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NCSX Modular Coil Joint Load/Stress Calculation

NCSX Modular Coil Joint Load/Stress Calculation. By Leonard Myatt Myatt Consulting, Inc. The Big Picture. Estimates of Bolt Loads with Bonded Flange Interfaces need to be checked. MC Global model already quite big.

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NCSX Modular Coil Joint Load/Stress Calculation

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  1. NCSX Modular CoilJoint Load/Stress Calculation By Leonard Myatt Myatt Consulting, Inc.

  2. The Big Picture • Estimates of Bolt Loads with Bonded Flange Interfaces need to be checked. • MC Global model already quite big. • Need to develop a simple bolt model with properties (shear & tensile stiffness) similar to the reference joint designs. • Apply approximation to MC Global model to determine bolt load distribution. MC Joint Analysis

  3. Process Overview • Import Joint Models from ORNL into ANSYS: • “Joint1” (Double nut on Stud) • “Joint2” (Bolt & tapped flange hole) • Apply symmetry, add 30 mil Stycast gap, add general contact at flange-shim interface • Loading: • Impose lateral deformation (parallel to flange face) • Impose axial deformation (parallel to bolt axis) • Response: • Lateral force and joint stiffness v. imposed deflection. • Axial joint stiffness (single-value per joint configuration). MC Joint Analysis

  4. Process Overview, cont’d • FYI: Report stresses for 25 k-lb lateral load. • Develop simplistic equivalent bolt model for Global MC simulations. • Incorporate simplistic bolted connection model into Global MC simulation. • Analysis Units: • Bolted Joints use English units. • Global MC uses SI units. MC Joint Analysis

  5. Reference Design(Courtesy D. Williamson) Joint2 Expected 30 mil Annular Gap at Flange Through-Hole Not Shown Joint1 MC Joint Analysis

  6. Set Preload to ~73 k-lbf NASA Technical Memorandum 106943 used to define Preload Spec http://gltrs.grc.nasa.gov/reports/1995/TM-106943.pdf MC Joint Analysis

  7. ANSYS Model, Joint1 MC Joint Analysis

  8. ANSYS Model, Joint2 MC Joint Analysis

  9. Joint1 Bolt Preload Nominal Preload ~50 ksi MC Joint Analysis

  10. Joint2 Bolt Preload Nominal Preload ~50 ksi MC Joint Analysis

  11. Joint1 Force, Deflection & StiffnessPreload + Transverse Motion MC Joint Analysis

  12. Joint2 Force, Deflection & StiffnessPreload + Transverse Motion MC Joint Analysis

  13. Joint1 Contact Stress (S3)G11 & Stycast Insulating Parts Stress & Force Vectors, 25000 lb Shear Load MC Joint Analysis

  14. Joint1 Bolt Tension Stress (S1) Stress from 25000 lb Shear Load MC Joint Analysis

  15. Joint2 Contact Stress (S3)G11 & Stycast Insulating Parts Stress & Force Vectors, 25000 lb Shear Load MC Joint Analysis

  16. Joint2 Bolt Tension Stress (S1) Stress from 25000 lb Shear Load MC Joint Analysis

  17. Tensile Stiffness of Joints 1&2 • Apply axial loading where bolt hardware interfaces with flange face. • Calculate tensile stiffness of each joint. • Stiffness values to be used as basis for developing simplistic joint model for more precise Global simulation of MC structure. MC Joint Analysis

  18. Joint1 Tensile Stiffness~5.4 M-lb/in Check: k(bolt)=AE/L~(1.48in2)(27.6Msi)/6”~7 M-lb/in MC Joint Analysis

  19. Joint2 Tensile Stiffness~8.8 M-lb/in Check: k(bolt)=AE/L~(1.48in2)(27.6Msi)/3.5”~12 M-lb/in MC Joint Analysis

  20. Simple Model of Bolted Joint1 for Equivalent Stiffness Approx. Stiffness Match Achieved with 2.9” diameter Bolt MC Joint Analysis

  21. Simple Model of Bolted Joint2a for Equivalent Stiffness Approx. Stiffness Match Achieved with 2.75” diameter Bolt MC Joint Analysis

  22. A-B Joint Bolt Definition • Bolt layout drawing shows 26 bolts at this A-B flange. MC Joint Analysis

  23. A-B Bolt Types(M. Cole FP-STUDS.PPT) MC Joint Analysis

  24. Bolts 1-9 Defined by Project (M. Cole FP-STUDS.PPT) MC Joint Analysis

  25. Bolts 10-15 Defined by Project (M. Cole FP-STUDS.PPT) MC Joint Analysis

  26. Bolts 16-18 Defined by Project (M. Cole FP-STUDS.PPT) MC Joint Analysis

  27. Bolts 19-26 Defined by Project (M. Cole FP-STUDS.PPT) MC Joint Analysis

  28. Application of Equivalent Stiffness Bolted Joints to Global Model at A-B Flange • Solid PIPE16 elements, with dimensions to match calc’d Joint stiffness, are added to each A-B Bolted connection. MC Joint Analysis

