Tracker Tower 01 Prototype Test & Analysis Overview Erik Swensen June 19, 2002 HPS-102070-0002
Test Background Design Philosophy: Tracker Tower 01 Prototype was used as an engineering evaluation model to reduce risk to the Engineering Model Qualification Test Environment Quasi-Static Limit Loads Liftoff & Transonic: +3.25/-0.8 Thrust & ±4.0 Lateral MECO: Random Vibration 8.7 Grms @ Acceptance 12.3 Grms @ Qualification Test Level in Black Planned Level in Red +6.0 ±0.6 Thrust & ±0.1 Lateral Acceleration Spectral Density (g 2 /Hz) 1 0.1 0.01 0.001 0.0001 Qualification Level Input Spectrum 10 100 1000 10000 Frequency (Hz) Page 2
Test Background (Cont) Analysis Reports available on WWW References in LAT-TD-00793, Summary of Tracker Preengineering-Model Proto-Flight Tray and Tower-Module Testing Mechanical and Thermal Test Results for GLAST Prototype Mid-Trays (HTN-102070-0009-A) Carbon-Carbon Composite Closeout Frame for Space Qualified, Stable, High Thermal Conductivity Detector Support Structures (HTN-102021-0001) DOE SBIR #55197-99-1 DOE Grand #DE-FG 03-99ER82802 Phase I Final Report GLAST Epoxy Thermal Shear Stress (HTN-102050-0023) GLAST Tray Dynamic Response Trend Studies (HTN-102050-0007-A) Page 3
FEM vs RV Test Results Modes Thrust Axis Fundamental Plunge Mode FEM predicted 239 Hz Measured 184 Hz for Qual and 232 Hz for WN Thrust Axis Tray Modes FEM predicted 553 Hz, 585 Hz, 775 Hz, 882 Hz Measured 624 Hz, 632 Hz, 744 Hz, 792 Hz Lateral Axis Modes FEM predicted 89 Hz, 407 Hz Measured 80 Hz-52 Hz (88 Hz WN), 296 Hz-264 Hz (~300 Hz WN) Page 4
FEM vs RV Test Results Damping (Used a Q=15 in FEM) Thrust Axis Tower Q Fundamental mode varied from 18.9 to 2.2 Lateral Axis Q Fundamental mode varied from 17.8 to 3.3 Conclusions Fundamental modes are close to predictions 2 nd lateral mode is off by 100 Hz, recent changes to FEM improved predictions within several Hz The Q varied significantly as the amplitude increased Page 5
Description of Failures in 1st RV Test Thermal Gasket Material Plastic deformation Occurred Caused a relaxation of thermal/pressure contact between bottom tray and grid support, decreasing the fundamental frequency during first RV SideWall Fasteners Loss of Preload Caused damage to sidewall countersink holes Allowed additional movement between bottom tray and rest of tracker tower during first RV Closeout Wall Hairline Fracture Occurred A single fracture was found in one corner after the first RV Initial fracture caused the crack to propagate and resulted in failures in all four corners of the bottom tray during second RV Page 6
Illustration of Fracture from 1 st RV Photo taken after the 2 nd RV Page 7
Tower Finite Element Modeling Detailed FE model was built using simplified tray models; fasteners represented in model for internal load recovery Two base support configurations were studied: fixed base and flexure mount Modal, static (stress & displacement), random vibration and thermal analyses were performed Closeout & Sidewall in Detailed Tower FEM Simplified Tray Models used in Tower FEM Detailed Tower FEM (trays not included) Page 8
Carbon-Carbon Allowables Material Property Testing and Joint Coupon Testing was performed to calculate allowable stresses Allowables were calculated using 80% of the average minimum measured stress from the two tests Tensile Ultimate is 8500 psi Joint Coupon Samples (Failure in Tension) Page 9
Static & Dynamic Stress Analysis Margin of Safety calculated using: Factor of Safety of 1.4 Stress Concentration Factor of 2.1 Computed margins for loads perpendicular to vertical crack length Net section tension failure Maximum Flexure Attachment Fastener Load from Quasi- Static Accelerations Liftoff & Transonic: 120 N (27 lbs) Quasi-Static Margin of Safety: 8.5 Maximum Predicted Load in the Flexure Attachment Fastener from Random Vibration Environment Qualification Level in Lateral (3σ): 1215 N (273 lbs) Random Vibration Margin of Safety: -0.06 Page 10
Possible Cause of Corner Fracture Stress higher than predicted Residual stress in material Assembly stress from non-conforming flexure mount to bottom tray Damping Impact load from unattached sidewall(s) >3s event during random vibration Allowable is lower than predicted Material processing Void content higher than test material Page 11
Load Requirements 3000 Kg Instrument Mass GEVS to 400lbs for specific PSD definition Recommend flowdown of mission specific RV environment reflecting spacecraft and science instrument configuration and mass Page 12
Proposed Action Plan Review design and analysis Evaluate RV environment for mission specific requirements Investigate design modifications Perform analysis to evaluate corner joint to modifications Perform coupon tests of the corner joint with design modifications to evaluate new design Perform RV of the tower using existing hardware with modifications Bottom tray would be replaced Some risk using existing trays since they have been exercised in previous tests (RV and thermal) Page 13
