SUBMILLIMETER ARRAY PROJECT TECHNICAL MEMO 159

Transcription

1 SUBMILLIMETER ARRAY PROJECT TECHNICAL MEMO 159 TITLE: ANALYSIS OF TESTS CONDUCTED ON BUS TUBES FROM ANTENNA 3 TEST DATE: JUNE 21, 21 TEST LOCATION: SIMPSON GUMPERTZ AND HEGER, INC () 41 SEYON STREET BUILDING 1, SUITE 5 WALTHAM, MA TEST PROCEDURE: PROCEDURE NUMBER: , REV. OB TEST ENGINEER: BRENDON WILEY ENGINEER: GEORGE NYSTROM 1

2 INTRODUCTION: The -BUS structure was designed and analyzed by Phillip Raffin while employed at SAO. William Davis (SAO) performed subsequent analyses to evaluate dynamic load inputs caused by Azimuth and Elevation accelerations. The Davis analyses were to ensure the dynamic loads were less than those specified by Raffin for each tube type. These analyses are available in technical memos TM 137, TM 13, TM 119, TM 55 and TM 51. Nytex Corporation manufactured the -BUS tubes in Taiwan to specification number: Nytex performed acceptance testing to the load values given in the specification, which are identical to those employed in our testing program. The project initiated a test program in March 22 in partnership with to provide testing of tubes from our spare inventory and in service Antennas. This testing was reported in Technical memo TM 145. A second test was performed and reported in TM 157 with analysis of test data given in TM158. This test is using Antenna 3 tubes and equivalent type spare tubes. The removed Antenna tubes give us a true test article because of their exposure to the Summit environmental conditions. This allows us to better understand tube health and by implication BUS health. Although this is only a small statistical sample, it may provide an early warning should either the removed Antenna or spare tubes fail. ANTENNA 3 TEST RESULTS: All Antenna 3 tubes and similar tubes from inventory passed the load testing conducted using test procedure Figure, 1 shows a crack that traversed the bond area on Spare tube This is the first tube to have such a failure. It appears to have not lessened the tube s strength. However, this tube must stay in the testing program to monitor this condition. Our belief was that the bond s hoop strength would prevent such a crack from traversing the bond area. 2

3 Figure 1 Crack on tube S8-12 The test program is concerned mainly with pass/fail load testing. We tested the tubes at its maximum expected working load and 1.5 times that load, which is its acceptance test load. However, we also wanted to evaluate the tube assembly s design properties to see if the calculated extension matched the machines corrected measured extension. has noted that the MTS testing machine was not instrumented for making direct tube extension measurements. However, believed that the data could be used to make a reasonable estimate and therefore a better understanding of the tube assembly s design properties. The testing machine is a MTS model 3-G Electro-Mechanical Universal Tester. It measures the crosshead motion relative to its base for a calibrated applied load. The motion is measured in microns and the applied load in pounds force at a 2 hertz sampling rate. The test setup for MTS machines control test is shown in Figure 2 below. A Machine control test was performed to check its operational parameters (software) and proof test the holding fixtures against possible breakage under load. We then performed a calibration test for each tube type. The calibration loads were identical to the tube s test loads. The expected test sample extension is calculable with reasonable accuracy. Therefore, by subtracting it from the total measured extension, one yields the machine s extension. The Machine s error expressed as a percentage is equal to the total measured extension divided by machine extension times 1. 3

4 Machine Control Test setup Figure 2 The Machine calibration data is shown below for the three tube types. Examination of the results clearly indicates that the MTS machine is a large fraction of the measured extension. This is reasonable, since the machine is a traveling bridge type design. Also, comparing the common 84 pound test load for the types 12 and16 tubes indicates measurement repeatability of a few percent. Data from Machine Calibration test for -5 tube type (LBS) TOTAL (µ) CALCULATE ROD (µ) MACHINE (µ) MACHINE ERROR (%)

5 (Lbs) (Lbs) Data from Machine Calibration test for -12 tube type (LBS) TOTAL (µ) ROD (µ) MACHINE (µ) MACHINE ERROR (%) Data from Machine Calibration test for -16 tube type (LBS) TOTAL (µ) ROD (µ) MACHINE (µ) MACHINE ERROR (%) The graphs shown in figures 3-8 below are generated by correcting measurements for the machine error. The Antenna 3 tubes are on the left side with the corresponding spare tube on the right. A3-5 TUBE TEST TUBE TEST S (LBS) Load ( Lbs) Figure 3 Figure 4 5

6 (Lbs) (Lbs) load (lbs) (Lbs) (MICRONS) A3-12 TUBE TEST S-8-12 TUBE TEST (lbs) Figure 5 Figure TUBE A3-16 TEST (LBS) TUBE S CONCLUSIONS: Figure 7 Figure 8 All tubes passed testing, without failure, at their specified acceptance test loads. This is the primary testing purpose and indicates that there has been no measureable deterioration of Antenna tube strength. The calculated stiffness matches reasonably well for the Antenna tubes with a larger dispersion for the Spares. The reason for this is not obvious but most likely relates to how they have been handled and stored. We expect the tubes to fail at their bonded joints. If stored in excessive heat or moisture, then the bonds could be subject to loss of strength. The graphs show larger extension for the three spare tubes. This could well be the case for our spare tubes, since no attempt has been made to keep them stored in a Summit like environment or controlled manner. 6

7 The good correlation of calculated and measured extension versus load for the Antenna tubes verifies the design properties and need not be continued in future testing. We can revert back to just pass/fail testing at their maximum working and acceptance loads. This analysis does imply that the nominal tube manufacturing specifications have been achieved and is sufficient for our understanding the tube properties. How the tubes deteriorate in the future is adequately monitored by testing both Antenna and spare tubes on a month period. If Antenna tubes failures occur, then the test period should be reduced to 6-12 months. If all samples fail, then a meeting must be conducted to determine a course of action. The removed Antenna tubes must be recorded as to their position in the BUS. This will allow determination if tube removal results in Reflector holographic changes. The positions are shown below in the marked up -BUS drawing for Antenna 3 removals. 7

8 8

9 End of Report 9