Fasteners / Joint Design

1. Fasteners / Joint Design NSTX TF FLAG JOINT REVIEW 4/10/03 Michael Kalish

2. Stud Preload • Maintaining the preload on the stud is critical for maintaining contact pressure and contact resistance • Using a long narrow bolt results in a much higher bolt elasticity than that of the Flag (10X). • Applied cyclical loading adds relatively small additional loading to the stud. • With higher elasticity, loss in preload due to deflection is minimized.

3. Preload Continued • Belleville washers are used to account for any unexpected yielding of bolt or copper • While the bolt length provides adequate elasticity to accommodate design load scenarios the addition of Belleville washers prevents relief of the preload in the event of unanticipated strain • Washer has ½ the stiffness of the bolt, for every .001 inch strain only 125 lbf preload is lost (total washer deflection = .032”) • With a strain as high as .008” washers will prevent preload from dropping below 3,560 lbf. (the first .0045” drops the bolt pre-load to 4,000 lbf then the washer takes over) • Testing of prototype will verify that preload is maintained. • A washer plate is added to spread out the compressive forces under the nut and minimize local yielding of the copper. • Bolts to be pre-tensioned to eliminate stored torque

4. Bolt Characteristics • “Bolt” is a a 3/8”-16 stud threaded at both ends • To increase elasticity the bolt shank diameter will be just slightly larger than the root diameter of the threads resulting in a relatively elastic bolt (a creep of .001” results in a loss of 225 lbf of preload) • Loading: • A preload of 5,000 lbf is applied with an equivalent root diameter stress of 64,700 psi • Thermal loading after ratcheting applies an enforced deflection of .0043 inches corresponding to a stress adder of 12,700 psi • As a result of stiffening the hub structure additional mechanical loading is minimal so that almost all fatigue loading is the result of thermal stress • With the 5,000 lbf preload and the thermal stresses applied the bolt sees a mean tensile stress of 71.2 ksi and a mean amplitude of 6.5 ksi • The ultimate tensile strength for the A286 is 145 ksi and the yield is 100 ksi

5. Modified Goodman Diagram For A286 Stud

6. Threaded Insert • A “TapLok” 3/8-16 “Medium Length” insert is used (OD into copper is .50”) • Loading: • The bolt preload of 5,000 lbf results in 11,800 psi in shear at the outer threads of the insert into the copper. • Thermal loading adds a cyclical load of 2,300 psi • Additional mechanical loading is minimal so that almost all fatigue loading is the result of thermal stress • Per the inspection certification the Tensile strength = 38 kpsi equivalent to a Shear Strength = 22 kpsi • With the 5,000 lbf preload and the thermal stresses applied the bolt sees a mean shear stress of 12.9 kpsi and a mean cyclical amplitude of 1.2 ksi

7. Modified Goodman Diagram for Insert in Copper Conductor

8. Threaded Insert (cont.) • Testing shows margins may be greater then the numbers indicate. The lowest pull out force measured = 11,500 lbf equivalent to 27 kpsi shear strength in the copper (as compared to 22 kpsi) • The insert was tested for both pull out strength and pull out strength after cycling • Cycling (one sample) did not indicate significant degradation to pull out strength (fatigue sample pulled at 12,380 lbf) • Further testing is planned. A mechanical prototype will test for maintenance of preload after application of a cyclical load.

9. Testing NSTX TF FLAG JOINT REVIEW 4/10/03 • Test Setup • Pull Tests • Cyclical Pull Testing • Friction Tests • Collar Shear Tests • E-Beam Weld Tests • Mechanical Prototype Michael Kalish

10. Test Setup • MTS Hydraulic Test Stand • Plots Load vs Deflection up to 100,000 lbf • Provides Cyclical Testing Capabilities

11. Designed to test pull out strength of inserts Inserts installed in spare lengths of conductor Keenserts and two lengths of Taplok inserts tested Pull Test Setup

12. Specimen in Test Fixture Pull Test Setup (cont.)

13. Pull Test Results KeenSerts • KEEN SERT #1     11,120lbs • KEEN SERT #2     12,000lbs • KEEN SERT #3     11,880lbs • KEEN SERT #4     11,620lbs • KEEN SERT #5     11,500lbs • KEEN SERT #6     11,260lbs • KEEN SERT #7     11,500lbs • KEEN SERT #8     11,380lbs

