PSI - Issue 75

Per-Olof Danielsson et al. / Procedia Structural Integrity 75 (2025) 572–580 Per-Olof Danielsson et al. / Structural Integrity Procedia (2025)

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The variables used in this paper are defined in Table 1.

Table 1: Relevant variables and their symbols.

Nomenclature a

crack length

a i a f

initial crack length final crack length

stress intensity factor in mode I as a function of a

K I (a)

stress



material constant governing the rate of crack growth

C m

exponent that defines the sensitivity of crack growth to the stress intensity factor range

2. Background 2.1. Traditional Approach

Historically, fatigue design and production of welded structure relied on conservative engineering practices. Nominal stress methods and the effective notch stress method have been dominant but have significant limitations, particularly in complex structural applications. Nominal stress methods struggle with complicated geometries and fail to account for critical features like weld roots. The effective notch stress method, while more accurate for complex welded structures, requires extensive computational resources and lacks accuracy under certain common stress conditions. Fracture mechanics methods, though precise in crack growth predictions, are too complex for routine industrial use. Traditional load estimation methods predominantly used physical strain gauge measurements. This process, see Fig 2., proved time-consuming, resource-intensive, and often introduced inaccuracies leading to significant data scatter. Furthermore, the calibration of strain gauge setups was challenging to perform precisely, affecting the reliability of the gathered data. Additionally, physical measurements offered limited synchronization among various load inputs, often failing to provide explicit force data at specific load introduction points. Consequently, these conservative methodologies frequently resulted in excessive structural weight and increased production costs, hindering the efficient development and adoption of advanced physics-based fatigue analyses. In design processes, the traditional approach with the Effective Notch Stress (ENS) method required the creation of separate CAD models specifically tailored for finite element (FE) analysis, including detailed notches at weld toes and roots. This represented additional workload for designers, whose efficiency and quality of outcomes were highly dependent on their individual skill levels, thus significantly extending the time required for design iterations. In manufacturing, designs frequently suggested improved weld quality to mitigate high-stress locations; however, such enhancements often fell outside standard production flows. This mismatch created operational difficulties, making it challenging to consistently achieve efficient and optimized welded structures. 2.2. Enablers and Technological Advancements Over recent decades, the integration of digital tools and virtual simulations has profoundly improved engineering practices. Advances in computational power have accelerated finite element modeling (FEM), virtual simulations, and fatigue analysis capabilities. Virtual modeling of vehicle operations on digitized test tracks has largely replaced extensive physical testing, resulting in improved consistency and accuracy in load estimations. Additional enabling technologies include increased computational processing capabilities, expanded data storage, and the broader application of digital tools, allowing more extensive and detailed component and scenario analyses.