Sag of ZTF components Callahan 9/4/2014. Corrector Trim Plate analysis.
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Transcript of Sag of ZTF components Callahan 9/4/2014. Corrector Trim Plate analysis.
![Page 1: Sag of ZTF components Callahan 9/4/2014. Corrector Trim Plate analysis.](https://reader035.fdocuments.us/reader035/viewer/2022062720/56649f045503460f94c18e07/html5/thumbnails/1.jpg)
Sag of ZTF components
Callahan9/4/2014
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Corrector Trim Plate analysis
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Analytic solution using plate model from Roark and Young predicts 1g deflections of 468 microns.
See MathCad model: sag of corrector.
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FEA assumptions
• Float glass• Thickness 3/8” [9.525mm]• 1 g vertical (Z-axis) loads
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FEA validation. See: sag of correctorFine mesh model: 458 microns
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Loads
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Mesh density: Fine
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Window sag assumptions
• Fused Silica• Outer radius 4406mm• Inner radius flat• Max thickness in center 28mm
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Fracture mechanics models determine the factor of safety for any given stress and probability if success.
• See MathCad model: Design Strength- Fused silica by Callahan
• At 99% survival probability the maximum yield strength is 36 MPa. The Factor of Safety, FOS, can now be calculated for any given applied stress.
• The current stress in the ZTF window at 1 atm (14.7psi) is 10.5 MPa with a FOS=3.4
• At an over-pressure of 1.25 x 14.7psi the FOS decreases to 2.7.
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Z-deflection max 209 microns
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Mesh density
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Loads
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What is the contribution of gravity loading (opposite direction to the pressure load)
Very small ~1.2 microns
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Calculate the sag of the focal plane under 1g
• Assume CCD’s weigh 174 gm each x 27• Force 27.3 N• 1g Z-axis
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Analyze final window design
• Fused Silica• Supported on Delrin “cushions”• Apply various pressures (1 atm)
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Mesh
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Max principal stress
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Add line pressure at O-ring center.
• See Parker O-ring handbook to determine the line pressure. I used a typical mid-value of 2 lbs/in.
• See: https://www.parker.com/literature/ORD%205700%20Parker_O-Ring_Handbook.pdf
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Loads
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Add 2 lb/in line pressure at O-ring center
• Max principal stress increased to 12 psi.
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Substitute Delrin support at the outer location.
• Stress decreases to 6.0 Mpa!!!• Use rough contact between outer delrin and
window to allow separation.
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Max principal 6.0MPa!Lowest stress yet… very uniform.
May be artifically low due to bonded contracts at cushions.
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Deflection under 1 atm~100 microns
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Update model3mm thick delrin Gasket model (1/4 model)
8.9MPa Max Principal stressAt 99% probability of survival fused silica has a maximum strength of 36MPa.
Ths means we have a Factor of safety of 4.0.
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Change gasket to steel to simulate equal support does not change the stress significantly. Max ~8.91 MPa
Stress due to ends separating from gasket are still high.
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To determine the effect of the separeation of the window from the gasket at the corners I fixed the vertical displacement (Z) of the corner.
Stress only reduced to 8.3 Mpa.
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Reduce gasket to uniform 0.24” width.Use Delrin. Stress increases to 9.7MPa
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Change gasket to steel to see how stiffening effects stress. No change
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Increase gasket width to 13.4mm (previously 6.1mm) reduces stress to 8.7MPa
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Sag Absolute7.3 microns
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Sag under 1g plus weight of CCD package (174gm)
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New cable clearance hole size