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TART recommendations implementation and qualification program results Alessandro Brez INFN - Pisa

Gamma-ray Large Area Space Telescope. TART recommendations implementation and qualification program results Alessandro Brez INFN - Pisa Brez@pi.infn.it. Agenda. Summary of the TART recommendations and their implementation Peel test results Test articles description

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TART recommendations implementation and qualification program results Alessandro Brez INFN - Pisa

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  1. Gamma-ray Large Area Space Telescope TART recommendations implementation and qualification program results Alessandro Brez INFN - Pisa Brez@pi.infn.it

  2. Agenda Summary of the TART recommendations and their implementation Peel test results Test articles description Thermo-vacuum test results Conclusions

  3. TART recommendation 1 Qualification program • The qualification program has addressed the recommendations of the TART: • Main activities: • Tests and analysis of the materials and their compatibility to 3M2216 • Revision of the assembly procedures and of the assembly environment • Construction of 3 tests articles to test different solutions implementing the new procedures in a improved environment • Thermo-vacuum tests of the test articles

  4. TART recommendation 2 Tungsten surface preparation Recommendation: Etch the tiles surfaces by MIL-HDBK-961B process (degrease + acid bath) and prime with BR-127 Test the results with peel tests Actions: 2 processes have been investigated: GSFC adopted MIL-HDBK-961B and primed the tiles with BR-127 Vaiarelli (Venaria, Turin) Company process + Plyform BR-127 priming

  5. Tungsten preparation: GSFC results

  6. Included Material Stringers Figure 3. Cross section of tungsten foil showing “stringers” of included material.~ 200X Figure 5. SEM photograph of included material. EDS revealed very high carbon, low tungsten content in included material as opposed to tungsten base material Tungsten preparation: GSFC analysis of W tilesAnalysis Performed by: Debbie Thomas, Code 541/ Swales, 301-286-8577

  7. Figure 6. The photograph on the left was taken on the metallograph (~ 200X) and the one on the right was taken on the SEM. Both show an unusual expansion of the base material (compare the photo on the left to the one in Figure 3 taken at the same magnification). Tungsten preparation: GSFC analysis of W tiles No clear conclusions. The 120oC bakeout did not reveal extrusion of material from the W tiles. Delamination of the W tiles themselves never observed The anomalies can be related with the synterization process used for W tiles The thick W tiles are from a W alloy (kulite alloy K1750) to have smooth and machinable tiles

  8. Peel test of sand blasted tiles First action: W sand blasting : controlled and uniform roughness of the tiles Qualification test: peel test 1N/mm~6lb/inch F The debonding pattern at 1mm roughness was better: At Ra=0.5mm film left on Kapton At Ra=1.0mm film left part on Kapton and part on W Tray MID 48 assembled with sand blasted tiles gave acceptable results

  9. Peel tests of Turin etched tiles The sand blasted coupons were cured at RT in normal atmosphere with a not quantified mechanical pressure. Bond thickness 0.1mm. The Kapton foils were not abraded. The etched coupons were cured at RT in a vacuum bag. Bond thickness ~60mm. The Kapton foils were abraded. 4 tests have been performed with etched and primed tiles Results: in 1 case the adhesive layer was left part on W, part on bias circuit. Peel strength=2.1N/mm, comparable with the sand blasted tiles taking into account the different adhesive thickness. In 3 cases there was a complete failure on the Kapton side with rather low and disperse peel strength values (from 0.2 to 1.4 N/mm) 3 tests have been performed with etched tiles without primer. In 2 cases the failure was on kapton side, peel strength=0.8,0.9N/mm In 1 case some of the adhesive, in the central part of the tile, was left on bias circuit. Observed a non uniform glue thickness. Strange pattern. Peel strength=1.4N/mm Conclusions (qualitative) The adhesion of the 3M2216 to the W tiles was generally good The adhesion of the 3M2216 to the Kapton was often bad need of comparison tests of abraded and unabraded Kapton foils

