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

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

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

6-7 July 2005 4B. C. Bigelow - UM Physics

FEA of May 11 C1 element

3d solid (“brick”) elements

6-7 July 2005 5B. C. Bigelow - UM Physics

FEA of May 11 C1 element

Detail of elastomer bond line

6-7 July 2005 6B. C. Bigelow - UM Physics

FEA of May 11 C1 element

Symmetry boundary conditions and constraints

6-7 July 2005 7B. C. Bigelow - UM Physics

FEA of May 11 C1 element

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)

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)

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)

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)

6-7 July 2005 12B. C. Bigelow - UM Physics

FEA of May 11 C1 element

Stresses in cell in Pa (1450 PSI max)

6-7 July 2005 13B. C. Bigelow - UM Physics

FEA of May 11 C1 element

Stresses in RTV in Pa (12 PSI max)

6-7 July 2005 14B. C. Bigelow - UM Physics

FEA of May 11 C1 element

Stresses in lens in Pa (217 PSI)

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.