  29. Top 16 Bolted Connections Bolt #11 is questionable MC Joint Analysis

  30. Bottom 10 Bolted Connections Would-be Bolt #16 is missing. MC Joint Analysis

  31. Global Model Analysis Notes • The global model bolt #11 does not appear in the bolt numbering drawing or M. Cole’s pictorial layout. • The global model appears to be missing a bolt (#16 in the bolt numbering drawing). • If global model bolt #11 is eliminated, and a bolt is added to hole #16, then the model would be consistent with other references. MC Joint Analysis

  32. Analysis Notes, cont’d • A significant effort was made to simulate both zero and finite friction A-B joint behavior. • Bolt Preload Load-Step converged OK. • But excessive computer run-time (4+ days for 4% of EM load) lead to an alternative approach for evaluating max bolt shear loads. • The interface is modeled as sliding and always in contact (KEYOPT(12)=4) with zero friction. MC Joint Analysis

  33. Analysis Notes, cont’d • The model converges nicely and produces conservative shear loads for evaluating preload and friction requirements. • However, it does not report accurate tensile loads on the bolts. • We may ultimately need to find a way to run the model with friction or at least open/closed contact behavior (keyopt(12)=0) to confirm preload levels and bolt stresses. (This requires more thought.) MC Joint Analysis

  34. Global Model Results • Bar graph and contour plot of shear load on each A-B bolt. • A-B Interface pressure from EM loads, neglecting bolt preload effects. • A-B Interface relative motion from EM loads, neglecting bolt preload effects. MC Joint Analysis

  35. A-B Bolt Load Distribution(ORNL reference: fsum_dl-em1.xls) MC Joint Analysis

  36. A-B Bolt Shear Load [N per bolt]Contour Plot Visual MC Joint Analysis

  37. Shear Load Distribution Observations • The missing bolt (would-be #16) forces the nearby bolt (#17) to carry a larger portion of the loading. • The approach used to integrate shear stresses from a bonded analysis over regions of the flange interface (referred to here by the “ORNL” data set) underestimates the shear force distribution compared to this quasi-nonlinear approach. MC Joint Analysis

  38. Shear Load Distribution Observations, cont’d • Adding bolt #16 will surely drop the max shear load on bolt #17, possibly to 12 k-lbf. • However, the load on bolt #26 will likely be unaffected by the change and must carry almost 16 k-lbf. • Applying a reference preload of 73 k-lbf and using friction to carry the shear force will require a minimum friction coefficient, μ, of 16k/73k or 0.22. This correctly assumes that EM loads do not diminish the contact pressure around this bolt (see next slide). MC Joint Analysis

  39. A-B Interface Pressure • The influence of EM Loads on flange face pressure: • increase compression stress in red areas • decrease compression stress in blue areas • Blue means reduction in preload which will diminish frictional capacity of bolted joint. • Notice inboard leg interface predominantly in compression and may carry shear stress (analysis TBD). MC Joint Analysis

  40. A-B Interface Slip (No Friction) • Plot shows influence of EM Loads on flange face relative motion (slip). • In bolt region, relative motion <8 mils, and higher near #24. • In unbolted Inboard Leg region, relative motion 37 mils max. MC Joint Analysis

  41. Bolt Stress Observations • If the stabilizing effects of friction are conservatively ignored, then the transverse joint loads (F) must be carried by the bolting hardware & insulation. • Stresses can be estimated by scaling the bolt tension and insulation compression by (F/25k) from the plots presented above. • F=16k-lbf at #24 would result in: • A bolt tensile stress of (124ksi)(16/25)=79 ksi plus a thread concentration factor. • An insulation stress of (-45ksi)(16/25)=29 ksi in Stycast (which has an ultimate strength of <20 ksi, ref. Freudenberg test data) • Therefore, the present design will need to rely on friction. MC Joint Analysis

  42. Conclusions • Two prototypical MC bolted connections are modeled, analyzed and characterized. • A simplistic approximation is developed and incorporated into the global MC model. • Complexities of modeling a friction interface are compounded by the size of the global model and force a more efficient approach: • Contact at A-B only with zero friction & zero separation. MC Joint Analysis

  43. Conclusions • This approach produces conservative shear loads on each A-B bolt (not diminished by friction), and provides a benchmark for earlier calculations which assumed a bonded interface condition. • These earlier results appear to be non-conservative by as much as 2x, and miss a peak A-B shear load of ~16 k-lbf. MC Joint Analysis

  44. Conclusions • Unprotected by the isolating effect of a preloaded frictional joint, the bolt and Stycast would exceed reasonable stress limits with such a shear force. • Assuming a modest friction coefficient of 0.22, the friction developed by the preloaded joint would completely isolate the bolt and Stycast from this shear load. Other bolts should also be checked as local normal stresses may reduce the interface pressure and diminish the joint’s ability to carry the shear in friction. MC Joint Analysis

  45. Conclusions • A more thorough analysis of the interface still requires a traditional [nasty] contact analysis where flange separation can occur. • Such an analysis will do a better job at determining the variation in bolt tension stresses and interface pressure with EM loading. • Analyses by others indicate that A-A may be a more heavily-loaded connection, and therefore should be evaluated ASAP. MC Joint Analysis

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