PSI - Issue 75

Andrew Halfpenny et al. / Procedia Structural Integrity 75 (2025) 234–244 Author name / Structural Integrity Procedia (2025)

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analysis engine performs an initial solid seam weld analysis to identify the most critical locations where to perform the actual ‘WholeLife’ analysis.

Fig. 7. Example of ‘WholeLife’ analysis flow .

It is important to recognise that, in real applications, the stress profile is likely to change over time due to the multiaxial nature of the input loading. This challenge can be addressed following three approaches: • A new stress intensity is calculated at each point in time based on the constantly varying stress profile along the crack path. The is computationally onerous, as the stress intensity must be recalculated at every cycle due to the cycle-by-cycle nature of the crack growth algorithm. • The stress intensity at each point in time is calculated by superposition of the UWF solutions based on the stress profiles along the crack path calculated for each load case. This approach is computationally less expensive but can be inefficient in case of a large number of load cases. • The stress distributions are decomposed into their membrane and bending components for each load case. The stress intensity is then calculated at each point in time by superposition of the UWF solutions. This is the most efficient and robust method, and it is suitable for both shell and solid finite elements. Furthermore, it is particularly suited for use with coarse mesh models, such as automotive body-in-white models, thanks to the definition of a mesh-insensitive linearized stress profile along the crack plane, . To avoid inaccuracies with stress recovery at nodes on the surface, when the FE model is generated using solid elements, a ‘Through - thickness Integration’ technique is adopted to calculate the linearised membrane, , and bending, , stress components: = 1 ∫ 0 ; = 6 2 ∫ ( 2 − ) 0 (15) where is the through-thickness ( ) stress profile along the crack plane. However, by decomposing the stress profile simply into membrane and bending stress components, it is not possible to describe complex variations in the through-thickness stress profiles. Furthermore, residual stresses, generated for example by manufacturing processes, influence both crack initiation and propagation. To address these issues, the nCode ‘ WholeLife ’ software package also allows to apply through-thickness notch stress concentration profiles as well as residual stress profiles along the crack path: = + + (16)