13th International Conference on Fracture June 16–21, 2013, Beijing, China -10- 4. Discussion and concluding remarks A three bar structure has been designed to simulate the behaviour of a component subjected to combined applied and residual stresses. The properties of the three bar system are determined depending when the long range residual stress (state 1) is induced and following application of an external load (state 2). Closed form solutions of the elastic follow-up factor for states 1 and 2 are given and we find that the expression for elastic follow-up factor in state 2 changes when corresponding residual stress relaxes to zero. Calculations performed to predict creep crack initiation in the presence of long range residual stress in Type 316H austenitic stainless steel provide results that yield significant insight to the behaviour of the system. Sensitivity studies have been included to determine the influence of changes in the material creep properties and the effects of elastic follow-up factor on stress relaxation. We find that the predictions of crack initiation are sensitive to both the creep constants and elastic follow-up factors respectively. However, the initiation times for different constants and different Z tend to converge to similar values for low initial reference stresses. In state 2, the effect of residual stress on crack initiation is found to depend on the value of total stress (residual stress plus stress created by applied load) and the ratio of the residual stress to total stress. The elastic follow-up factor decreases significantly in state 2 when all of the residual stress has relaxed to zero. Acknowledgements The authors gratefully acknowledge the support provided by EDF Energy for this work. References 1. P. J. Bouchard, P.J.W., S. A. McDonald, R. K. Heenam, Quantification of creep cavitation damage around a crack in a stainless steel pressure vessel. Acta Materialia, 2004. 52. 2. Mahmoudi, A.H., Aird, C., Truman, C.E., Mirzaee-Sisan, A., Smith, D.J., , Generating well defined residual stresses in laboratory specimens, in paper PVP2006-ICPVT11-93620, Proceedings of PVP2006: ASME Pressure Vessels and Piping Division Conference2006: July 23-17, 2006, Vancouver, Canada. 3. Kasahara, N., Strain concentrations at structural discontinuities and its prediction on characteristics of compliance change in structures. JSME Int. J.,, 2001. 44: p. 354-361. 4. A. M. Shirahatti, Y.W., C. E. Truman, D. J. Smith, A new method of introducing long range residual stress to study creep crack initiaion, in 13th International Conference on Fracture2013: Beijing, China. 5. R5-Assessment procedure for the high temperature response of structures, Revision3, 2003: British Energy Generation Limited, Gloucester, UK. 6. M. Turski, P.J.B., A. Steuwer, P. J. Withers, Residual stress driven creep cracking in AISI Type 316 stainless steel. Acta Materialia, 2008. 56: p. 3598-3612.
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