A telecon was held on Thursday 8/7 at 4pm EDT to status Tracker issues. A brief summary follows:
(A) The excel file "Verification matrix of loads and stresses for the bottom tray" provided before the meeting, via e-mail from Eric Swensen, was reviewed. It was discovered to be missing the 1.25 qualification factor on the CLA load levels. It was discussed and understood that a static pull test to the levels shown in Table 9 of the LAT Environmental Spec must occur to qualify the Tracker flexures. When the missing factor of 1.25 is included on the loads, previous work by Steve Spencer has shown that in order to qualify the side flexure, the axial load developed in the corner flexure becomes so high that uncomfortable safety margins occur for the corner flexure. Jim Ryan suggested, as passed on by Sharon Seipel, that perhaps the corner flexures could be removed from the test, for purposes of qualifying the side flexures. This requires a pretest analysis for this condition, to show that all hardware in the test would still have a comfortable safety margin. We also need to check the qualification cases for the corner flexure to make sure that no hardware will have low margins. Robert Johnson has directed his team to do this analysis.
1. Eric Swensen is to schedule the analysis to occur as soon as possible. Goal would be to have results by next week's status meeting on 8/14.
(B) A discussion occurred of the damage to static test article 1. The bottom face of the sandwich laminate that the detectors attach to has 9 areas of damage. Eight of the damage areas are a "polishing" which occurred from socket head screws rubbing their heads on the laminate, as they were turned to drive a piece of GSE that presses in the corner flexure shear pins. Each of these damage areas is inboard from the corners of the laminate. At the most interior edge of one of the damage areas, is the 9th area of damage. Here the fiber(s) are actually cracked.
COI has suggested a potential repair for both the "polished areas" and the cracked area. Ben Rodini is to travel to Hytec on 4/18 for meetings on 4/18 in the afternoon (desired) or 4/19. He will view the damaged article and the proposed detailed repair procedure.
2. Swensen to provide Rodini with travel directions/contact information for Hytec by COB 4/8. (Ben on vacation next week).
3. Swensen to complete the detailed repair procedure for Rodini's review by 4/18.
4. Rodini to schedule travel plans and notify SLAC/Hytec by COB 4/8.
(C) A discussion was held regarding the discrepant tower sidewalls. It is known that 2 outer plies, one on each side of the panel, were left out of the layup. However, while accounting for the two missing layers, it appears there is also some type of other problem, as some of the panels were found to be undersize in thickness.
One of the undersize thickness panels, coupons for thermal testing (also undersized in thickness), and one panel of the right thickness (accounting for missing plies) are being shipped to SLAC. These will be overnighted to COI for testing. We do not know if the panels were cut from the same laminate or from separate laminates. Rodini suggested that a serialization of all laminates occur for traceability. Rodini has requested the following for each panel to be tested:
-fiber volume test
-photomicrograph (of x-section)
- CMM measurements over test samples to assess uniformity of thickness
- information on the prepreg used to make them (fiber areal weight w/tolerance, resin content w/tolerance)
Once Plyform knew of the thickness issue, they performed some testing of a laminate made specially for this purpose. It contained 22 layers of the K13D material in a uni-directional layup. It showed 86 micron thickness per layer, which is somewhat less than the 98-102 microns expected (per COI). Coupons for a tensile test were cut from the laminate. The average strength was found to be 1200 MPa, which is less than the 1700 MPa expected. Earlier in the week, a similar laminate of 30 layers of K13D uni-directional was fabricated, and the fiber volume tested. It was found to be 59% per Robert Johnson.
Plyform begins a two week shutdown on 8/11. We can not begin to resolve the laminate issues until they return on 8/25. This will cause the final drawing corrections to be put on hold until this matter is closed. Without the corrected drawings, we can not authorize COI to process the fiber into prepreg that Plyform will need to fabricate the new EM Sidewalls. Tom Borden stated that COI has already ordered some of the raw materials it needs from Japan, but further processing will not occur without authorization from SLAC to proceed.
5. Borden to follow-up on shipping of panels to SLAC next week, and overnighting test articles to COI when received.
6. Borden to setup PO for COI to perform testing requested by Rodini on panels.
7. Borden to follow-up with COI that order from Japan has occurred.
THE NEXT MEETING IS PLANNED FOR THURSDAY, AUGUST 14TH, AT 4 PM EASTERN DAYLIGHT TIME. JIM MARTIN WILL GET TELECON PHONE NUMBER AND E-MAIL IT OUT TO EVERYONE.
Please send any corrections/comments on these minutes to me via reply e-mail. (I will be out until 4/12.)