Tutorial Use of Composites in Optical Systems Tutorial Use of Composites in Optical Systems Anoopoma...
Transcript of Tutorial Use of Composites in Optical Systems Tutorial Use of Composites in Optical Systems Anoopoma...
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TutorialUse of Composites in Optical Systems
Anoopoma P. BhowmikIntroduction to Opto-Mechanical EngineeringOPTI 521November 30, 20092
College of Optical Sciences - University of Arizona
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Optomechanical EngineeringOptomechanical EngineeringOPTI 421/521OPTI 421/52111/30/0911/30/09
Overview
IntroductionComposite basicsSome case studiesFailure modesConclusion
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Introduction
Purpose: Provide general familiarity and resources for consideration of composites in optical systemsComplements: A more detailed and thorough paper on the class website
http://www.optics.arizona.edu//optomech/Fall09/...
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Optomechanical EngineeringOptomechanical EngineeringOPTI 421/521OPTI 421/52111/30/0911/30/09
BasicsMain components
Reinforcement material: typically fibers/ particlesMatrix material: typically resin or epoxy
Common forms: pultrusion, laminate, and foam-core
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CalculationsSimple geometry allows for approximation of composite density and Young’s modulus
( )mr
f
f
fm
HWW
+⎥⎥⎦
⎤
⎢⎢⎣
⎡ −+
=
11
1
ρρ
ρ ⎥⎦
⎤⎢⎣
⎡−+=
m
fr
m
ffm A
AnE
AAE
nE 1
Fiberglass-resin example (pultrusion):Fiber specific stiffness = 16 GPa g/cm3
Composite specific stiffness = 68 GPa g/cm3
This is the primary reason we use composites!
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Tailoring mechanical propertiesAlso, additional design degrees of freedom in manufacturing process
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Optomechanical EngineeringOptomechanical EngineeringOPTI 421/521OPTI 421/52111/30/0911/30/09
Case Study: SXA MirrorSXA = 2024 aluminum alloy/ 30% silicon carbide particulate metal matrix compositeChosen over glass and Beryllium
High specific strength, stiffness, stability, moderate machining cost
Beam footprint = 25 cmFinal weight = 806 grams
Fabrication processMachining, thermal stabilization, electrolessnickel plating, polishing, and coating
Final performanceSurface figure was flat to within ~λ/8 power~λ/6 irregularity over any 120mm diameter area
Thermal performance“no change” for exposure to temperatures ~160°C
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Optomechanical EngineeringOptomechanical EngineeringOPTI 421/521OPTI 421/52111/30/0911/30/09
Case Study: Carbon Fiber Mirror
Conical mirror 1.3m diameter, 0.5m height, polished surface area 2m2, total weight 8 kgM46J/EX-1515= ~ 70% high modulus carbon fiber, ~30% cyanate ester resin matrixFor use in ISS experiment: space-qualified materialsThe specific stiffness of CFRP ~ 5 times greater than steel. The coefficient of thermal expansion for CFRP is very low at 1-2 ppm. This is ~ 20 times lower than for aluminum.
Mandrel mold on rotational
mount
Finalmirror
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Optomechanical EngineeringOptomechanical EngineeringOPTI 421/521OPTI 421/52111/30/0911/30/09
Case Study: Cesic MountCesic = carbon-fiber-reinforced silicon carbide compositeVery close CTE to that of silicon foam-core elementVery useful material properties
= Good material for mounting a silicon foam-core element
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Failure Modes Three types: laminar/ plate uniform stress, stress concentration, and sharp cracks
Comparison of laminar failure to isotropic plate failure
Resulting incremental failure
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Failure Modes (2)Failure due to sharp cracks: Use fracture mechanics in same way as for isotropic glassFailure = KI > kIC aYK I πσ=
,20
001, aa
aaFkIC +
=π
2
002, 1 ⎟⎟
⎠
⎞⎜⎜⎝
⎛+
−=da
aaFkIC π
Fracture toughnessgeometry
Stress Intensity Factor
Average stressfailure criterion
Stress concentrationfailure criterion
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Ways to fight failureThermal stability
Proper volumetric balance of high-modulus, reinforcing fiber with negative CTE, and matrix resin with positive CTE
Moisture-induced stabilityFor <1ppm strain change: Use high modulus fiber, low moisture absorbing resin partially pre-saturated with moisture, and have a metal seal with low flaw density (0.1-0.01%), and seal thickness such that the net CTE is 0.00±0.05ppm/°C.
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Comparison of Composite Materials
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Conclusion
There are many design degrees of freedom made available with compositesOver 60 years of US participation in the composite industry: many lessons learnedFurther research
Will drive product cost downWill create new developments
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Some Interesting ReferencesP. R. Yoder, Jr., “Opto-Mechanical Systems Design”,3rd Ed., CRC Press, 2006.“CFRP Mirror” http://www.compositemirrors.com“Athermal telescope” http://www.cesic.de/...html“Cesic Mirror” http://spiedl.aip.org/... “Failure” http://www.emba.uvm.edu/.../me257/M. H. Krim, “Design of highly stable optical support structure” Opt. Eng., 14, 552, 1975 www.optics.arizona.edu/.../Krim%201975.pdf Regarding cost-effectiveness of composites: “Advances in the manufacture of advanced structural composites in aerospace– a mission to the USA”http://www.netcomposites.com/...pdf