1. 6-7 July 20051B. 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

2. 6-7 July 20052B. 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

3. 6-7 July 20053B. 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

4. 6-7 July 20054B. C. Bigelow - UM Physics FEA of May 11 C1 element 3d solid (“brick”) elements

5. 6-7 July 20055B. C. Bigelow - UM Physics FEA of May 11 C1 element Detail of elastomer bond line

6. 6-7 July 20056B. C. Bigelow - UM Physics FEA of May 11 C1 element Symmetry boundary conditions and constraints

7. 6-7 July 20057B. C. Bigelow - UM Physics FEA of May 11 C1 element

8. 6-7 July 20058B. C. Bigelow - UM Physics FEA of May 11 C1 element Gravity across optical axis, deflections across optical axis in meters (2 microns at center)

9. 6-7 July 20059B. C. Bigelow - UM Physics FEA of May 11 C1 element Gravity across optical axis, deflections along optical axis, in meters (+/- 2 microns)

10. 6-7 July 200510B. C. Bigelow - UM Physics FEA of May 11 C1 element Gravity along optical axis, deflections along optical axis in meters (7.6 microns)

11. 6-7 July 200511B. C. Bigelow - UM Physics FEA of May 11 C1 element -20C temp change, max. stresses in Pa (1450 PSI max)

12. 6-7 July 200512B. C. Bigelow - UM Physics FEA of May 11 C1 element Stresses in cell in Pa (1450 PSI max)

13. 6-7 July 200513B. C. Bigelow - UM Physics FEA of May 11 C1 element Stresses in RTV in Pa (12 PSI max)

14. 6-7 July 200514B. C. Bigelow - UM Physics FEA of May 11 C1 element Stresses in lens in Pa (217 PSI)

15. 6-7 July 200515B. 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.