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NSTX TF Flag Joint Review ANALYSIS & DESIGN C Neumeyer 9/3/3. Topics. Backround Requirements Forces and Load Paths Thermal Effects Contact Resistance Features of New Design Performance of New Design. BACKGROUND. TF joint failed on February 14, 2003 due to structural weaknesses
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Topics • Backround • Requirements • Forces and Load Paths • Thermal Effects • Contact Resistance • Features of New Design • Performance of New Design
BACKGROUND • TF joint failed on February 14, 2003 due to structural weaknesses • Project has developed a more robust design....... • factor in lessons learned from failure • all engineering aspects analyzed at appropriate level of detail • testing as necessary for engineering input and design verification • reduced dependence on precision manufacturing/assembly • easier maintenance
DESIGN 3D modeling complete, including… • integrated TF inner leg bundle • coolant tube routing and bulkhead • outer leg connections Fabrication drawings complete, including… • conductors • flags • flag boxes • shear shoes • hub assembly • torque collar* * Under revision
ANALYSIS Structural FEA complete, including… • both tiers of conductors • out-of-plane load path through spline • collar and wet lay-up representation • in-plane, out-of-plane, thermal loads • SOFT, EOFT, EOP cases • Various off-normal cases • Other analysis complete, including… • force calculations • temperatures, including joint temperature rise • fastener sizing calculations • miscellaneous calculations • Torque Collar analysis continuing
TESTING • Component testing (design input data) consists of: • Pull-out tests on threaded inserts • - one time and cyclic at 100oC • Pull-out tests on bolts threaded in copper • - one time and cyclic • Friction coefficient and electrical resistance tests • Shear tests on torque collar attachment • Status: Complete except more data to be generated for torque collar shear at high compression • Prototype testing (design verification) consists of: • Mechanical mock-up of single joint for cyclic fatigue testing • Electrical mock-up of single joint tested at full current and I2T • Status: In Preparation
CURRENT WAVEFORMS • Engineering design accounts for PS response, inc’l L/R decay in case of fault from Imax • ∫I2T = 6.0 x 109 A2-s for 3kG-4.5s • ∫I2T = 6.15 x 109 A2-s for 6kG-0.6s • Design basis ∫I2T = 6.5 x 109 A2-s which causes adiabatic T of 80oC in Cu • 6kG pulse is most critical for joint since forces are maximum and time for heat diffusion is minimum Short Pulse Long Pulse
NUMBER OF PULSES & THERMAL CYCLES • Assume 50,000 pulse requirement at 6kG • 10 yr*20 week*5day*8hr*6pulse/hr = 48,000 • Highly conservative • NSTX 5yr plan calls for … • 40% @ 3kG (25% EM load) • 40% @ 4kG (44% EM load) • 15% @ 5kG (69% EM load) • 5% @ 6kG (100% EM load) • 100% • Assume 1,000 thermal ratcheting cycles (= number of days) • 10 yr*20 week*5day = 1000 • drives flag fastener fatigue cycle requirement • assuming 12 pulse/hr rate to set thermal ratcheting (conservative)
EM FORCES 148kft-lb 3klb • In-Plane • vertical load and moment • due to magnetic pressure • from self-field • Out-of-Plane • lateral due to ItfxBz(oh&pf) • torsional due to ItfxBr(oh&pf) 2.3klb 4.7klb 9.3klb 40.8kft-lb Notes: All coils assumed at full current, worst case polarity (conservative) Forces equal and opposite on two ends of bundle
FUNCTIONS OF JOINT • Mechanical Function • Preload for High Contact Pressure • Structural Support Against EM & Thermal Loads • Maintain High Contact Pressure • Low Electrical Resistance and Dissipation • Peak Temperature within Limit • Electrical Function
