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Materials Selection Questions with
Correct Answers
K vs. KIC - ANSWERS(2γsE)1/2= σ(Πc)1/ K (stress intensity factor- geometric loading) = KIC (Fracture Toughness- material parameters) G=2γs (brittle) G= 2(γs+γp) (ductile materials) K> Kc → Fracture Primary Shaping - ANSWERSCasting- sand, die, investment Moulding- injection, compression, blow Deformation- rolling, forging, drawing Powder- sintering, HIPing, slip casting Composite Forming- hand lay up, filament winding, RTM Special Methods - Rapid Prototype, lay-up, electroform Properties and Examples
- General
- Mechanical
- Electrical
- Magnetic
- Optical
- Chemical - ANSWERSgeneral- cost, density Mech- strength, stiffness, toughness Therm- conductivity, diffusivity, heat capacity, expansion Electr- dielectric constant, conductivity Mag- remanence, saturation magnetization
Opt- refraction, absorption Chem- corrosion resistance Mechanical Properties - ANSWERSE- Elastic Modulus σy- yield strength KIC- fracture toughness ρ- density Thermal Properties - ANSWERSTmax- limiting Temp Cp- heat capacity λ- conductivity diffusivity α λ/Cp Chemical Properties - ANSWERSintrinsic resistance of a material in a given environment 1(Very good) - 5(bad) What happens to solids when we put forces on it? - ANSWERS1) Deformation- shape and volume
- internal structure changes polymer chains, lattice structure, etc.
- fracture What is Hookes Law? - ANSWERSIt applies to linear elastic materials and relates stress of a body with strain in the elastic regime σ= Eε Yield Stress - ANSWERSwhen a material begins to permanently plastic deform. For metals its hard to determine yield point, so an estalbished rule is 0.2%. Draw parallel line from ε= 0.2% to curve Ultimate Tensile Strength - ANSWERSlargest stress a material can undergo before onset of necking Necking - ANSWERSlocal deformation that produce drop in load. This is the onset of fracture. (nonuniform plastic) Poisson's Ratio - ANSWERSthe amount of transverse contraction when strained in a given direction ν= -εy/εx
Metal Characteristics - ANSWERS-tough - KIC
- stiff- high E
- ductile
- wide range of strengths dependent on composition and processing
- thermally and electrically conductive
- reactive- low corrosion resistance Hybrid Characteristics - ANSWERS- expensive
- difficult to shape and join
- properties dependent on combination of materials What makes up a materials property profile? - ANSWERSDensity, mechanical properties, Therm Prop, elect Prop, Optical prop, corrosion prop and processing characteristics environmental impact typical applications choice of process is based on - ANSWERSmaterial shape dimensions, precision
to be made
Process Families - ANSWERS1) Shaping- primary (creates shape)
- Shaping- Secondary (modifies shape or properties)
- Joining
- Surface Treatment Secondary Processes - ANSWERSMachining- cut turn, plane drill, grind Heat Treat- quench, temper, age- harden Joining - ANSWERSFastening Riveting Welding, Heat Bonding Snap Fits, Friction Bond Adhesives, Cements Surface Treatment - ANSWERSPolishing, Texturing Plating, Metallising
Anodise, Chromising Painting, Printing Effects of processing? (1) What happens to rubbery when voulcanized? (2) What happens when you anneal a metal? (3) Glass and a specific heat treatment? (4) What's the result of electroplating? - ANSWERS(1) Soft stretchy --> hard, brittle (2) increase ductility (3) becomes bullet proof (4) improves corrosion resistance How do atoms pack? What materials pack each way? - ANSWERSamorphous --> glasses long carbon chains --> polymers crystalline --> metals, ceramics Def: Lattice - ANSWERScomposed of infinitely many periodically spaced points such that each point is equivalent -environment around each point is the same Def: unit cell - ANSWERSthe basic repeating unit of the lattice with points at the corners
