Or how to avoid breakage, berylliosis and/or...
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Transcript of Or how to avoid breakage, berylliosis and/or...
Overview
Important material propertiesDesign-centered EnvironmentalFabrication
Material classes and common examplesMetalsPolymersCeramicsComposites
Material Properties - Overview
Design-Centered PropertiesSatisfy functional requirements
Environmental PropertiesConstraints based on operating environment of apparatus
Fabrication PropertiesConstraints based on cost, available processes, and manufacturing quantity
Material Properties - Overview
ResourcesMatWeb (www.matweb.com)Machinery’s HandbookChemical Resistance Database (http://www.coleparmer.com/TechInfo/ChemComp.asp)McMaster-Carr (www.mcmaster.com)
Material Properties - Design
Mechanical PropertiesYoung’s modulus, density, fracture toughness
Electromagnetic PropertiesDielectric strength, transparency, permeability
Thermal PropertiesThermal conductivity, heat capacity
Material Properties – DesignMechanical Properties
Failure is not as simple as yield stress!Yield stress
Processing sensitive, maybe anisotropicCreep
Stay below 1/3 of melting point (in K)Fatigue
Some materials fatigue even at low stressFracture
Very common failure mode, but very complex
Material Properties – DesignMechanical Properties
Watch for tempers, fillers, and/or temperatures used for mechanical property measurementsBrittleness indicators
Low elongation (< ~10%)UTS close to yield stressVery different notched/unnotched impact energy (Izod or Charpy tests)
Material Properties – DesignElectromagnetic Properties
Dielectric StrengthWatch out for short circuits!
Transparency / ColorThere are very few clear materials
Electrical ConductivityMagnetic Permeability / Hysteresis
Special alloys with tailored properties are available
Material Properties – DesignThermal Properties
Thermal ConductivityGood insulators are not strong materials
Thermal Diffusivity
Material Properties – Environment
Operating temperature rangeRemember to watch the low end, too!
Chemical resistanceIf in doubt, buy a material sample and test itCleaners matter too!
Radiation resistanceIncludes solar UV radiation!
AppearanceDoes it need to be shiny and impressive?
Material Properties - Fabrication
You are making one machine, not 106
Casting, molding, forging, and stamping are not economicalBenefits of rapid prototyping may offset poor material properties
Machinability directly impacts costHazardous materials more expensive to work
DON’T TRY THESE YOURSELF!Beryllium, magnesium, glass-reinforced plastics, etc.
Materials - Metals
Aluminum PropertiesHigh strength/weight ratioNo fatigue limit (vibration = trouble!)Widely variable toughnessMost alloys resistant to air, humidity, solvents
Acids and bases very bad!Inexpensive and easy to work
Materials - Metals
Aluminum AlloysMachining
6061, 2024, 7075Forming
5052, 3003, 6063Welding
6061, 5052
Materials - Metals
Carbon and Alloy Steel PropertiesHeat treatment allows even a single alloy to have widely variable propertiesIn general, toughness and yield strength inversely proportionalWell-defined fatigue limitPoor corrosion resistanceInexpensive, but can be hard to machineWeldable
Materials - Metals
Steel Alloys1018: General purpose, low strength4140: Higher strength, heat treatableTool Steels
Many proprietary varieties availableDifficult to machine or formS7 good for high-impact structural applications
Maraging SteelsUltra-high strength and toughness, but very expensive
Materials - Metals
Stainless Steel PropertiesWide range of corrosion resistance
Some little better than alloy steel!Difficult to machineModerate costMost corrosion-resistant alloys not strong
Good at low temperaturesCan be easy to weld
Materials - Metals
Stainless Steel Alloys304: Most common, resistant to common conditions316: Extreme corrosion resistance, very difficult to machine, low strength440C: High strength, relatively low corrosion resistance
Materials - Metals
Copper Alloy PropertiesHigh thermal and electrical conductivityWidely variable strength and machinabilityModerate costCorrosion resistant, but can tarnishEasy to join by brazing/soldering
Materials - Metals
Copper AlloysBrass
Alloy 360 is strong and extremely machinableBronze
Alloy 630 is very hard and wear-resistantBeryllium Copper
Superb properties, but VERY TOXICFew shops will work it, and only for big $$$
Materials - Metals
MagnesiumLightest structural metalFlammable during machiningTarnishes and corrodes easily
TitaniumVery high strength/weight ratioMore corrosion resistant than stainless steelVery difficult to machine or form
Materials - Plastics
AcrylicTransparent and UV resistantStiff and strongVery brittleEasily solvent-weldedEasily laser cutDifficult to drill or machine
Materials - Plastics
PolycarbonateTransparent, but not UV resistantImpact resistant, but notch-sensitiveEasy to machine
Materials - Plastics
DelrinVery easy to machineSomewhat brittleLow friction
TeflonVery easy to machineVery solvent resistantExpensive
Materials - Ceramics
Not machinable without special equipment/experience
Even “machinable” ceramics aren’tHigh strength with high dielectric strengthHigh temperature capabilityVery brittleVery expensive