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”))

• 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

• 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

Un-Cycled Sample Break Force

TLC-1 14500

TLC-2 12500

TLC-3 12500

TLC-4 11500

TLC-5 12500

Average = 12700

Tap Loc 3/8-16 Thread Strength

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8 13

Sample

Fo

rce

lb Un-Cycled Break

Average Un-Cycled

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

• 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

Tap Loc 3/8-16 Thread Strength

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Sample

Fo

rce

lb

Un-Cycled Break

Cycled Break

Average Un-CycledLinear (AverageCycled)

Cycled Sample

Break Force

Yield Force

Cycle Load Low

Cycle Load High Cycles

TL1-1 5000 5952 50000TL1-3 12120 9380 4998 5968 50000TL2-1 12250 10880 5000 5980 50000TL2-2 12620 10500 5000 5960 50000TL2-3 13260 11000 5020 5980 50000TL2-4 13880 11120 5000 6000 223860

Average = 12826 10576 5003 5973 78977

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

 

Stud Nominal Loading

Stud Nominal Loading + Thermal

Axial Preload lbf 5000 5000

Cyclical Axial Loading lbf 200 755

Maximum Axial Load 5200 5755

     

Stud Preload Stress 64935 64935

Stud Cyclical VonMises Stress 67532 74740

Stud Static Factor of Safety VonMises 2.74 2.48

Fasteners / Joint Design

Michael Kalish

NSTX TF FLAG JOINT REVIEW 8/7/03

Modified Goodman Diagram for Insert in Copper Conductor

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Mean Stress (kpsi)

Fa

tig

ue

Str

es

s A

mp

litu

de

(k

ps

i)

Ultimate Shear

.577x Tensile Yield

StressAmplitude x 2.5

Mean Stress

Beneath Bold Lines RepresentsAcceptance Criteria

Pull Testing Indicated Failureat 27,000 psi

Nominal Stress Values(50,000 Cycles)

Stress Values with Flag Thermal (1,000 Cycles)

As Tested at 50,000 Cycles

As Tested >2x stress at 50,000 Cycles

.577xYield

10^6 Cycles

20,000 Cycles

`

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

Modified Goodman Diagram For Stud

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Mean Stress (kpsi)

Fat

igu

e S

tres

s A

mp

litu

de

(kp

si)

Ultimate Tensile

S.e Infinite life

Yield Strength

StressAmplitude x 2.5

Mean Stress

Mean Stress = 69,840 psiStress Amplitude = 4,900 psi

Beneath Bold Line RepresentsAcceptance Criteria

YieldStrength

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 0

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Load vs Deflection for Stud and Cu Flag

Stud Extension Flag Compression

AppliedLoad3,300 lbs

AdditionalBolt Loading300 lbs

Slope representsElasticity of Stud

Slope RepresentsElasticity of Cu Flag

Forcelbs

Inches x 10^-3

Minimum Contact Pressure

11.00 in

5.00 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

• 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 DesignTap-Lok Inserts

NSTX Update DesignTap-Lok Inserts