PSI - Issue 75

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

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5. Conclusions A unified fatigue life estimation approach, known as ‘ Total-Life ’ method, was thoroughly described. The ‘ Total Life ’ method takes into account both the initiation and propagation stages, by combining principles from strain-life and fracture mechanics together with a state-of-the-art multiaxial crack-tip plasticity model that accounts for mean stress and overload retardation effects. This method is particularly beneficial in applications where both initiation and propagation stages are significant, such as welded structures, lightweight jointed structures, and lightweight cast components, for which most traditional simulation methods, that focus on either crack initiation or crack propagation stage, can produce inaccurate fatigue life predictions. The ‘TotalLife’ method has been implemented in the nCode ‘WholeLife’ analysis engine. ‘WholeLife’ supports both shell and solid elements and allows faster and more economical FE analysis by avoiding the need for fine FE meshes and to physically model the crack. The other main advantages of ‘WholeLife’ compared to traditional weld fatigue analysis techniques are: • Both the initiation and propagation stages are taken into account. • The effects of residual stresses can be considered. • Usage of generalized universal weight functions to account for the effect of the geometry of components and welded joints. • Sensitivity to initial crack length assumptions is removed. • Multiaxial loading can be analysed. References Bogdanov, S., 2015. Fatigue Life Prediction Based on the Advanced Fatigue Crack Growth Model and the Monte-Carlo Simulation Method. PhD thesis, Waterloo, Ontario, Canada: University of Waterloo. Cordes, T., Norton, E., Brown, H., Munson, K., 2019. Comparison of Total Fatigue Life Predictions of Welded and Machined A36 Steel T-Joints. SAE Technical Paper 2019-01-0527. Creager, M., Paris, P. C., 1967. Elastic field equations for blunt cracks with reference to stress corrosion cracking. International Journal of Fracture Mechanics 3(4), 247 – 252. Elber, W., 1971. The Significance of Fatigue Crack Closure. Damage Tolerance in Aircraft Structures, 230 – 242. Glinka, G., 1985. Calculation of inelastic notch-tip strain-stress histories under cyclic loading. Engineering Fracture Mechanics 22(5), 839 – 854. Glinka, G., Shen, G., 1991. Universal features of weight functions for cracks in mode I. Engineering Fracture Mechanics 40(6), 1135 – 1146. Glinka, G., 2015a. Personal correspondence. Glinka, G., 2015b. Personal correspondence on the effect of at long distances from the crack tip. Landgraf, R. W., Morrow, J., Endo, T., 1969. Determination of the cyclic stress-strain curve. ASTM Journal of Materials 4(1), 176-188. Mikheevskiy, S., 2009. Elastic-plastic fatigue crack growth analysis under variable amplitude loading spectra. PhD thesis, Waterloo, Ontario, Canada: University of Waterloo. Mikheevskiy, S., Glinka, G., 2009. Elastic – plastic fatigue crack growth analysis under variable amplitude loading spectra. International Journal of Fatigue 31(11 – 12), 1828 – 1836. Moftakhar, A., Buczynski, A., Glinka, G., 1995. Calculation of elasto-plastic strains and stresses in notches under multiaxial loading. International Journal of Fracture 70(4), 357 – 373. Neuber, H., 1961. Theory of Stress Concentration for Shear-Strained Prismatical Bodies With Arbitrary Nonlinear Stress-Strain Law. Journal of Applied Mechanics 28(4), 544 – 550. Noroozi, A., Glinka, G., Lambert, S., 2005. A two parameter driving force for fatigue crack growth analysis. International Journal of Fatigue 27(10 – 12), 1277 – 1296. SAE Fatigue Design and Evaluation Committee, 2018. Summary of Fatigue Life Testing and Analysis of the A36 T-Joint Specimens Machined and Welded Completed Todate. SAE FD&E Semi-Annual Meeting. Walker, K., 1970. The Effect of Stress Ratio During Crack Propagation and Fatigue for 2024-T3 and 7075-T6 Aluminum. Effects of Environment and Complex Load History on Fatigue Life, ASTM STP 462.