- can also have internal points Def: crystallographic planes - ANSWERSany set of parallel and equally spaced planes that may be supposed to pass through the centers of atoms in crystals Rules for drawing planes from given Miller Indices - ANSWERS1) Take reciprocal of Miller Indices (write it)
- draw cube and choose origin
- Plot intercepts, trace back to origin every time
- connect intercepts to form plane Rules for Indexing a plane that's drawn for you - ANSWERS1) identify origin
- identify intercepts
- take reciprocal
- normalize (h,k,l) so that h, k,l are integers What does each mean? (h,k,l)
Powder- sintering, HIPing, slip casting Special- rapid prototype, layup, electroform (NO MOULDING, COMPOSITE FORMING) Metals Secondary Processes - ANSWERSALL Machining- cut, turn, plane, drill, grind Heat Treat- quench, temper, age harden Metals Joining - ANSWERSFastening, Riveting Welding, Heat Bonding (NO SNAP FITS, FRICTION BOND, ADHESIVE, CEMENTS) Metals Surface Treat - ANSWERSALL polishing, texturing plating, metallising Anodise, chromising painting, printing Ceramics Crystal Structure What determines? - ANSWERSA-X type AmXp, AmBnXp Ionic (+) metal ions= cations (-) nonmetal ions- anions determined by size and charge neutral rc/ra < coordination # related to radius Ceramics - ANSWERS-thermal/electrical insulators -resistant to high T and harsh environments -hard but brittle -high wear resistance -compression strength Classification of Ceramics - ANSWERS- Traditional- white wares, cement ex. brick, tile, porcelain, clay, abrasives
-Advanced= +electro + Advanced structural or oxides non-oxides- carbides, borides composites- ___ mixtures Ceramics Primary - ANSWERSonly powder methods
- sintering, HIPing, slip casting NO SECONDARY Ceramics Joining - ANSWERSonly adhesives, cements Ceramics Surface Treatment - ANSWERSonly- polishing, texturing Def: Polymers What's the most common one? - ANSWERSlarge long chained molecules Poly- more than 2 mers- Compounds (building blocks) Polyethylene- grocery bags, shampoo bottles, bullet proof vests, toys Atomic Packing in Polymers - ANSWERScovalently bonded C and H form the backbone Energy required to break C-C bond Degree of Polymerization? Controlled by? - ANSWERS# of mers- 2,000-5,
controlled by heat input and catalyst or reagents
Types of Polymers (I) - ANSWERSlinear branched cross-linked Types of Polymers and Examples (II) - ANSWERSThermoplastic- linear and branched Recyclable plastics Thermoset- Cross-linked Epoxy, Eggs
Polymers Surface Treatment - ANSWERSplating, metalising Composites, what is a prepreg? - ANSWERSconsists of a combination of a matrix (or resin) and fibre reinforcement. It is ready to use in the component manufacturing process Available in undirectional form and fabric form Placement methods and details - ANSWERSHand layup- individual prepreg tape placed by hand, high labor cost, low facility cost Tape Laying Machine - multi axis controlled machine places tape, lower cost for flat and single curvature points, can't do high curvature Filament winding- individual fibers dipped in resin and wound into a rotating mandrel, limited to near cylindrical shapes, can wrap hoop or helical plies, used mostly for rocket motor cases, low cost, prepreg not needed Consolidation Methods - ANSWERS1) Vacuum bagging
- Autocalve
- Oven cure
- electron beam/laser cure Voight Model - ANSWERSIso strain (stress and fibers in same direction) E composite= EaVa + EbVb Reuss Model - ANSWERSIso-stress 1/Ecomposite- Va/Ea + Vb/Eb Fiber aspect ratio - ANSWERSfibers are very strong, tensile strength increases with glass fiber length Orientation of fibers - ANSWERStensile strength strongest when fibers are in the same direction as stress Composite Lay-up - ANSWERSlamina- orthotropic properties laminate -isotropic/anisotropic properties determined by composite design -fiber orientation used to specify composite lay-up Performance - ANSWERSFGM Equation
