PSI - Issue 75

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

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through one of the following methods: • Estimation based on the fatigue limit strength, ∆ ℎ , and the threshold stress intensity range, ∆ ℎ , determined at the same stress ratio: ∗ = 1.633 2 2 ∙ ( ∆ ℎ ∆ ℎ ) 2 (14) • Estimation based on the strain-life (EN) curve and limited fatigue crack growth data. The advantage of this method is that it could avoid the need for further expensive testing, as it requires test data that is often already available. • Estimation based on experimental fatigue crack growth data at various stress ratios. This is the most robust approach. The effective crack-tip radius, ∗ , is defined as the value that maximises the Spearman rank correlation amongst test data at various stress ratio.

Fig. 6. Estimation of ∗ through collapse of fatigue crack growth test data at different stress ratio.

3. Implementation of the ‘Total - Life’ Method in the CAE environment The ‘T otal-Life ’ method ha s been implemented in the nCode ‘WholeLife’ analysis engine. ‘WholeLife’ uses as input the stresses resulting from a finite element (FE) model of the structure of interest and performs crack growth calculations at critical locations. It supports both shell and solid elements, and it has got the advantage of allowing the use of coarse FE meshes. Furthermore, it avoids the need to physically model the crack in the FE analysis, allowing for faster and more economical FE analysis, by calculating the stress intensity at the crack tip as a function of the stress distribution along the crack path (assuming an uncracked section) through the ‘Universal Weight Function’ (UWF) approach described by Glinka and Shen (1991). The nC ode ‘WholeLife’ analysis engine includes an extensive catalogue of UWF solutions for a wide range of crack/component geometries. Material data (e.g. stress strain curve, crack growth curve), through-thickness notch stress concentration profiles and, optionally, the residual stress profile along the crack path are additional inputs required by the ‘WholeLife’ analysis engine. An example of ‘WholeLife’ analysis flow is shown in Fig. 7. It is worth noting that to reduce the computation time, the ‘WholeLife’