GLAST LAT Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 1
GLAST Large Area Telescope:GLAST Large Area Telescope:
Mechanical Systems Peer ReviewMarch 27, 2003Section 7.1 – Stress Analysis
Marc CampellSLACMechanical Systems Mgr.
Gamma-ray Large Gamma-ray Large Area Space Area Space TelescopeTelescope
GLAST LAT Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
Document: LAT-PR-0XXXX Section 7.1 Stress Analysis 2
TopicsTopics
Agenda• Cal-Grid interface load recovery• Grid Stress analysis• Radiator Mount Bracket analysis• Further work
GLAST LAT Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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CAL Interface Load RecoveryCAL 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
Bolt Size no. 8 no. 6Mu Mu
4.1g Z + 5.1 g X lat9ol4 0.51 0.576.8 g Z lat9ol7 0.31 0.23
Max Interface Qual Friction Coeff 0.51 0.57
Histogram Showing Required Friction CoefficientsHistogram Showing Required Friction Coefficients
Qual Friction Coefficients for CAL-Grid JointQual Friction Coefficients for CAL-Grid Joint
GLAST LAT Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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SC Interface
Friction Coefficient Data for Bay 13
With Perimeter Backing Plates
GLAST LAT Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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Grid Stress AnalysisGrid 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: FSy = 1.25• Ultimate: FSu = 1.4
GLAST LAT Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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Grid Stress AnalysisGrid Stress Analysis
MSy = Sy/(1.25 i) –1
MSu = Su/(1.4 i) –1
Location of Stress Region FeatureDesign Load
CaseStress
MSy(FSy=1.25)
MSu (FSu=1.4)
Grid perimeter wall near mount boss
38 mm thick reinforced wall above SC MECO 32.0 MPa 500% 547%
Mat'l: 6061-T6 alum mount location 4.6 ksi
Grid web bending stress Grid internal web near centerLift-Off /Airloads 22.0 MPa 773% 842%
Mat'l: 6061-T6 alum 3.2 ksi
Corner of Grid at ACD mountBearing/bending stress at corner tab
Lift-Off /Airloads 12.0 MPa 1500% 1626%
Mat'l: 6061-T6 alum extending out from Grid wall 1.7 ksi
GLAST LAT Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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Grid Internal StressesGrid Internal Stresses
• Grid internal bending stresses are low, as indicated in contour plots
Y-Direction Direct Stress in Web Y-Direction Direct Stress in Web Near Grid Center for MECO CaseNear Grid Center for MECO Case
Y-Direction Direct Stress in Web Near Y-Direction Direct Stress in Web Near +Y SC Mount for Lift-Off/Airloads Case+Y SC Mount for Lift-Off/Airloads Case
lat9ol7lat9ol6
GLAST LAT Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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Grid Stresses Near SC Mount BossGrid Stresses Near SC Mount Boss
Von Mises Equivalent Stress for MECO CaseVon Mises Equivalent Stress for MECO CaseVon Mises Equivalent Stress for Lift-Off/Airloads CaseVon Mises Equivalent Stress for Lift-Off/Airloads Case
lat9ol7lat9ol6
GLAST LAT Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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Radiator Mount Bracket AnalysisRadiator 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
CASE X [N] Y [N] Z [N]
+X/-Z 994 0 -1670-X/-Z -994 0 -1670+Y/-Z 0 333 -1670-Y/-Z 0 -333 -1670LIFT 0 0 32400
GLAST LAT Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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Finite Element Model:Finite Element Model:Parameters and AssumptionsParameters 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/m3 (0.10 lb/in3)
• Yield Stress = 241 MPa (35 ksi)
• Shear Ultimate = 145 MPa (21 ksi)
• Bearing Yield = 345 MPa (50 ksi, 1.5 e/d)
GLAST LAT Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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Results – Stress Contours: Results – Stress Contours: Case +X / -Z LoadCase +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 Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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Results – Stress Contours:Results – Stress Contours:Case -X / -Z LoadCase -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 Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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Results – Stress Contours:Results – Stress Contours:Case +Y / -Z LoadCase +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 Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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Results – Stress Contours:Results – Stress Contours:Case -Y / -Z LoadCase -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 Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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Results – Stress Contours:Results – Stress Contours:Case +Z Lift LoadCase +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
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Results – Loads and Stresses Results – Loads and Stresses at bolt locationsat bolt locations
FS= 1.0
HOLE# +X/-Z -X/-Z +Y/-Z -Y/-Z LIFT MAX Tension Bearing Tear out[N] [N] [N] [N] [N] [N] [MPa] [MPa] [MPa]
11 1877 1659 36 254 3407 3407 9 10 912 169 316 49 102 6868 6868 NA 39 37
13 71 22 31 22 3799 3799 NA 22 2114 449 2202 885 876 13740 13740 NA 78 6115 125 356 116 116 2099 2099 NA 12 916 18 67 22 27 876 876 3 5 522 752 761 858 654 1112 1112 NA 33 3123 187 276 262 196 912 912 NA 27 2624 89 111 116 85 925 925 NA 27 2625 596 227 178 200 7984 7984 24 57 4826 0 0 0 0 16200 16200 48 80 9627 0 0 0 0 16200 16200 48 80 96
LOAD CASE
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Summary of Margins of SafetySummary of Margins of Safety
22
24
23
11
13
1225
14
26
TensionFailure
BearingFailure
Tear OutFailure
FS= +X/-Z -X/-Z +Y/-Z -Y/-Z LIFT Allowable2.0 [Mpa] [Mpa] [Mpa] [Mpa] [Mpa] [Mpa]
Nom Stress 8 9 4 3 94 241Peak Stress 17 18 9 7 189Margin 13.2 12.4 27.2 35.6 0.3
Max Von Mises Stresses
15
16
27
Attach against against againstPoint Tension Bearing Tearout
11 32.4 16.8 6.812 NA 7.9 2.913 NA 15.0 6.014 NA 3.4 1.415 NA 28.0 14.616 119.0 68.4 27.122 NA 9.5 3.623 NA 11.8 4.624 NA 11.6 4.525 19.2 5.1 2.026 9.1 3.3 0.527 9.1 3.3 0.5
Attachment Point Margins of Safety
GLAST LAT Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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RMB ConclusionsRMB 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 Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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Summary and Further WorkSummary 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 Project DOE/NASA Mechanical Systems Peer Review, March 27, 2003
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End of End of Section 7.1Section 7.1