14. Pull Test Results Tap-Lok • 3/8-16 H Series Tap-Lok Inserts • 1st Sample SUMMARY (peak force) Regular Length 0.687”, Tap Drill • TAP LOK #1 15,260lbs • TAP LOK #2 15,500lbs (bolt broke) • TAP LOK #3 15,260lbs (bolt broke) • 2nd Sample SUMMARY (peak force) Regular Length 0.687”Tap Drill Plug Tapped Only • TAP LOK #1 16,000lbs • TAP LOK #2 15,380lbs • TAP LOK #3 15,760lbs • TAP LOK #4 15,500lbs • TAP LOK #5 15,620lbs • 3rd Sample SUMMARY (peak force) Medium Length 0.562”, Insert Tool Only • TAP LOK #1 12,500lbs • TAP LOK #2 12,500lbs • TAP LOK #3 11,500lbs • TAP LOK #4 12,500lbs • TAP LOK #5 11,760lbs Displacement vs Force Curve for Tap Lok #4, 3rd Sample Peak Force = 12,500 lb

15. Cyclical Testing, Pull Out • Using same test setup medium length Tap Lok insert was cycled then pulled • 5000 cycles at 4600 lbf to 6000 lbf • 45000 cycles at 5400 lbf to 6000 lbf • Cycled at 1 Hz Sine Wave • Ranges represent thermal + operational loads for 25 degC and 5 degC cyclical thermal loading • Sample pulled after subjected to Fatigue along with insert installed in same conductor piece.

16. Cyclical Testing Results • Shaded area may indicate drift or creep (first run exhibited a “negative creep” drift) • Worst case creep of .0025”(if real) • Top Plot5,000 cycles at 4,600lbf to 6,000lbf • Bottom Plot45,195 cycles at 5,400lbf to 6,000lbf

17. Cyclical Testing Pull Out Result • Fatigued Insert Pullout (bottom trace) vs Unfatigued Insert Pullout(top trace) • Fatigued = 12,380 lbf • Unfatigued = 13,380 lbf • Previous samples showed scatter of 11,500 lbf to 12,500 lbf • Pull out strength relatively unchanged • More testing to follow

18. Friction Test Setup • Two horrizontal load cells measure compressive force provided by eight 3/8th inch bolts • Specimens are machined and plated after each run • Vertical load is applied to offset middle block

19. Friction Test Calibrations • The two compression loads cells were checked against the MTS vertical load cell and found to be to within .30%

20. Friction Tests Results • Force is recorded at point where “inelastic” behavior begins • Initial testing of unplated copper resulted in COF = .12 • Testing of plated copper increased COF values to .41

21. Friction Test Results (cont.) • Mean COF = .41 • Min. Value = .39 • Results consistent for varying compressive loads • Testing to continue • Will explore improvement of COF by changing surface conditions

22. Representative sample of collar arrangement fabricated to characterize elasticity and shear strength Collar Shear Test

23. Collar Shear Test Results • No compressive load was applied • Shear area approx. = 11.8 sq in. • For lower values split occurred on one side. For higher values on both sides simultaneously • Separation occurred at epoxy to SS interface. • Further testing planned for improved samples • SUMMARY: #1 60,000lbs, 2,540 psi #2 58,590lbs, 3,000 psi #3 43,100lbs, 1,820 psi #4 40,000lbs, 2,040 psi #5 61,900lbs, 2,610 psi #6 65,000lbs, 2,720 psi

24. E-Beam Weld Test Specimens • Tensile Testing performed on 1” x .50” EBeam welded copper bars

25. E-Beam Weld Test Specimen Results • SUMMARY “3L” Peak Force 13,760lbs, 27,520 psi “3R” Peak Force 13,260lbs 26,520 psi “4L” Peak Force 13,120lbs 26,420 psi “4R” Peak Force 14,380lbs 28,760 psi Copper Bar Weld “4R” Peak Force 14,380lbs, Peak Displacement .199”

26. E-Beam Weld Test Specimen Results • Bars separated at weld although weld area looked entirely homogeneous

27. Mechanical Prototype Testing • A prototype of the flag bolted to a section of conductor is in fabrication. • Vertical loading will be applied directly to the flag • This mockup will test the bolted joint for maintenance of preload after cycling. • Contact resistance will be monitored in real time.