LOAD PATHS Friction Shear Shoe Torque Collar Hub/Spline/VV
THERMAL EFFECTS • Vertical length of inner leg bundle from bottom to top increases by up to 0.35” during a pulse • Vertical length of inner leg from torque collar to top of bundle increases due to inner leg temperature rise, whereas flag and hub remain relatively cool • Radius of inner leg bundle increases bundle increases by approximately 0.006” during a pulse • Flag heats modestly during pulse (T ≈ 5oC) but can ratchet to T ≤25oC at rated duty cycle (conservative), r ≈ 0.005” in length
CONTACT RESISTANCE Tolerable Resistivity ≈ 2.5µΩ-in2 (700psi) Req’d Flat Top Time =0.6 sec Note: assuming constant resistivity along joint
CONTACT PRESSURE & RESISTANCE Rmax Pavg
KEY DESIGN FEATURES Shear Shoe Hub Disks Flag Flag bolts (studs) Flag Box Box Bolts (stud) Torque Collar
TORQUE COLLAR • Prior Design (August 7) • not vertically symmetric • Torque reacted through moment arm • New Design • vertically symmetric • torque reacted tangentially
VOLTAGE PROBES FOR IN-SITU JOINT RESISTANCE MEASUREMENT • • IDI 100526 Coaxial Probe • - commercial spring-loaded probe used in semiconductor test industry • 2 probes per flag, 1 connected to instrumentation, 1 redundant spare • All 72 joints monitored (maintenance @ 200A, real time at full current)
DESIGN HIGHLIGHTS • Solid (not split) flags insulated with 4 layers Kapton, glass wrapped, potted in 304SS boxes • Boxes attached to hub disks using 1/2” studs • Flags attached via 3/8” Inconel studs preloaded to 5000lbf • Shear shoe on outer edge of flags is bolted to ends of inner leg conductor using Inconel bolts, one vertical and one angled for moment reaction • 3-segmenttorque collar w/two 1/2” bolts @ 10000lbf per joint, 0.180” wet lay-up with better type of epoxy (Hysol E-120HP) • Collar transmits torque only to hub structure at 3 anchor points • Redundant voltage probes are located on each side of the flag
FEATURES OF OVERALLFEA MODEL • Includes All Essential Structural Components Contributing To Flag Joint Performance • FLAGS - BOXES • COLLAR - HUBS • CENTER STACK - BOLTS • SPLINES - UMBRELLA • etc. • Models non-linear behavior (friction) • 24 fold symmetry (collar gaps, etc. not modeled)
LOAD CASES EXAMINED • Time Points • START OF FLAT TOP (SOFT) • END OF FLAT TOP (EOFT) • END OF PULSE (EOP) • Conditions • Normal • Off Normal • Low Preload (60%) • High Friction Coefficient • Low Friction Coefficient
FEA USED TO ASSESS STRESSES, DISPLACEMENTS, CONTACT PRESSURES
Temperatures Well Below Limit of 120oC Max Temperature of 94oC Occurs Just After EOFT • Tflat = 0.7sec (vs. 0.6 req’t) • Bolt Holes not exactly modeled (+10oC) • OH constant at max current (-TBDoC) • Insignificant change from constant resistivity simulation Contact Region
OFF-NORMAL CASE: 60% PRELOAD • Peak Temperature ≈ 3oC Higher • Temperature Distribution Different • Current Redistribution Beneficial Notes: Held SOFT pressure conditions after SOFT due to lack of EOFT data Color scales different Normal Off-Normal
TORQUE COLLAR FEA Detailed analysis of prior design revealed high stress concentrations in wet lay-up due to lack of vertical symmetry
NEW TORQUE COLLAR FEA • preliminary results indicate adequate safety margins • work still in progress
All defects contributing to original failure have been addressed
CONCLUSIONS • New Design Corrects All Defects Associated with Original Design • New Design Has Sufficient Margins at 6kG (pending torque collar resolution) • Follow-on Activities Will Increase Confidence • Mechanical Prototype Testing • Electrical Prototype Testing • Instrumentation During Commissioning and Operations • - resistance measurement (200A maintenance and real-time) system • - temperature, strain, displacement)