Finite element analysis of DECam May 11 C1 corrector lens – gravity and thermal load cases
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Transcript of Finite element analysis of DECam May 11 C1 corrector lens – gravity and thermal load cases
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6-7 July 2005 1B. C. Bigelow - UM Physics
Finite element analysis of DECam May 11 C1 corrector
lens – gravity and thermal load cases
Bruce C. Bigelow, Physics Department,
University of Michigan 6-7 July 2005
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6-7 July 2005 2B. C. Bigelow - UM Physics
FEA of May 11 C1 element
This talk:
• Conceptual design for an athermal elastomeric lens mount (RTV)
• Description of objectives, model, and load cases
• Deflection and stress results
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6-7 July 2005 3B. C. Bigelow - UM Physics
FEA of May 11 C1 element
Objectives:
• Determine deflections of C1 under gravity loads for RTV mount
• Determine stresses in C1, elastomer, and cell for -20C temp swing
Models:
• 1/2 geometry model
• 3mm RTV elastomeric bond (radial and axial directions)
• Invar cell, FS lens
• Assume a perfectly rigid barrel
Load cases:
• gravity along optical axis
• gravity across optical axis
• steady-state temperature change of -20C
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6-7 July 2005 4B. C. Bigelow - UM Physics
FEA of May 11 C1 element
3d solid (“brick”) elements
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6-7 July 2005 5B. C. Bigelow - UM Physics
FEA of May 11 C1 element
Detail of elastomer bond line
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6-7 July 2005 6B. C. Bigelow - UM Physics
FEA of May 11 C1 element
Symmetry boundary conditions and constraints
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6-7 July 2005 7B. C. Bigelow - UM Physics
FEA of May 11 C1 element
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6-7 July 2005 8B. C. Bigelow - UM Physics
FEA of May 11 C1 element
Gravity across optical axis, deflections across optical axis in meters (2 microns at center)
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6-7 July 2005 9B. C. Bigelow - UM Physics
FEA of May 11 C1 element
Gravity across optical axis, deflections along optical axis, in meters (+/- 2 microns)
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6-7 July 2005 10B. C. Bigelow - UM Physics
FEA of May 11 C1 element
Gravity along optical axis, deflections along optical axis in meters (7.6 microns)
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6-7 July 2005 11B. C. Bigelow - UM Physics
FEA of May 11 C1 element
-20C temp change, max. stresses in Pa (1450 PSI max)
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6-7 July 2005 12B. C. Bigelow - UM Physics
FEA of May 11 C1 element
Stresses in cell in Pa (1450 PSI max)
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6-7 July 2005 13B. C. Bigelow - UM Physics
FEA of May 11 C1 element
Stresses in RTV in Pa (12 PSI max)
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6-7 July 2005 14B. C. Bigelow - UM Physics
FEA of May 11 C1 element
Stresses in lens in Pa (217 PSI)
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6-7 July 2005 15B. C. Bigelow - UM Physics
FEA of May 11 C1 element
Conclusions:
• Gravity deflections seen here are probably negligible
• Thermal stresses are very low relative to yield for all three materials
• The RTV mount provides stiff yet thermally compensating support
• This FEA model is readily adapted to other geometry and materials
• Although 90mm central thickness of C1 appears to be OK for mounting and thermal loads, it will very difficult to fabricate and test. The RTV mount can easily accommodate a thicker lens.