PSI - Issue 57

Kaushik Iyer et al. / Procedia Structural Integrity 57 (2024) 469–477 Kaushik Iyer, et.al. / Structural Integrity Procedia 00 (2019) 000 – 000

472

4

Leg Length Penetration

4 mm 100%

6 mm 100%

3. Methodology 3.1. Fatigue Design Calculations

The operational costs of a welded structure can be assumed to be a function of the fatigue design of the structure. Due to the inclusion of repair and maintenance costs, it is essential to accurately calculate the fatigue life of a structure under load. The fatigue stress and life of a weld can be calculated using several methods including deterministic methods such as the nominal stress method and the structural hot spot stress method, and probabilistic methods. However, these fatigue calculation methodologies vary both in accuracy and complexity. In this study, the effective notch stress method (NS) is used to estimate the fatigue lives of the as-welded and the HFMI treated samples. The fatigue life was estimated according to, = ∗ ( ) (1) Where FAT is the Fatigue strength class of the weld according the IIW recommendations (Marquis and Barsoum 2016), m is the slope of the S-N curve and is the equivalent notch stress. The equivalent notch stress was calculated numerically using a FEM model in the ANSYS Mechanical solver module. The life of the welded samples was evaluated for a nominal load of 100 MPa and 150 MPa respectively. Additionally, the element sizes of the FEM model were determined according to the IIW recommendations for the effective notch stress method. Furthermore, the equivalent stress of the sample was evaluated at the weld toe for a notch radius of 1 mm. The respective FAT classes and S-N curve slopes for the as-welded and the HFMI treated samples according to the IIW recommendations are given in Table 2. 3.2. Life-cycle costing Life-cycle costing is an approach that assesses the total cost of an asset or a product over its life-cycle including initial capital investment costs, maintenance costs, operating costs, and the residual value at the end-of-life (EOL) stage (Sesana and Salvalai 2013). In this study, the product is assumed to undergo a life-cycle as shown in Figure 3.While the costs incurred in the phases of resource extraction, use-phase and End-of-life can be estimated using data obtained from literature, industry values and other databases, the manufacturing costs incurred were estimated using an Activity based Costing (ABC) methodology. ABC as a costing methodology can be defined as an approach which assigns activities as the major cost drivers (Bhimani 2001). The life-cycle cost of the part can be considered as the cumulative sum of the costs incurred during the individual life-cycle phases as given by, = + + + (2) Table 2: FAT classes for S355 steel FAT Class S-N curve slope AW sample 225 320 3 5 HFMI treated sample