Material properties

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Material properties
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Overview

• Purpose to give a feel for some common
  materials used in opto-mechanics
• Density
• Structural
• Hardness
• Thermal
• Also to introduce some useful instruments
• Precision balance
• Two ball spherometer
• Thermocouples
• Instron hardness tester

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Density

• Measure volume of samples
• How accurately relative to how well mass is
  measured?
• Measure mass
• Use precision balance
• First zero balance
• Set sample on carefully
• Remove with same care
• What volume corresponds to the smallest mass
  measureable?
• Will contamination effect your measurement?

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Structural properties

• We are not well set up for this instrument was
  late
• Support sample across two rolls
• Place strap around middle, connect to scale
• Place two ball spherometer on top of sample
• Why use this method of measuring deflection?
• Jack up table to load sample
• Record deflection versus load
• Calculate Youngs modulus

5
Thermal properties

• Coefficient of thermal expansion
• Approximate but can see relative differences
• Thermal conductivity
• Change T by known amount and plot ?T at end
• Do answers relate to how warm material feels?
• Heat capacity
• How much does heat source cool as sample warms

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Hardness

• Have new hardness tester
• Uses 1/16 carbide ball
• Forces ball into material being tested
• Measures depth of penetration d at certain force
  f
• Hardness is df with various scaling factors
• Get instruction before using machine
• Make sure sample is clean, both sides
• Fits anvil well
• Contamination will affect answer

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Spring Wires

• Idea - familiarity with the flexibility of
  different materials
• Also idea of permanent deformation
• Flex to failure
• With shape memory wire see how it behaves
• Use heat gun
• In vibration lab well look at torsion of wires

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IR Optical Materials

• Calcium fluoride - transparent in visible
• Thermally sensitive, brittle, softer than most
  glasses
• Silicon opaque in visible xparent 2-5 µm
• Index about 3.0 so what is its reflectivity
• Germanium opaque in visible, xparent at 10 µm
• Index about 3.5
• Sapphire Al2O3 very hard, low CTE
• ZnSe yellowish, some visible transmission, soft
• Moderate index, reasonably tough

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Examples of good O-M practice

• Adhesive mirror mounting
• Kinematic mounting and adjustment
• Flexure features including flex pivots
• Low stress adjustments