F- Function- P, δ G- Geometric- R, cosθ m- material- E,ρ,σlimit What is strength limited design concerned with? - ANSWERSavoiding plastic deformation or yielding What metal forming operations rely on controlled plasticity? - ANSWERSforging, rolling, deep drawing Relationship of σ and σy - ANSWERSσ< σy --> elastic σ> σy --> onset of plasticity σ> σy --> total plasticity, forming, plastic hinges where does max stress occur? - ANSWERSat surface (>σy in cases 2/3) small zones of plasticity appear where stress is highest *Note- even though plastic zone yielded, it still carries a load (1) Onset of plasticity (2) Full plasticity - ANSWERS(1) There's an "apparent" max stress (2) There is a "failure" moment caused by the constant stress distribution over section MF= Zpσy Zp/ze > Crystal unit structures
- atoms/cell
- a
- packing Factor
- Coordination # - ANSWERSFCC- 4 atoms/cell, a- 4/√2 r, PF- .74, CN- BCC- 2 atoms/cell, a 4/√3 r, PF- .68, CN- Simple- 1 atom/cell, a- 2r, PF-.52, CN- HCP- CN- How do you solve for packing factor - ANSWERS(volume/atom) * # atoms / ( volume unit cell)
During plastic deformation of polymers, necking involves - ANSWERSthe alignment of long carbon chains The elastic behavior of polycrystalline metals and ceramics is ___ isotropic/anisotropic - ANSWERSisotropic- nothing varies due to direction anisotropic- glass wood- along grains is strongest What family of low indices can be found in the (100) plane? - ANSWERS(100) (010) (001) Why is Esteel 1000 times greater than Epolyethylene? - ANSWERSsteel- crystalline structure, ionic bonds, long range order polyethylene- long carbon chains, covalently bonded poly- valQ bond between chains Steel titanium- metallic bonding What would Young's Modulus for the composite be along the directions of the fibers? What if composite transverse, perpendicular to fibers? - ANSWERSE comp (parallel)= VaEa + VbEb 1/ Ecomp (perpendicular) = Va/Ea + Vb/Eb Which class of materials has a good balance of RT properties, is corrosion resistant, is supple, but is brittle at low T's and weak at high T's? Metals/ceramics/polymers - ANSWERSpolymers?? On a potential well the equilibrium distance between atoms is on the order of? - ANSWERS1 nm? True/ False The Young's modulus for Zirconia (ceramic) is about the same as steel but 100 times greater than for nylon - ANSWERSnylon- polymer True? Metal Fatigue
How many cycles define transition from low to high cycle fatigue? - ANSWERSlow < 10, Metals and alloys equal the activation energy for [oxidation|dislocation motion|diffusion]
- ANSWERSdiffusion Density of material is related to ____ - ANSWERSatomic packing efficiency X atomic size X2. molecular weight X35!!! Scientists worked hard to get spherical powders because they ___ - ANSWERS?? Which class is a good thermal and electrical conductor, stiff, relatively dense, has poor oxidation, and corrosion resistance? - ANSWERSMetals Which class can be investment cast to near net shape? - ANSWERSMetals Formation of polymer matrix composites requires what 3 steps? - ANSWERS(1) lay up (2) Heating (3) True|False Amorphous glasses are brittle at room temperature but easily deformed and processed and shaped at elevated temperatures - ANSWERSTrue Will Alumina burn in earth's atmosphere? What about carbon carbon composites? - ANSWERSCeramic- Al2)3 --> NO Carbon-carbon --> YES HIP stands for? - ANSWERShot isostatic pressing used for densification Processing Methods| Used For -tape machine lay-up
- injection molding
- powder, sintering -rolling, forging
- slip casting -investment casting
- autoclave consolidation - ANSWERStape-composites
