**2. Fatigue of welded sections**

When we talk about the welded structure, the analysis of fatigue properties becomes even more critical. Whether solid-state or fusion [8–15], the welding processes can be considered the most widely used joining method to fabricate metallic structures, components, bridges, cranes, low and heavy-duty machines, etc. Several of these are designed and developed to have sustainability for a more extended period under fatigue loading. Typically in a welded component, the fatigue failure occurs either across root or toe of weld. Hence this becomes critical to align the design consideration to avoid premature failure under fatigue loading without incurring any noticeable cost. An initial assessment of the actual fatigue life may facilitate designers for obtaining objectives mentioned above.

Current industries put their massive effort into remote design, analysis, and validation of the structural/welded components, followed by their finite element analysis (FEM) to cater the future requirements [16]. This eliminates the time and cost involved in developing and test expensive pre-fabricated prototypes. The use of FEM also facilitates reducing cycle time and expediting inclusion to production sequence. This does also facilitates quick product development, faster launching into the external market. However, remote design and development of components face many challenges, some of which will be discussed in the forthcoming paragraphs.

As we know, that under fatigue loading, the structure or weld section undergoes permanent failure. The estimation of fatigue can be comprised of initiation of cracks and their propagation until final failure. The fatigue process is often found to originate across the stress concentration region, for example, across the weld toe. Nucleation cum spread of fatigue crack is measured based on the magnitude of stress across the favorable crack planes. Society of Automotive Engineers (SAE) has provided an easy information flow chart to determine and analyze stress and fatigue (**Figure 1**). Herein the structure geometry, material properties, and load profile are the significant variables to identify the fatigue life of a component. Usually, the weld joints are the weakest section in a structure, and fatigue failure is most likely to occur across these regions. Therefore to avoid the material failure under fatigue action, the designer needs to establish a relation to calculate the fatigue of structure and weld sections accurately.

In a review paper, Fricke [18] described various techniques to predict the fatigue life for seam welds. Niemi [19] and Fricke [20] covered various recommendations in context to analyze the fatigue behavior of weld joints. The importance

**Figure 1.** *Stages of stress and fatigue analysis [17].*
