V.O. STRYZHALO AND L.S. NOVOGRUDSKIY

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 USSRaimed at creating a fusion reactor with a superconducting electromagnetic system for plasma confinement whose construction is planned to start in 2007.

2. s s d y , , , , 0 . 2 u Grade % % MPa MPa 304 LN 1863 724 48.0 53.0 316 LN 1450 990 - - CSUS-JN 1820 1430 40.0 - 1 CSUS-JN 1640 1240 36.0 - 2 03Kh20N 16 A G6 1700 1440 30.0 42.0 REQUIREMENTS FOR STRUCTURAL MATERIALS FOR ITER SUPERCONDUCTING ELECTROMAGNETIC SYSTEMS (SEMS) Н=13 Tesla; J = 22 kA/m2; = 740 MPa; Т=4.2 K T = 4.2 K AISI 304 AISI 316 Inconel 750 MFTF (USA) 400 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 AISI 310 JAERI (Japan) 300 Mechanical characteristics of steels showing promise as ITER SEMS materials at 4.2 K 200 03Kh20N16АG6 (Ukraine) Ti-6Al-4V 100 A 266 Ti-5Al-2.5Sn 0 MPa 700 1400 2100

3. P 1600 N DR b ECP a 0.74 mm LOAD-ELONGATION CURVES FOR 12KH18N10T STEEL SUBJECTED TO ELECTRIC CURRENT PULSES (ECP) AND A TEMPERATURE OF 4.2 K

4. - 2 1 = t = J 2 50 М А/m ; 10 s 1 / 2 t é ù 0 . 2 ò ò cur 2 s = s e - lr 2 E d J ( t ) dE ê ú 0 ë û 0 0 l = D s s / 0 . 2 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 Criterion I cur s = s -12Kh18N10T equivalent Danger (0) -03Kh13AG19 -03Kh20N16AG6 -PT3V (1) 1.0 , coefficient of material’s sensitivity to ECP, – J – current density, r – electrical resistivity, 0.5 t E – pulse duration – Young’s modulus - solid line, - dashed line

5. STRAIN AND STRAIN CONCENTRATION FACTOR KINETICS FOR 03KH20N16AG6 STEEL Strain concentration factor Strain intensity at the notch tip Nominal strain intensity 1.2 4.2 K 0.4 0.8 0.2 0.4 4.2 K 0.5 0.94 1.38 1.82 2.28 σn, MPa σn, MPa 1.38 1.38 1.82 2.28 σn, MPa 0.5 0.94 1.82 2.28 0.5 0.94 open dots – initial state, solid dots - action of ECP Criterion II PC (2, 3) strain hardening exponent

6. J J c, c 2 æ ö K 1 ç ÷ = c r 1 ç ÷ s k è ø 0 , 2 2 cur = r r cr cr 1 3 2 æ ö cur K 1 ç ÷ cur = = с r r ç ÷ cr cur s k è ø 0 1 – AMnS; 2 – АМg6; 3 – АМg5 æ ö e l rcr 1 ç ÷ cur 2 s = ò s e - t £ e £ e = 2 E d I R , 0 ç ÷ 0 1 1 2 V l è ø 0 0 cur cur = s K krcr с 0 æ ö e l 1 ç ÷ cur 2 = ò s e - t К krcr 2 E d I R ç ÷ с 1 2 V è ø 0 -2 cur = = t = s = = Т 4 . 2 К ; I 2800 A; 10 c ; 1186 MPa; ; К 58 MPa m ; 0 Ic cur = K 55 MPa m I с EFFECT OF TEMPERATURE ON THE ALLOY FRACTURE TOUGHNESS ALUMINIUM ALLOYS k 2 , kJ/m 75 - radius of the plastic zone at the crack tip 50 kpl.strain.st.= 6p, kpl.stress.st. @ 2 p; Kcis the stress intensity factor 25 Criterion III defined by the radius of the plastic zone at the crack tip , (4) 0 100 200 T, K STEELS k 2 J J , kJ/m c c where . 1 Knowing the Kc value, we can calculate it for the action of PC as follows: 400 2 3 4 (5) 200 . 5 6 ОN9 7 0 100 200 Т, К 1 - 12Kh18N10Т; 2 – 03Kh20N16АG6Sh; 3 – 07Kh13N4АG20; 03Kh20N16АG6; 5 – 03Kh19АG3N10; 4 – 6 – 03Kh13N9G19АМ2; 7 - ОN9

7. [ ] 1 ( ) ( ) ( ) 2 2 2 s = s - s + s - s + s - s = s equiv 1 2 2 3 3 1 r 2 cur cur s = s s = s ; s = s = s s = ; 0 equiv r equiv r 1 2 r 3 1 / 2 é ù æ ö l 0 . 2 ç ÷ ò cur cur cur 2 s = s £ s = s e - p t 2 Е d R ê ú ç ÷ equiv r 0 2 V è ø ë û 0 cur s 0 cur s r D e UNIFORM BIAXIAL TENSION Von Mises Condition of ultimate stateoccurrence : (6) = 647 MPa Steel 07Kh13N4АG20, Т= 77 К, – ( calculated value) Experiment 261.5 379.0 655.0 750.0 , MPa , % 0 0 0.21 0.36

8. CONCLUSIONS • 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 zoneradius at the crack tip, • - stress intensity at a complex stress state, .