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

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

Flag Hardware Exploded View

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

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.

Flag Hardware INSERT

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

Flag Stud Insert Loading & Stress Summary Stud Nominal Loading Stud Nominal Loading + Thermal Insert Cyclic Test Insert Cyclic Test 2x Stress Axial Preload lbf5000 Cyclic Axial Loading lbf Maximum Axial Load Cu Thread Preload Stress11765 Cu Thread Cyclic Axial Max Stress Cu Thread Static Factor of Safety

Modified Goodman Diagram for Insert in Copper Conductor

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

Flag Hardware STUD

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

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 lbf5000 Cyclical Axial Loading lbf Maximum Axial Load Stud Preload Stress64935 Stud Cyclical VonMises Stress Stud Static Factor of Safety VonMises

Modified Goodman Diagram For Stud

Shear Key Hardware Threads

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

Shear Key Thread Load & Stress Summary 45 Deg. Bolt Frictionless Case Vertical Bolt Frictionless Case 45 Deg. Bolt.2 Friction Vertical Bolt.2 Friction 45 Deg. Bolt.4 Friction Vertical Bolt.4 Friction 45 Deg. Bolt.4 Friction No Preload Cyclic Test Conditions Axial Preload lbf Resultant Cyclic Axial Load lbf Maximum Axial Load lbf Cu Thread Preload Stress psi Cu Thread Cyclic Axial Max Stress psi Cu Thread Static Factor of Safety

Modified Goodman Diagram for Shear Key Bolt in Copper Conductor

Shear Key Hardware Bolts

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

Shear Key Bolt Loading & Stress Summary 45 Deg. Bolt Frictionless Case Vertical Bolt Frictionless Case 45 Deg. Bolt.2 Friction Vertical Bolt.2 Friction 45 Deg. Bolt.4 Friction Vertical Bolt.4 Friction 45 Deg. Bolt.4 Friction No Preload Cyclic Test Conditions Axial Preload lbf Resultant Cyclic Axial Load Maximum Axial Load Bolt Preload Stress N/A Bolt Cyclic Axial Max Stress N/A Bolt Static Factor of Safety (Von Mises) N/A

Modified Goodman Diagram for Shear Key Bolt

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