in bearing steels, raising key questions and paradoxes regarding each type of microstructural feature and suggesting possible future research directions. Following this topic, Yin et al. [3] analyze the work hardening behaviour of GCr15-bearing steel during rolling contact fatigue. They establish a dislocation-based work hardening model by combining the Kocks–Mecking theory, the bearing steel plasticity equation and the Taylor relation [3]. The resulting model can predict hardness changes with any given rolling contact stress state and the number of cycles and was validated by experimental results.

The next two contributions study fatigue crack growth rates under environmental effects. Álvarez et al. [4] investigate the effect of internal hydrogen on the fatigue crack growth rate of the coarse grain region of a 2.25Cr1Mo steel welded joint. The fatigue crack growth rate was measured in the compact tensile specimens of base materials and coarse-grain heat-affected zones, with different stress ratios and frequencies. Hydrogen embrittlement proved to be more significant for the lower frequency and higher load ratio analyzed in this contribution, producing a modification of failure mechanisms. Arrieta et al. [5] propose a procedure for measuring the fatigue crack growth rate using a direct current potential drop in simulated pressurized water reactor conditions. This technique is applied on austenitic stainless steel solid bar specimens, without any notches or pre-cracks. The results of the average crack growth rate were compared with the values obtained by striation spacing measurements in SEM fractography and estimations from NUREG/CR-6909, providing reasonable accuracy in both cases.

The final article, by Toribio and Lorenzo [6], analyzes the effects of the skin pass technique on the residual stress and the plastic strain fields generated in cold drawn pearlitic steel wires. The authors focus on the improvement of the conditions to be used in the manufacturing process in order to obtain more reliable structural components in terms of hydrogen embrittlement, providing a number of useful recommendations.

3. Conclusions and Outlook

The contributions of this Special Issue provide different advances in fatigue and structural integrity research. Their application affects a wide number of engineering sectors, such as mechanical, civil, automotive, material fabrication and energy, among others. In these fields, engineering applications still require further development and enhancement in the coming years, due to the numerous remaining open issues. As guest editors, we hope that this Special Issue provides some insights into the field and that scientific and engineering communities find the works relevant and interesting.

Last but not least, we would like to thank all authors for their contributions and all reviewers for their outstanding efforts to improve the scientific quality of the documents. We would also like to give special thanks to all staff at the Metals Editorial Office and especially Betty Jin, who managed and simplified the publication process.