Fasteners / Joint Design

1. Fasteners / Joint Design Michael Kalish NSTX TF FLAG JOINT REVIEW 8/7/03

2. Outline Assembly Overview Discussion of Preload Review of Design with respect to Cyclic and Static Loading for: Flag Inserts Flag Studs Shear Key Threads Shear Key Bolts Acceptance Criteria

3. Flag Hardware Exploded View

4. Stud Preload • Maintaining the preload on the stud is critical for maintaining contact pressure and contact resistance • Using a long narrow stud results in a much higher stud elasticity relative to the flag • Stud elasticity keeps fatigue loading for the stud and insert low relative to the applied loading

5. Preload Continued • Belleville washers guarantee maintenance of preload in the event of unanticipated strain • The washers have a stiffness equivalent to that of the stud • Total washer deflection = .026” • With a strain as high as .010” washers will prevent preload from dropping below 3,900 lbf. (The washer and the stud each relax .005”) • Studs to be pre-tensioned with a hydraulic puller to eliminate stored torque along the length of the stud.

6. Flag HardwareINSERT

7. TapLok Threaded Inserts • A “TapLok” 3/8-16 “Medium Length” insert is used (OD into copper is .50”) • Loading: • The stud preload of 5,000 lbf results in 11,800 psi in shear at the outer threads of the insert into the copper. • Thermal + Mechanical loading adds a cyclic load of 1,800 psi • Per the inspection certification the Cu Tensile strength = 38 kpsi and Yield strength = 36 kpsi. • Values of 34 kpsi used for yield to account for observation of slight degradation to hardness after thermal cycling

8. Flag Stud Insert Loading & Stress Summary

9. Modified Goodman Diagram for Insert in Copper Conductor

10. Testing Reinforces Analysis • Ultimate shear strength used in analysis is 22 kpsi, lowest pull out force of 11,000 lbf from testing is equivalent to 27 kpsi shear. Testing verifies values in analysis are conservative • Cyclic testing at 50,000 cycles did not result in any degradation to pull out strength for the test samples • Samples survived tests at 2x fatigue stress at 50,000 cycles

11. Flag HardwareSTUD

12. Flag Stud Loading • A preload of 5,000 lbf is applied with an equivalent stress of 64,900 psi • Thermal loading after ratcheting of the flag temperature applies an enforced deflection of .0043 inches • Thermal ratcheting +mechanical loading adds 9,800 psi

13. Flag Stud Loading & Stress Summary • With the 5,000 lbf preload and the thermal loading applied the stud sees a max stress of 74.7 ksi • The ultimate tensile strength for the Inconel 718 stud is 210 ksi and the yield strength is 185 ksi

14. Modified Goodman Diagram For Stud

15. Shear Key Hardware Threads

16. Shear Key, Threaded Copper • Unlike the Flag studs the Shear Key bolts have more depth of copper available (and less width) so no inserts are used • Testing indicated similar pullout strength for the deeper tapped holes without inserts • Analysis indicates adequate shear area for both cyclic and static loading • Analysis indicates strength is adequate to survive off normal conditions

17. Shear Key Thread Load & Stress Summary

18. Modified Goodman Diagram for Shear Key Bolt in Copper Conductor

19. Shear Key Hardware Bolts

20. Shear Key, Bolts • Custom compression washers are used to maintain preload. Provides .007” deflection • Use of Inconel 718 Bolts ensures large safety margins even with loss of preload and without friction

21. Shear Key Bolt Loading & Stress Summary

22. Modified Goodman Diagram for Shear Key Bolt

23. Summary, Acceptance Criteria • As plotted against the 20x life fatigue curve nominal design points fall within acceptable fatigue stress limits for inserts and copper threads. • Copper threads and Inserts were tested at 2x nominal design cyclic stress values at 50,000 cycles (1 x life) or greater with no failure • Static stress values fall at about 2/3 yield for stress in the copper threads and inserts and at less than half of the tested mean shear failure strength • Analysis and testing predict no failure in the copper threads for the off normal conditions presented • Stress values for the Inconel Shear Key Bolts and Flag Studs have much larger margins of safety for all of the above criteria