GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 1 GLAST Large Area Telescope: Mechanical Systems Peer Review March 27, 2003 Section 7.1 – Stress Analysis Marc Campell SLAC Mechanical Systems Mgr. Gamma-ray Large Area Space Telescope

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 2 Topics Agenda Cal-Grid interface load recovery Grid Stress analysis Radiator Mount Bracket analysis Further work

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 3 CAL Interface Load Recovery CAL-Grid bolted friction joint –1152 screws (72 per CAL module) –Joint allows CAL bottom plate to stiffen LAT by closing out bottom side of Grid Load recovery –Interface loads are backed out from the FEA model by resolving nodal forces at the interface into shear and normal loads at the bolt locations –Required friction coefficients are generated, given a set screw preload and a perimeter backing strip –EM bolted joint tests are underway to validate friction coefficient and joint behavior Histogram Showing Required Friction Coefficients Qual Friction Coefficients for CAL-Grid Joint

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 4 SC Interface Friction Coefficient Data for Bay 13 With Perimeter Backing Plates

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 5 Grid Stress Analysis Grid stress analysis indicates positive margins of safety for all regions Highest stresses occur in transition regions around SC mount –Nominal maximum Von Mises stress is order of magnitude below yield for material –Large corner radii in the actual design, not included in the model, limit stress risers –Top flange in model has a weighted-average cross section which is no more than twice the minimum cross sectional area Grid material properties –Material: 6061-T6 aluminum (6061-T651, stress-relieved, then heat- treated during fabrication) –Sy = 240 MPa (35 ksi) –Su = 290 MPa (42 ksi) Factors of safety (per NASA-STD-5001) –Metallic structures Yield: FS y = 1.25 Ultimate: FS u = 1.4

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 6 Grid Stress Analysis MSy = Sy/( 1.25  i ) –1 MSu = Su/( 1.4  i ) –1

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 7 Grid Internal Stresses Grid internal bending stresses are low, as indicated in contour plots Y-Direction Direct Stress in Web Near Grid Center for MECO Case Y-Direction Direct Stress in Web Near +Y SC Mount for Lift-Off/Airloads Case lat9ol7 lat9ol6

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 8 Grid Stresses Near SC Mount Boss Von Mises Equivalent Stress for MECO Case Von Mises Equivalent Stress for Lift-Off/Airloads Case lat9ol7 lat9ol6

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 9 Radiator Mount Bracket Analysis Design Loads and critical load cases Loads defined in Environmental Spec –FS=1.25 (PFQ) used for launch loads –FS=1.40 used for lift case Assume Observatory lift load is carried in 2 of 4 fittings Critical Load Cases Studies

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 10 Finite Element Model: Parameters and Assumptions Mass Properties –MSS States Maximum Observatory mass of 4627 kg + PAF –Bracket mass calculated to be 5.56 kg Material Properties –AL 6061-T6 Elastic Modulus = 68.9 GPa (10 Msi) Poisson’s Ratio = 0.33 Density = 2710 kg/m 3 (0.10 lb/in 3) Yield Stress = 241 MPa (35 ksi) Shear Ultimate = 145 MPa (21 ksi) Bearing Yield = 345 MPa (50 ksi, 1.5 e/d)

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 11 Results – Stress Contours: Case +X / -Z Load Max Von Mises Stress =17.0 MPa (2.46 ksi) (Uncertainty = 2.0) Material Yield =241 MPa (35.0 ksi) M.S. = 13.2

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 12 Results – Stress Contours: Case -X / -Z Load Max Von Mises Stress =18.1 MPa (2.62 ksi) (Uncertainty = 2.0) Material Yield =241 MPa (35.0 ksi) M.S. = 12.4

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 13 Results – Stress Contours: Case +Y / -Z Load Max Von Mises Stress =8.6 MPa (1.24 ksi) (Uncertainty = 2.0) Material Yield =241 MPa (35.0 ksi) M.S. = 28.2

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 14 Results – Stress Contours: Case -Y / -Z Load Max Von Mises Stress =6.6 MPa (0.96 ksi) (Uncertainty = 2.0) Material Yield =241 MPa (35.0 ksi) M.S. = 36.5

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 15 Results – Stress Contours: Case +Z Lift Load Max Von Mises Stress =188.9 MPa (27.4 ksi) (Uncertainty = 2.0) Material Yield =241 MPa (35.0 ksi) M.S. = 0.28

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 16 Results – Loads and Stresses at bolt locations

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 17 Summary of Margins of Safety Tension Failure Bearing Failure Tear Out Failure

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 18 RMB Conclusions Lift case induces the highest stresses Margins of safety are good for all design cases Calculated stiffness is high, which is conservative for loads determination The radiator attachment bracket meets or exceeds all design requirements

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 19 Summary and Further Work Summary –Integrated LAT structural analysis results of the static- equivalent load cases indicate that LAT deflections and stresses are within required limits –Grid stress analysis shows that the Grid design is not highly-stressed, but driven more by the natural frequency requirement Further work –Finalize design of the SC mount region with the SC contractor and complete stress analysis –Complete stress analysis on EMI skirt pieces

GLAST LAT ProjectDOE/NASA Mechanical Systems Peer Review, March 27, 2003 Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 20 End of Section 7.1 Section 7.1