  10. TART recommendation 3 Bias circuit preparation • Roughen surface with Scotch Brite pads until sheen is removed • Clean (acetone wipe + IPA wipe) • Bake 60oC for 12hours • Clean (acetone wipe + IPA wipe) • Wait 30 min • Bond The process has been implemented in Plyform (INFN_LAT_MECH_008_2) After the ambiguous results of peel the tests 2 sets of peel tests coupons have been prepared with abraded and unabraded kapton foils glued on Al specimens with 3M2216. Peel strenght of unabraded samples = 1.1N/mm 0.5N/mm Peel strenght of abraded samples = 3.5N/mm 0.35N/mm

  11. TART recommendation 4,5 Tungsten bonding The recommendation describes in details the W tile bond process and the preparation of the adhesive with degassing. The recommendations have been implemented INFN_LAT_MECH_009_02 Adhesive preparation INFN_LAT_MECH_006_02 Tungsten and bias circuit bonding

  12. Grounded tile Not grounded tile TART recommendation 6Grounding of Tungsten tiles Test article 2 Planarity 170mm Test article 2 Planarity 224mm A wire sticks out from the tray after gluing MCM front MCM front Aluminum gold plated 55mm wires Test article 2 Planarity 139mm A wire sticks out from the tray after gluing Conclusions: The system does not guarantee the tiles grounding The vacuum extracts the wires to the edge of the tray, very dangerous! The wires seem to compromise the final planarity of the tray MCM front

  13. Do we need W tiles grounding? GFSC primed W tile 0.06mm 3M2216 film (cured 15h at 40oC) Any buildup charge will disappear in few seconds Al base A I V Keythley 467 Breakdown to 1.4KW C=6nF R=~1GW at 1V t~6s

  14. TART recommendation 7,8Process cleanliness, QA control A detailed list of manufacturing rules have been dictated. These rules have been incorporated in INFN-LAT-MECH-007-01 INFN personnel made detailed revision of all the Istruzioni di Lavoro (Work Instructions) and will directly overlook the construction of the first trays. The real main effort to satisfy the request of a clean area insulated from the rest of the Plyform activities, has been the purchase of a clean-tent dedicated to GLAST tray assembly. The tent will be ready to work on October 4th. • Mandatory inspection points have been introduced: • Tile cleanliness and priming with routinely peel results • Kapton preparation • Adhesive preparation and deposition with hardness tests

  15. TART recommendation 9Non use of grid blasted tungsten The 0.1mm sand blasted tiles are no more flat. We cannot use them in any case  segregated TART recommendation 10 Bond joint compression A possible cause of bubbles: The Kapton is hold flat by the tool during adhesive curing. A local depression of the tray surface (50mm or more) could cause a bridge effect steel vacuum chucks Bias circuit tray 3M2216 Proposed solution: Add a compliant pad between tool and bias circuit to compensate the tray irregularities. A suitable material has not found up to now. The test of this solution will be addressed again if needed.

  16. TART recommendation 11Alternate bond cure protocol Cure the 3M2216 adhesive at 35oC in a oven for 18hours • Pro: • Better controlled cure cycle. • The whole cure cycle is under vacuum. • At the beginning the adhesive is more fluid + higher temperature => better outgassing • Contra: • Possible deformation of the tray due to CTE mismatch • 2 test articles have been produced at 35oC

  17. TART recommendation 12Examine bonding integrity of the EM tower Only one tray of the EM tower is representative: The TOP TRAY has the W thin tiles + the final version of the bias circuit, with the continuous Cu layer insulated by a smooth Kapton layer. The TOP EM tray is equipped with dummy ladders After the optical inspection, taping the tray and the ESPI test, we hadNO evidence of defects 726Hz, first tray resonance mode 1251Hz, Second tray resonance mode 2443Hz, first ladder resonance mode

  18. Test articles Thermo-vacuum cycles (P<10-2mBar, min P=50mbar)

  19. Top faces behavior Very good results of bias circuit adhesion on face sheet up to 75oC

  20. Bottom face #3 NO primer 60oC development of a Ø25mm delamination 65oC debonding over 3 whole tiles 70oC one more tile debonded Perfect clean W tile Very good and uniform 3M2216 film on bias circuit Very good adhesion to the previous glue layer (no Frecot55 pollution)

  21. Bottom face #1 primer RT

  22. Bottom face #2 primer 35oC The best result in terms of n. of little bubbles and temperature stability

  23. TART qualification program indications The best results have been obtained with the configuration These options + the specific procedures to match the TART recommendations are included in the LAT-DS-01584 procedure

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