NSTX TF Flag Joint Torque Collar Chit Review C Neumeyer 9/11/3

BACKGROUND Four chits from the August 7 review expressed concern regarding the torque collar design… TITUS: The shear capacity of wet lay-up is based on test and a fine mesh model. Either Irv should have a local model with a similar fine mesh or the 1.6 factor from the test FEM should be ignored. NELSON: Concern about welding ears to torque collar – distortion, heating, etc. Suggest mock-up to confirm feasibility. NELSON: Concern is shear lag at gaps. Recommend analysis of current design and continuous design, thicker bond line, more gaps, etc. ANDERSON: Build mock-up of collar and test for shear failure due to temperature and torsion.

Initiated FEA of collar… -discovered problems not only with shear lag at gaps but also stress concentrations and excessive variations in compression due to lack of vertical symmetry FEA Model of August 7 Collar Design

Pursued several variants before arriving at a design which…. fits in the available space can be installed despite the limited access allows access to the box bolts limits shear in wet lay-up to acceptable values - analysis and testing not yet finalized Latest Design Keys for torsion, free for vertical and Radial motion Inconel Struts Threaded Connectors Anchor Bushings Anchor Pins

In parallel, FEA cases have been run for collar-less design -no significant structural impact in removing collar -changes in joint pressure and resistance pattern result in a shift in the current distribution, but temperature impact is not severe -peak temperature at joint ~ 10 o C higher than cases with collar Review of original FEA indicates that collar benefit to turn-turn insulation shear is not required to meet allowable -collar reduces peak insulation shear by 17% -Peak shear under worst case conditions without collar would increase from 2.2 to 2.7ksi -Allowable is 2.9ksi which includes a safety factor of 2 against R&D tests at 600psi compression

Analysis shows that collar-less design meets all requirements Advantages of Collar… 10 o C peak temperature benefit 17% turn-turn shear stress benefit Restraint against clocking of bundle, in addition to friction Disadvantages of Collar… Additional complexity of assembly Reduced access to box bolts Thermal induced stresses Potential cost/schedule risk

NEW STRATEGY… 1)Continue design/analysis/test of collar and bring to closure 2)Do not implement collar initially, except for anchor pins 3)Perform measurements during next run to confirm analysis Operations to be initiated at low Bt (~ 3kG) Level to be increased only as justified by measurements 4)Implement collar in future if measurements are not favorable

PURPOSE OF REVIEW Obtain critique of collar-less strategy Preview new collar design but defer review to a later date if necessary

ANALYSIS OF SOFT COLLAR-LESS CASE Caselost contact area <1000 psi contact pressure 6kG w/collar4%9% 6kG w/o collar15.6%21.3%

PRESSURE & RESISTIVITY WITH COLLAR Note: Data interpolated from uniform pressure during rampup to SOFT and during Flattop, then held fixed at EOFT values thru EOP

PRESSURE & RESISTIVITY W/O COLLAR Note: Data interpolated from uniform pressure during rampup to SOFT, then held fixed at SOFT values thru EOP SOFT assumption is conservative

Add 15 o C For Bolt Hole Effect, Tmax = o C

With CollarWithout Collar Note: Contour values not equal CURRENT REDISTRIBUTION Current finds path of least resistance Much of joint is inactive

SUMMARY Design meets allowables without collar -Conservativism still remains All PF coils at max current for full time duration 0.7 sec flat top T=120 o C Collar increases margins, but adds risk and complexity Strategy to defer collar is the best to pursue at this time

NEW COLLAR STATUS Design is in-hand -Fabrication drawings being generated from Pro-E CAD model Analysis is essentially complete - SOFT, EOFT, EOP cases - Safety factor calculation based on extrapolation up to ~ 8ksi of shear strength from prior database with compression up to 2ksi Testing is underway to determine wet lay-up shear at high compression

NEW COLLAR DESIGN

FEA OF NEW COLLAR DESIGN Scotchply & CTD Hysol Insulation 3-total applied Torque =0.25M lb-inch angular motion fixed

Compression Twist Shear (Torque) Axial Shear (Thermal) Combined Shear TYPICAL FEA RESULT (SOFT)

SAFETY FACTOR CALCULATION Shear_VectorSum = {(Shear_angular) 2 + (Shear_long) 2 } 0.5 Shear_Allowable = 28MPa(4ksi) + 1.3*|Compression| Safety_Factor = Shear_Allowable / Shear_VectorSum

FEA SUMMARY TABLE Pressure on insulation angular shear on insulation z-direction shear on insulation Safety factor with compress. dT=17 degree with Torque 0.25M[lb-inch] 4~57MPa (0.6~8.1ksi) ave. ~25MPa 15MPa (2.1ksi) 5MPa (0.7ksi) 2.6 dT=54 degree with Torque 0.25M[lb-inch] 9~52MPa (1.3~7.4ksi) ave. ~25MPa 29MPa (4.1ksi) 14MPa (2.0ksi) 1.8 dT=72 degree without Torque 11~45MPa (1.6~6.4ksi) ave. ~25MPa 28MPa (4ksi) 18MPa (2.6ksi) 1.9