13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- 5. Summary and Conclusions Finite element analysis was performed for a cruciform specimen containing weld joint and being subjected to biaxial cyclic loads. First, stress distribution and out-of-plane deformation are determined to assess the effect of secondary bending on fracture mechanics parameters. Second, influence of biaxial stress on crack growth behaviour is modelled, and fatigue crack growth life is predicted using calculated stress intensity factors and weld metal crack growth rates measured from M(T) specimens made of the same material and same welding process. Main conclusions are: 1. Mode-I stress intensity factor (SIF) decreases as the biaxial load ratio k increases. Comparing to the uniaxial load case (k = 0), reduction in SIF is 12% (k = 1) and 24% (k = 2). 2. For k ≤ 1, no crack path deviation is predicted by the analysis; models show very small deviation when a crack is longer than half of the panel width. For k = 2small deviation is predicted. The model solution is in agreement with the fracture mechanics theory based on the mode II SIF and elastic T stress. 3. Test observed crack turning is larger than model prediction. This could be due to a few complex factors that are not considered in the present FE model, such as weld metal microstructure, anisotropic material properties, and residual stress in the weld longitudinal direction. Acknowledgement The authors are grateful for the financial support from the European Union through its Sixth Framework Programme under the “cost effective integral metallic structures” project. They also thank Drs. Richter-Trummer and Dos Santos at Helmholtz-Zentrum Geesthacht Germany for providing test data. The modelling work was conducted at Cranfield University. References 1. Bussu G, Irving PE. The role of residual stress and heat affected zone properties on fatigue crack propagation in friction stir welded 2024-T351 aluminium joints, Int J Fatigue, 25(2003): 77-88. 2. Pouget G, Reynolds AP. Residual stress and microstructure effects on fatigue crack growth in AA2025 friction stir welds, Int J Fatigue, 30(2008): 463-472. 3. Glinka G. Effect of residual stresses on fatigue crack growth in steel weldments under constant and variable amplitude load. In: Fract. Mech., ASTM STP 677, American Society for Testing and Materials, 1979, pp. 198-214. 4. Beghini M, Bertini L, Vitale E. Fatigue crack growth in residual stress fields: experimental results and modelling. Fatigue Fract Engng Mater Struct 1994; 17: 1433-1444. 5. Ghidini T, Dalle Donne C. Fatigue crack propagation assessment based on residual stresses obtained through cut-compliance technique, Fatigue & Fracture of Eng Mater & Struct, 30(2006): 214-222. 6. Fratini L, Pasta S, Reynolds AP, Fatigue crack growth in 2024-T351 friction stir welded joints: longitudinal residual stress and microstructural effects. Int J Fatigue 2009; 31: 495-500. 7. Servetti G, Zhang X. Predicting fatigue crack growth rate in a welded butt joint: the role of effective R ratio in accounting for residual stress effect. Eng Fract Mech 76 (2009) 1589-1602. 8. Cotterell B. International J of Fracture Mechanics, 2 (1966): 526-533.
RkJQdWJsaXNoZXIy MjM0NDE=