Reporter: Yong Wang Supervisor: Professor Xu Chen

1. Study on the Uniaxial Cyclic Behaviors of Primary Auxiliary Piping Materials in Nuclear Power Plant at room and Elevated Temperatures Reporter: Yong Wang Supervisor: Professor Xu Chen

2. contents • significance of choosing this topic • Literature Review • project planning

3. significance of choosing this topic • Engineering components are often subjected to cyclic load and the cyclic plastic deformation of engineering materials thus becomes inevitable. Under asymmetrical cyclic stressing, cyclic accumulation of plastic deformation, denoted as ratcheting, takes place. ratcheting is very important and should be addressed in the safety assessment and fatigue life estimation of the materials and structure components. Design criteria for nuclear power plants, such as ASME Code Section III, KTA and RCC-MR, all require ratcheting analysis.

4. References • [1] J.L. Chaboche, D. Nouailhas, Constitutive modeling of ratcheting effects. Part I. Experimental facts and properties of classical models, ASME J. Eng. Mater. Technol. 111 (4)(1989) 384–392. • [2] M.D. Ruggles, E. Krempl, The interaction of cyclic hardening and ratcheting for AISI type 304 stainless steel at room temperature. I. Experiments, J.Mech. Phys. Solids 38 (4) (1990) 575–585. • [3] P. Delobelle, P. Robinet, L. Bocher, Experimental study and phenomenological modelization of ratcheting under uniaxial and biaxial loading on an austenitic stainless steel,Int. J. Plast. 11 (4) (1995) 295–330. • [4] D.L. McDowell, Stress state dependence of cyclic ratcheting behavior of two rail steels, Int. J. Plast. 11 (4) (1995)397–421. • [5] M. Kobayashi, N. Ohno, T. Igari, Ratcheting characteristics of 316FR steel at high temperature, Int. J. Plast. 14(4–5) (1998) 355–390. • [6] M. Mizuno, Y. Mima, M. Abdel-Karim, N. Ohno,Uniaxial ratcheting of 316FR steel at room temperature.I. Experiments, ASME J. Eng. Mater. Technol. 122 (1)(2000) 29–34.

5. References • [7] G.Z. Kang, Q. Gao, X.J. Yang, Y.F. Sun, An experimental study on uniaxial and multiaxial strain cyclic characteristics and ratcheting of 316L stainless steel, J. Mater. Sci.Technol. 17 (2) (2001) 219–223. • [8] G.Z. Kang, Q. Gao, L.X. Cai, X.J. Yang, Y.F. Sun,Experimental study on the non-proportional cyclic plasticity of U71Mn rail steel at room temperature, J. Mater.Sci. Technol. 18 (1) (2002) 13–16. • [9] G.Z. Kang, Q. Gao, L.X. Cai, Y.F. Sun, Experimental study on uniaxial and nonproportionally multiaxial ratcheting of SS304 stainless at room and high temperatures,Nucl. Eng. Des. 216 (2002) 13–26. • [10] G.Z. Kang, Q. Gao, X.J. Yang, Experimental study on the cyclic deformation and plastic flow of U71Mn rail steel,Int. J. Mech. Sci. 44 (8) (2002) 1645–1661. • [11] Yu, D., et al. Visco-plastic constitutive modeling on Ohno–Wang kinematic hardening rule for uniaxial ratcheting behavior of Z2CND18.12N steel. Int. J. Plasticity (2011), doi:10.1016/j.ijplas.2011.06.001. • [12] Zhu J et al. Bending ratcheting tests of Z2CND18.12 stainless steel. Int J Fatigue (2011), doi:10.1016/j.ijfatigue.2011.04.008.

6. Material categories • cyclic hardening materials:SS304,316FR,316L, Z2CND18.12 et al. • cyclically stable materials(within a limited cyclic number):U71Mn rail steel ,ordinary carbon steel et al. • cyclic softening materials: 25CDV4.11 steel et al.

7. summary • Cyclic hardening/softening behavior, stress magnitude ,mean stress, loading rate, loading history , loading pattern (proportional or non-proportional) ,temperature are some of the variables that would influence the material ratcheting phenomena.

8. Existing problems Primary auxiliary pipeline in nuclear power Plant endures thermal cyclic loading induced by power on and off of reactors. It is necessary to study cyclic behaviors influenced by thermal cyclic aging. It has been found that variation of ambient temperature is common to structure components of nuclear system, and the effect of ambient temperature on the ratcheting is remarkable. Therefore, Cyclic tests should be done to investigate the strain stress response of Z2CND18.12 at high temperature(350℃). thermal shock may occur due to temperature control failure. So, in this case, cyclic tests should be included for thermal shock specimens. Pre-stress/pre-strain cyclic tests are needed for pipeline may endure high loading shock induced by seismic loading.

9. experiment apparatus • high temperature fatigue testing machine

10. Geometry of the specimen Thickness:4.5mm Specimens were fabricated from primary auxiliary heat transport pipes in nuclear power Plant with 76 mm outer diameter and 4.5 mm wall thickness

11. Monotonic tension It has been found that Z2CND18.12 austenitic stainless steel is rate-dependent material(Yu, D., et al.,2011) . So monotonic tensile were performed at various strain rate to understand this feature.

12. Thermal cyclic aging tests Firstly, Specimens were preheated for 30 and 60 cycles, respectively Then, ratcheting cycling under stress control with stress rate of 100MPa/s

13. Thermal shock tests • Specimens were preheated to 500℃ within 1 hour and held for 10 hours then cooled down to room temperature in furnace • Then, cycling tests were conducted at room temperature under strain control and stress control, respectively

14. Pre-strain cycling tests • Specimens were first stretched to 5% and unloaded under strain control with strain rate of 1×10-3 / s • Then symmetric strain cycling with strain amplitude of 1% Asymmetric strain cycling tests with strain amplitude of 1% and mean strain of 5% for comparison

15. Strain cycling tests

16. Pre-stress cycling tests • Specimens were first stretched to maximum stress 350MPa and unloaded under stress control with stress rate of 100MPa/s • Then asymmetric stress cycling with stress amplitude of 150MPa and mean stress of 150MPa Asymmetric stress cycling tests with stress amplitude of 150MPa and mean stress of 150MPa for comparison

17. stress cycling tests

18. Thank you