Failure Mechanisms in Alloys

based on the relevant “Investigation Method / Approach” followed in the studies of this Special Issue.

. The failure analysis "knowledge triangle", presenting the interaction areas and the central role of the understanding of a material or component's role and properties.

Contributions
The Special Issue "Failure Mechanisms in Alloys" contains in total twenty-seven (27) research articles , with two review papers among them (see [9] and [24]). The contents of this collection cover a wide spectrum of the cross-disciplinary fields of the entire domain of failure analysis, providing valuable contributions in diverse and challenging topics exhibiting interests in the investigation of failure mechanism, industrial processes, and approach methods (Figures 2-4). Moreover, different groups of materials are involved in the presented studies (Table 1).
Almost the complete range of the general types of failure mechanisms has been addressed in the published works gathered in this Special Issue. Instant overload as well as progressive failure modes are included (Figure 2a). More specifically, the broad category of static overload includes more generic subjects also from the field of manufacturing-related topics, where the effect of deformation and fracture was studied as an important and undetached ingredient of the fabrication process per se (e.g., hot and cold working, machining). Therefore, the mostly "intense area" (Overload/Static) comprises studies concerning general deformation and fracture phenomena, as the result of instant loading/testing conditions [4,9,10,14,15,19] and studies related to manufacturing and production processes [6,7,12,13,16,20,22,25,26]. Testing and modeling procedures addressing the evolution of deformation and fracture during forming [7,13,26], the impact toughness, [4] and certain production process characteristics [25] are also included. Nevertheless, shear fracture processes that emerged in machining and chip formation are also part of this broader group of studies, relevant to manufacturing topics (see [12,16,20]).

Contributions
The Special Issue "Failure Mechanisms in Alloys" contains in total twenty-seven (27) research articles , with two review papers among them (see [9] and [24]). The contents of this collection cover a wide spectrum of the cross-disciplinary fields of the entire domain of failure analysis, providing valuable contributions in diverse and challenging topics exhibiting interests in the investigation of failure mechanism, industrial processes, and approach methods (Figures 2-4). Moreover, different groups of materials are involved in the presented studies (Table 1).
Almost the complete range of the general types of failure mechanisms has been addressed in the published works gathered in this Special Issue. Instant overload as well as progressive failure modes are included ( Figure 2a). More specifically, the broad category of static overload includes more generic subjects also from the field of manufacturing-related topics, where the effect of deformation and fracture was studied as an important and undetached ingredient of the fabrication process per se (e.g., hot and cold working, machining). Therefore, the mostly "intense area" (Overload/Static) comprises studies concerning general deformation and fracture phenomena, as the result of instant loading/testing conditions [4,9,10,14,15,19] and studies related to manufacturing and production processes [6,7,12,13,16,20,22,25,26]. Testing and modeling procedures addressing the evolution of deformation and fracture during forming [7,13,26], the impact toughness, [4] and certain production process characteristics [25] are also included. Nevertheless, shear fracture processes that emerged in machining and chip formation are also part of this broader group of studies, relevant to manufacturing topics (see [12,16,20]).   Creep and Creep Fatigue failure modes [2,9,17,23]; b.
The relevant number of studies' distribution graph is presented in Figure 2b. It can be seen from Figure 2b that manufacturing-related topics occupy a significant percentage of the content, reflecting the importance of failure assessment and the emergence of failure and damage prognosis and prevention, as the basic component of the knowledge and learning processes required for quality improvement in industry.
The relevant number of studies' distribution graph is presented in Figure 2b. It can be seen from Figure 2b that manufacturing-related topics occupy a significant percentage of the content, reflecting the importance of failure assessment and the emergence of failure and damage prognosis and prevention, as the basic component of the knowledge and learning processes required for quality improvement in industry.
Considering the "Process/Industry" as a classification criterion, the published studies are relevant with certain industries or processes involved as far as the observed failure mechanism is concerned ( Figure 3). More specifically, the main industrial processes involved are presented as follows: (i) Casting and Metal Forming [6,7,11,13,15,19,[24][25][26] (ii) Machining [12,16,20] (iii) Chemical/Petrochemical [3,17,21,23] (iv) Heat Treatment [22] (v) General Plant Machinery [1,9,18,24]  The metal component manufacturing industry (casting, metal forming, and machining) seems to be highly involved, as one of the primary industrial component production sectors, in highlighting the efforts in understanding material behavior and taking actions for failure prediction and prevention.
Based on the "Investigation Method/Approach", several broad categories can be distinguished ( Figure 4) [3,[6][7][8][12][13][14][15][16][18][19][20]22,25,26] As can be readily observed, the experimental and empirical approach is the dominant methodology of failure investigation. In addition, the emergence of numerical simulation, using finite element modeling (FEM), tends to be very popular in the prediction of material behavior and potential failure prevention. The contribution of quality and organization systems is very promising in the case of complex processes, where teamwork in process planning, risk assessment, resource The metal component manufacturing industry (casting, metal forming, and machining) seems to be highly involved, as one of the primary industrial component production sectors, in highlighting the efforts in understanding material behavior and taking actions for failure prediction and prevention.
Based on the "Investigation Method/Approach", several broad categories can be distinguished ( Figure 4) [3,[6][7][8][12][13][14][15][16][18][19][20]22,25,26] As can be readily observed, the experimental and empirical approach is the dominant methodology of failure investigation. In addition, the emergence of numerical simulation, using finite element modeling (FEM), tends to be very popular in the prediction of material behavior and potential failure prevention. The contribution of quality and organization systems is very promising in the case of complex processes, where teamwork in process planning, risk assessment, resource allocation, and implementation of improvement actions is a key concept in modern quality assurance and management.
Metals 2020, 10, x FOR PEER REVIEW 5 of 7 allocation, and implementation of improvement actions is a key concept in modern quality assurance and management. A broad range of materials was covered in the present studies (see Table 1). Ferrous metals (structural steels, stainless steels, and special resistance steels) are more frequently investigated, indicating the importance of this material type in engineering constructions and in severe process environments. Table 1. Representative types of engineering material types of investigation.

