Say, cheese. Food for thought about optical materials properties. Ray Williamson 2016 Ray Williamson Consulting

Transcription

1 Say, cheese Food for thought about optical materials properties Ray Williamson 2016 Ray Williamson Consulting

2 The situation: Optical fabrication is a technological craft. In recent years the tolerances have become more demanding and the master craftspeople have largely retired. The optical shop has evolved from the craftsman s workshop into a series of technicians workstations. A new generation of researchers has advanced the science of material processing. We now have PhD s presenting at conferences on optical manufacturing, and high school graduates lacking even a single course in physics or chemistry attempting earnestly to understand their job tasks. The traditional apprenticeship has disappeared, and a gap has widened between the knowledge base and the production personnel.

3 The challenge: We have a generation of optical techs to educate and train Most candidates lack extensive science backgrounds Yet the subject of optical manufacture has become much more scientific

4 Some concepts they need to understand Young s modulus Poisson s ratio Elasticity Plasticity Ductility Brittleness Chemo-mechanical polishing Toughness Ductile-brittle lapping transition Phase-change behavior

5 What can we do? Make it real! People understand: What they can see with the naked eye What they can hold in two hands What they can watch happen in real time What they can make happen with forces in the range of muscular strength What they have prior and extensive experience with We have excellent physical intuition thanks to extensive life experience

6 To explain arcane concepts, we ll use familiar materials, in convenient, easily manipulable sizes Such as, say

7 Cheese - Or chocolate, Jell-O, spaghetti, rice, ice, etc.

8 Melting point vs. glass transition Ice cubes continue to clink as they melt an abrupt phase change Cold chocolate is brittle Warm chocolate bends Hot chocolate flows This is so good we don t even need a demonstration just recall our experience (Pitch behaves similarly, but wax melts)

9 Team exercise (Discuss) Why do ice cubes crackle when placed in water?

10 Phase transitions boiling rice with a massager

11 Phase transitions freezing rice in a vacuum bag Ductile solid

12 Devitrification Old honey crystallizes. Gentle heating restores it.

13 Young s modulus Parmesan vs. Mozzarella

14 Young s modulus: Parmesan vs. Spaghetti

15 Near-perfect elasticity

16 Elastic limit, ductility Paper clip springs back at small deformation Paper clip takes a set at higher deformation Dry spaghetti springs back at small deformation Dry spaghetti fractures; both pieces remain straight. Piano wire, if available, duplicates shape of spaghetti strand. Vacuum-packed rice makes good demonstration of ductile solid.

17 Ductile-brittle transition in Mozarella

18 Ductile-brittle, cross-section

19 Earthquake! The reason that most earthquake epicenters are between 5 and 15 km deep: The hot, ductile material underneath deforms plastically and does not fracture The brittle material near the surface is under little pressure. In between, brittle material with much weight on top finds itself occasionally ill-supported due to shifts underneath, and suddenly cracks.

20 Brittle scratch formation in as-cast RJ-650 (Red Jell-O )

21 Fused silica, ductile to brittle scratch transition From The Distribution of Subsurface Damage in Fused Silica, SPIE Proc , Miller, Suratwala, et. al.

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23 Brittle fracture in Jell-O Caution! Sharp edges. Note conchoid faces.

24 Poisson s ratio

25 Jell-O vs. cheese Elastic to failure Extreme elongation Practically nonexistent indentations Elastic, brittle Plastic deformation past elastic limit Minimal elongation Prominent indentations Ductile, tough

26 Indentation hardness and fracture toughness vs. grinding rate Rubber, aluminum, and concrete behave differently when impacted: Rubber is highly elastic and returns the energy before reaching its ultimate strength. Aluminum dents, deforming plastically, absorbing thermal energy and reorienting its crystals before fracture. Concrete deforms elastically and fractures, relieving chunks to be swept away.

27 So this illustration uses experience with common materials to counter the persistent notion that softer materials necessarily grind faster.

28 Parmesan: Lapping, grinding, polishing

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31 CONCLUSION This only scratches the surface of accessible analogies. I hope I ve provided some useful suggestions and stimulated some additional thoughts to aid in training efforts. Thank you for your attention!

32 Ray Williamson Consulting