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Component Testing. Test Setup TapLok Insert Shear Key Copper Threads Friction Tests Collar Shear Tests. NSTX TF FLAG JOINT REVIEW 8/7/03. Michael Kalish. TapLok Threaded Inserts. A “TapLok” 3/8-16 “Medium Length” insert is used (OD into copper is .50” (OD = .562”, length = .562”) )

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Component testing
Component Testing

  • Test Setup

  • TapLok Insert

  • Shear Key Copper Threads

  • Friction Tests

  • Collar Shear Tests

NSTX TF FLAG JOINT REVIEW 8/7/03

Michael Kalish


Taplok threaded inserts
TapLok Threaded Inserts

  • A “TapLok” 3/8-16 “Medium Length” insert is used (OD into copper is .50” (OD = .562”, length = .562”))

  • Loading:

    • The stud preload of 5,000 lbf results in 11,800 psi (10,069 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. Material: C10700 Silver Bearing Copper , Hard Drawn (50% Cold Worked)

  • Values of 34 kpsi used for yield to account for observation of slight degradation to hardness after thermal cycling


Cyclic testing taplok
Cyclic Testing, TapLok

  • Using same test setup medium length (.562”)Tap Lok inserts were cycled then pulled

  • Test sample was heated to 100 C during cycling

  • Six test pieces were cycled at 5,000 to 6,000 lbf for 50,000 cycles or greater

    • Test levels reflect the 1,000 cycle thermal loading case

    • Cycled with 1 Hz Sine Wave

  • Two samples were cycled at 5,000 to 7,360 lbf to test at the 2x Stress at design life condition

  • After cycling static pull tests determined if pull out strength had degraded


TapLok Static Pull Test Results

  • Average pullout force for .562” TapLok was 12,700 lbf corresponding to a calculated ultimate shear stress of 29.9 KPSI (25.6 KPSI)

  • This value derived from the test data is 36% (17%) higher than the assumed ultimate strength in the fatigue analysis and twice the design load


Results cyclic pull tests for taplok
Results Cyclic Pull Tests for TapLok

  • No Failure of any sample including two samples cycled at 2x Stress and 50,000 cycles (5,000 lbf to 7,360 lbf)

  • Pull out strength relatively unchanged for samples cycled at design loads

  • Yield strength values averaged 82% of Tensile strength

  • Samples cycled at temperature did not vary from unheated samples


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


Fasteners joint design
Fasteners / Joint Design

Michael Kalish

NSTX TF FLAG JOINT REVIEW 8/7/03



Flag stud loading
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



Stud preload
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


Minimum Contact Pressure

5.00 in

11.00 in

Width - W = .79 in; Bolt Hole Dia. = .406 in

Contact Area - AC = .79 in x 5.00 in – 4 (π x (.406 in)2)/ 4 = 3.434 in2

Bolt Pretension Force – FPRE = 4 x 5000 lbf = 20000 lbf

Minimum Force - FMIN = 4 x 3300 lbf = 13,200 lbf

Pretension Contact Pressure – PPRE = FPRE/ AC = 5843 psi

Minimum Contact Pressure - PMIN = FMIN/ AC = 3846 psi (without Belleville washers)


Leverage previous design experience
Leverage Previous Design Experience

  • Flag Material: C10700 H002, Silver Bearing Copper, Half Hard. Keep copper thread shear stress below 11,800 psi to eliminate need for retesting.

  • Tap-lok inserts: Use longest insert possible for given size.

  • Stud Material: Inconel 718. Pretension much less than .75 yield strength (copper thread shear stress dominates).

  • Use Belleville washers and/ or Direct Tension Indicating (DTI) washers to monitor bolt pretension, reduce cyclic stress amplitude, and maintain bolt tension with thermal cycling and creep.

  • Bolts loaded in tension only: separate shear load and compression load functions (rely on friction or separate feature to take shear load).

  • Monitor joint electrical contact resistance.


NSTX Update Design

Tap-Lok Inserts


NSTX Update Design

Tap-Lok Inserts


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