Conclusions
The present collection of studies reflects the profound interest in the specific field of research, covering a wide range of failure mechanisms, processes, and investigation methodologies. The majority of the studies followed a phenomenological and experimental approach, while it seems that there was a general contribution tendency toward numerical simulation, to further enrich the value of the research results and broaden the application perspectives, especially in the case of larger-scale metal-forming and manufacturing processes. Ferrous alloys (structural, special purpose or resistance, stainless steels, cast irons) constitute the majority of the studied materials, since they are considered one of the principal sources of construction components and are used in various industrial sectors.
On a final note, it is hoped and strongly believed that the accumulation of additional knowledge in the field of failure mechanisms and the adoption of the principles, philosophy, and deep A broad range of materials was covered in the present studies (see Table 1). Ferrous metals (structural steels, stainless steels, and special resistance steels) are more frequently investigated, indicating the importance of this material type in engineering constructions and in severe process environments. Table 1. Representative types of engineering material types of investigation.

Conclusions
The present collection of studies reflects the profound interest in the specific field of research, covering a wide range of failure mechanisms, processes, and investigation methodologies. The majority of the studies followed a phenomenological and experimental approach, while it seems that there was a general contribution tendency toward numerical simulation, to further enrich the value of the research results and broaden the application perspectives, especially in the case of larger-scale metal-forming and manufacturing processes. Ferrous alloys (structural, special purpose or resistance, stainless steels, cast irons) constitute the majority of the studied materials, since they are considered one of the principal sources of construction components and are used in various industrial sectors.
On a final note, it is hoped and strongly believed that the accumulation of additional knowledge in the field of failure mechanisms and the adoption of the principles, philosophy, and deep understanding of the failure analysis process approach will strongly promote the learning concept as a continuously evolving process, leading to personal and social progress and prosperity.
Funding: This research received no external funding.