Telecon - TKR Bottom Tray Static Test Plan
April 14, 2004
The telecon was attended by SLAC/Hytec and INFN. JK had a presentation ready and sent out via email to all. The presentation addressed the Mech. verification matrix, definition of the load cases and test plan for both the re-qualification of the BT and the workmanship tests of the flight BTs.
Chart 2 should be addressing 18 FM trays and the first tray should be the EM.
JK to send the source of the test matrix that was presented in chart 3.
JK indicated that the CLA was such that the FM/PFM/QM all see the same load levels - minimum required by the GSFC GEVS. JK also explained that the differences here for this case is the number of load cases and not necessarily the load values. This was in response to a comment that proof loading of each tray should be based on the load distribution analysis that JK has to perform. This action is to be completed prior to definition of the final load values in my opinion. The PFM tests (vib) the same as flight and JK confirmed this in his presentation.
Chart 5 was dedicated to the engineering level tests that are going to be completed at SLAC prior and addressed the tests on the cones and the bolt/stud. These tests are to be done using the previous GRID design iteration for schedule purposes. I think some critical design features are being driven by non technical aspects of the program - not in agreement from my POV. There was a question as to the justification if there is an anomaly during these tests - calculated risk was the response.
Chart 6. There were some questions regarding the level of design that has been changed to warrant a complete new Static Qual Test. The list was : closeouts thinned (same as EM), flexure position difference w.r.t the grid and the of course the integration hardware. I think there still has to be a load distribution analysis done before we embark on this test - avoid over test and related problems.
The verification process is still qualitative in my opinion and needs further development. The proc for the integration of the Tower to the Grid and tthe Grid simulator are quite different from that to be used for the static test - chance to play with the integration hardware not proc validation - general agreement on this.
Hytec had a comment that the combined load case will be difficult to achieve with the plan put forward by JK - offline.. I still think we need the load distribution to see what load need to be applied to the bonded joints.
Chart 7. General agreement on the chart!!! - problem with statement of peak load etc - load distribution should be the bible for this level - again.
The discussion was on using the EM BT for the qual tests and then performing the Fm workmanship tests on all the FM trays including the Tower A such that the 2 weeks necessary for the full QM tests (Hytec - 1week???) can be decoupled from Tower schedule - no time in the schedule.
In my opinion time to step back and take a hard look at Tower A schedule declare success with the progress and perform the required minimum set of tests well - PMO issue aside from this issue at hand.
A side discussion on the to be or not to be of the steel bushing in the GRID. AB is convinced it is a bad idea not to put them in. SLAC is being constrained by GRID people. Tough to argue that it is a bad idea - science guys are worried. Lots of reasons for not and no aggressive plan to implement is my opinion.
Note added by Mike Menning:
In my mind the important differences between the static tests previously run at Hytec on the EM tracker and the static tests planned at Pisa on the EM tracker with the redesigned bottom tray are as follows:
1. The loads
2. The fastener location points on the side flexures
3 The eccentric cones, studs, load washers, etc
4. Shims between the flexures and the grid simulator
5. The assembly and integration process for the interface
The importance of differences 4 and 5 should not be overlooked as potential contributors to hardware stresses during the test. Hytec recognized early on that assembly stresses needed to be controlled so that the combination of assembly stresses and the stresses resulting from externally applied loads do not overload the flexures. The tolerance stack up in the previous design permitted an interference condition which would prevent tracker installation in some cases. Accordingly the tolerances have been changed to permit a nominal 0.020 to 0.030 inches clearance between the tracker flexures and the grid. While this clearance level is needed to ensure the trackers fit in the grid bays, the opportunity for overstressing the flexures during installation is significantly increased unless a well defined installation procedure is followed for the planned test.