1. ULTIMATE STATE CRITERIA OF STRUCTURAL ALLOYS FOR SUPERCONDUCTING ELECTROMAGNETIC SYSTEM OF A FUSION REACTOR V.O. STRYZHALO AND L.S. NOVOGRUDSKIY G.S. Pisarenko Institute for Problems of Strength, National Ac. Sci. of Ukraine Kiev, Ukraine Ultimate state criteria of metallic materials exposed to pulses of electric current and cryogenic temperatures are considered and the basic methods for determining their parameters at linear, nonuniform, and complex stress state, as well as in the presence of a crack, are set out. The studies were performed within the framework of the joint international project ITER, which is a joint international research and development project created by the European Union, the People´s Republic of China, India, the Republic of Korea, USA, Japan, and the former USSR aimed at creating a fusion reactor with a superconducting electromagnetic system for plasma confinement whose construction is planned to start in 2007.

2. REQUIREMENTS FOR STRUCTURAL MATERIALS FOR ITER SUPERCONDUCTING ELECTROMAGNETIC SYSTEMS (SEMS) Mechanical characteristics of steels showing promise as ITER SEMS materials at 4.2 K MPa 03Kh20N16АG6 (Ukraine) JAERI (Japan) Ti-6Al-4V T = 4.2 K 400 300 100 200 0 70014002100 AISI 304 AISI 316 AISI 310 A 266 Ti-5Al-2.5Sn Inconel 750 MFTF (USA) Н=13 Tesla; J = 22 kA/m 2 ; = 740 MPa; Т=4.2 K 1- vacuum volume, 2- axial current, 3 – plasma, 4 – toroidal field, 5 – toroidal field coil, 6 – injection point of neutral particle beams, 7 – poloidal field, 8 – field coil, 9 – primary coil of ohmic heating, 10 – resultant field

3. LOAD-ELONGATION CURVES FOR 12KH18N10T STEEL SUBJECTED TO ELECTRIC CURRENT PULSES (ECP) AND A TEMPERATURE OF 4.2 K

4. s 10 ;А/m М 502 12   J Criterion I cur Danger (0)equivalent  2/1 2.0 00 2cur 0 )(2         dEtJdE  , 2.0 /  – coefficient of material’s sensitivity to ECP, J – current density,  – electrical resistivity,  – pulse duration E – Young’s modulus EFFECT OF COOLING DOWN TO 4.2 K ON THE STRESS CORRESPONDING TO THE ONSET OF THE PLASTIC YIELDING IN STEELS AND TITANIUM ALLOYS EXPOSED TO EPC, MPa 1.0 0.5 -12Kh18N10T -03Kh13AG19 -03Kh20N16AG6 -PT3V - solid line, - dashed line (1)

5. STRAIN AND STRAIN CONCENTRATION FACTOR KINETICS FOR 03KH20N16AG6 STEEL Strain intensity at the notch tipNominal strain intensity Strain concentration factor 1.2 0.8 0.4 0.50.941.381.822.28 σ n, MPa 0.5 0.94 1.38 0.2 1.822.28 σ n, MPa 0.50.94 1.38 1.822.28 σ n, MPa 4.2 K 0.4 4.2 K open dots – initial state, solid dots - action of ECP Criterion II PC strain hardening exponent (2, 3)

6. 0 100 200 Т, К 200 400 2 3 4 5 6 7 2 kJ/m, J J k c c 1 EFFECT OF TEMPERATURE ON THE ALLOY FRACTURE TOUGHNESS ALUMINIUM ALLOYS STEELS 100 200 T, K 0 25 50 75 2 kJ/m, k J J c c, 1– AMnS; 2– АМg6; 3– АМg5 1 2 3 1 1- 12Kh18N10Т; 2– 03Kh20N16АG6Sh; 3 – 07Kh13N4АG20; 4– 03Kh20N16АG6; 5 – 03Kh19АG3N10; 6– 03Kh13N9G19АМ2; 7 - ОN9 2 2,0 1           c K k r - radius of the plastic zone at the crack tip k pl.strain.st.  k pl.stress.st.  ; K c is the stress intensity factor cur cr rr  Criterion III defined by the radius of the plastic zone at the crack tip 2 cur 0 с cr 1           K k rr, where 0 1 0 1 2cur 0 0, 2 2 1 l r cr RI V dE              . Knowing the K c value, we can calculate it for the action of PC as follows: cur 0 с kr cr K            1 0 1 2cur с 2 2    RI V dEkr cr К. ОN9ОN9 ;mMPa 58;MPa; 1186;10 A; 2800;К 2.4 cur 0 -2  Ic КcIТ  m MPa 55 cur с  I K (4) (5)

7. Condition of ultimate state occurrence : 2/1 2.0 0 2cur 0 equiv 2 2                   R V dЕ r Steel 07Kh13N4АG20, Т= 77 К, cur 0  = 647 MPa – (calculated value) UNIFORM BIAXIAL TENSION Von Mises   r  2 1 2 13 2 32 2 21equiv  0 ; 321  r cur equiv ; rr  cur r , MPa 261.5 379.0 655.0 750.0 , % 0 0 0.21 0.36 Experiment (6)

8. We propose to characterize the occurrence of ultimate state in metals and alloys subjected to the action of electric current pulses and cryogenic temperatures with the following parameters: - the stress corresponding to the onset of the plastic yielding initiated by an electric current pulse, - strain intensity at the notch root, - critical value of the plastic zone radius at the crack tip, - stress intensity at a complex stress state, CONCLUSIONS.