Design Modification Being Considered Reinforce Inside Corner with Bonded Metallic Wrap-Around Doubler Reinforce Inside Corner with Bonded Metallic Doubler * The Flexure may be integrated into the Doubler in either design Page 14
Design Modifications Being Considered Bond & Fasten Flexure to Corner Increase Load Distribution using Larger Insert Heads Page 15
Design Modifications Being Considered Add Material to the far side of the Closeout Wall Add Material to the Bottom of the Tray Remove Pockets used to Lighten the Closeout Mass Page 16
FEM vs Measured Response Comparisons (Backup Slides) Page 17
Tower Vertical Response to RV 10 1 Acceleration Spectral Density Function: Thrust Axis Random Vibration Comparison: Channel 7 (Outside Sidewall) 10-1 Acceleration Spectral Density Function: Thrust Axis White Noise Comparison: Channel 7 (Outside Sidewall) 10 0 10-2 10-1 10-3 Magnitude (g 2 /Hz) 10-2 Magnitude (g 2 /Hz) 10-4 10-3 10-5 10-4 10-5 -12dB Low Amplitude -6dB Launch Levels -3dB Acceptance Levels 0dB Qualification Levels 10 1 10 2 10 3 10 4 Frequency (Hz) Scaled Qualification Level Response 10-6 10-7 Pre -Test Baseline After -12dB Low Amplitude After -6dB Launch Levels After -3dB Acceptance Levels After 0dB Qualification Levels 10 1 10 2 10 3 10 4 Frequency (Hz) Low-Level White Noise Response Page 18
Tower Vertical Response to RV Measured vs Predicted 10 2 Acceleration Spectral Density Function: Thrust Axis Response to Qualification Level Random Vibration: Channel 7 (Outside Sidewall) 10 1 10 0 10-1 Magnitude (g 2 /Hz) 10-2 10-3 10-4 10-5 10-6 10-7 Control Measured Response FEA Prediction White Noise after Qual Test 10 1 10 2 10 3 10 4 Frequency (Hz) Page 19
Tray Vertical Response to RV 10 1 Acceleration Spectral Density Function: Thrust Axis Random Vibration Comparison: Channel 2 (Standard-Convt Tray) 10-1 Acceleration Spectral Density Function: Thrust Axis White Noise Comparison: Channel 2 (Standard-Convt Tray) 10 0 10-2 10-3 Magnitude (g 2 /Hz) 10-1 10-2 Magnitude (g 2 /Hz) 10-4 10-5 10-3 10-4 -12dB Low Amplitude -6dB Launch Levels -3dB Acceptance Levels 0dB Qualification Levels 10 1 10 2 10 3 10 4 Frequency (Hz) Scaled Qualification Level Response 10-6 10-7 Pre -Test Baseline After -12dB Low Amplitude After -6dB Launch Levels After -3dB Acceptance Levels After 0dB Qualification Levels 10 1 10 2 10 3 10 4 Frequency (Hz) Low-Level White Noise Response Page 20
Tray Vertical Response to RV Measured vs Predicted 10 2 Acceleration Spectral Density Function: Thrust Axis Response to Qualification Level Random Vibration: Channel 2 (Standard-Converter Tray) 10 1 10 0 10-1 Magnitude (g 2 /Hz) 10-2 10-3 10-4 10-5 10-6 Control Measured Response FEA Prediction White Noise after Qual Test 10 1 10 2 10 3 10 4 Frequency (Hz) Page 21
Tray Modes Predicted by FEA Tray modes not excited from base excitation Relative Response (scaled value) Tray Relative Response at 519 Hz 1.0 0.5 0.0-0.5 1 4 7 10 13 16 19 Relative Response (scaled value) Tray Relative Response at 666 Hz 1.0 0.5 0.0-0.5-1.0-1.5 1 4 7 10 13 16 19-1.0 Tray Number -2.0 Tray Number Thick-Converter Tray Resonance Standard-Converter Tray Resonance Tray modes excited from base excitation Relative Response (scaled value) Tray Relative Response at 553 Hz 1.5 1.0 0.5 0.0-0.5 1 4 7 10 13 16 19 Relative Response (scaled value) Tray Relative Response at 882 Hz 0.5 0.0-0.5-1.0-1.5 1 4 7 10 13 16 19-1.0 Tray Number -2.0 Tray Number Thick-Converter Trays are Out-of-Phase All Trays are In-Phase Page 22
Tower Lateral Response to RV 10 0 Acceleration Spectral Density Function: Transverse Axis Random Vibration Comparison of the Tower: Channel 2 (Center of +X Sidewall) 10-1 Acceleration Spectral Density Function: Transverse Axis White Nois e Comparison of the Tower: Channel 2 (Center of +X Sidewall) 10-1 10-2 10-2 10-3 Magnitude (g 2 /Hz) 10-3 10-4 Magnitude (g 2 /Hz) 10-4 10-5 10-5 10-6 10-7 -12dB Low Amplitude -6dB Launch Levels -3dB Acceptance Levels 0dB Qualification Levels 10 1 10 2 10 3 10 4 Frequency (Hz) 10-6 10-7 Pre -Test Baseline After -12dB Low Amplitude After -6dB Launch Levels After -3dB Acceptance Levels After 0dB Qualification Levels 10 1 10 2 10 3 10 4 Frequency (Hz) Scaled Qualification Level Response Low-Level White Noise Response Page 23
Tower Lateral Response to RV Measured vs Predicted 10 2 Acceleration Spectral Density Function: Transverse Axis Response to Qualification Level Random Vibration: Channel 3 (+X SW Top Right Corner) 10 1 10 0 10-1 Magnitude (g 2 /Hz) 10-2 10-3 10-4 10-5 10-6 10-7 10-8 Control Measured Response FEA Prediction White Noise after Qual Test 10 1 10 2 10 3 10 4 Frequency (Hz) Page 24