MINUTES From 8 July Meeting:
A. Review of previous action items:
ART-1: Provide ART with test result data from Vibration Tests (LAT-TD-00788) - Horn Closed
ART-2: Provide ART results of insert pull out tests - Johnson - Open
Current Status: Tom Borden to work with Hytec to provide data
ART-3: Provide ART the properties for the carbon-carbon material - Johnson - Closed
ART-4: Provide a recommendation for design practice and analysis cases for redundant load path considerations - Rodini - Closed
- Ben Rodini pointed out that the 8.5KSI Carbon-Carbon tensile strength seemed low relative to other structural applications.
- Ben Rodini reviewed concerns with tolerance variance impacting load path design limits with inserts. A conservative approach would be to assume half the inserts were load bearing . Discussion with the tracker team indicated that insert location was controlled to within 2mils on both sidewalls and base. Ben indicated that this level of tolerance control was good and would allow the use of something like 1.25 (TBR) load factor to account for tolerance uncertainty.
- The ART recommended that the locking feature for the system be selected & incorporated into the design prior to the next test
- The flexure design was discussed and concern expressed as to the FEM complexity impact of multiple piece flexures vs. single piece. The primary concern being whether we understood the flexure contribution to total load at the corner interface. The tracker team indicated that design trades required multiple piece approach due to space limitation. Hytec also indicated that although more complex their FEM correlated well with observed flexure behavior. The ART indicated that the tracker team design load should also consider uncertainty due to flexure design complexity. Ossie Millican indicated that he may be able to conduct some special tests with spare flexures if it would help understand this uncertainty.
- The gasket approach and impact on dynamic response was questioned by Minh Phan. He pointed out that frequency instability results from the tests would not allow model correlation or ensure dynamic response loads to be known. The move towards a non polymeric thermal gasket should reduce this issue. It is clear that additional dynamic analysis will be required to assess proposed corrective actions.
- Tsune Kamae indicated that a worst case design load condition should consider the impact of the grid distortion and resulting off-set of tower to grid interface. The condition may adversely impact the direct load path through the corner flexures.
- The ART believes that there are sufficient factors that could contribute to a greater than expected load at the corners to cause failure. An analysis of these factors was proposed by Tom Borden to assess strength requirements. It is anticipated that this analysis will show sufficient plausible failure modes to provide a basis for corrective action.
- The ART is also concerned that the design environment may be overly conservative for this application and it may be reasonable to reduce the environment to some extent by accounting for attenuation through the structure. Ben Rodini indicated that Swales is looking into this. Ben and Bernie Graf to coordinate this effort with the project office.
- Dick Horn requested that ART members provide an email to him summarizing their view of findings to date
C. New actions:
ART-5: Distribute a proposed analysis plan to the team and review it at the next ART - Borden - ECD 9 July
ART-6: Coordinate a review of environment requirements - Graf/Rodini - ECD 15 July
ART-7: Consider & recommend plan for additional flexure testing - Borden/Millican - ECD 9 July
Please provide any corrections/clarifications of these minutes to Dick Horn prior to the next meeting 9 July