no dislocation motion! atoms cleave Coffin- Manson Law - ANSWERSlow cycle fatigue Thermal Properties Tg Tmax Tmin λ α - ANSWERSTg- polymers and glasses soften Tmax- to avoid oxidation Tmin- to avoid brittleness λ- steady state flow of heat α- cubic- isotropic, noncubic-anisotropic Creep - ANSWERSslow, continuous deformation with time metals/ceramics: Thigh> 0.5 Tm Polymers: Thigh > Tg Stages of Creep - ANSWERS(1) primary- deformation fast until strain hardens (2) steady state- linear response, strain hardening (recovery) (3) tertiary- necking Design against creep in metals Diffusion Creep Dislocation Creep - ANSWERSDiffusion- low stresses, high T Grain size important, big- good Dislocation- intermediate stress and Temperatures introduce obstacles to dislocations solid solution, precipitates, dispersion use high Tm materials Reduce Creep in Polymeres - ANSWERSincrease cross linking (increase Tg) Crystalline polymers better than glassy
make composites by adding fibers Creep in ceramics How to avoid? - ANSWERSmostly diffusion creep glassy phases (oxides) lead to grain boundary sliding reduce diffusion and dislocation motion reduce/control grain boundary phases Types of Reflection - ANSWERSSpecular- angle in = angle out, smooth surface, irregularities < λ Diffuse- all directions, too rough, irregularities > λ Energy Compromise - ANSWERScancelation of external field while retaining magnetization of the material --> form magnetic domains Radiation What happens? - ANSWERSreflected absorbed transmitted refracted opaque- reflect or absorb (all metals) translucent- transmit a little diffuse lights transparent- transmit light you can see (all are dielectrics) What reduces transparency? What does doping create? What do impurities create? - ANSWERSRefraction at grain boundaries color Create E levels in band gap Conductivity - ANSWERSdue to a partially filled band charged particles move in an electric field piezo electric material - ANSWERSsmall change in shape, big E field
Wet- Voltage Scale, related to e- flow, easier to measure Intergranular attack - ANSWERSgrain boundaries have higher energy and more open space often corrode faster than bulk pitting - ANSWERScorrosion often concentrates at a break in the oxide film Stress corrosion cracking - ANSWERScrack grows steadily under constant stress intensity Al in NaCl brass in Ammonia Corrosion Fatigue - ANSWERSN failure decreases 4x in salt water for steels crack growth rate >> sum of corrosion and fatigue Work done in sliding against KE appears as - ANSWERSHeat friction does not depend on area Rates of corrosion - ANSWERSdriving forces and rates not the same Environment Critical!! salt breaks down protective oxide films Coefficients of friction metal-metal ceramic-ceramic metal-polymer how minimize? - ANSWERSmetal-metal: μs > 1/ ceramic-ceramic: μk< 1/ metal-polymer: μs- high, μk 1000-0. lubrication- hydrodynamic (bearings) or boundary (active organic molecules) --> prevent atom atom bonding --> reduce shear stress Oxide, __, ___,____ - ANSWERSCrack, Spalling, evaporating
Oxidation- Why do metals maintain parabolic weight gain? - ANSWERSM++ diffuses slowly and oxides slowly grow at interface Oxygen diffuses slowly and oxides grow at surface describe a magnetic core and how a transformer works - ANSWERScores- operates at low f, hysteris loss dominates, seek high magnetization How does doping effect the color of dielectric materials? - ANSWERSintroduction of impurities it creates another step in the band gap fixed energy, fixed wavelength and frequency, therefore color How avoid RADAR? - ANSWERS1) surface coating (dielectric,loss absorb rather than reflect)
- shape model of flat planes to reflect away from detector
- composite- semi transparent material dielectrics conductors or insulators? What can happen in a material that will polarize it? - ANSWERSinsulators- ceramics, alumina, silica -dipoles will spontaneously align (ferro-electric)
- an E field displaces the center of a charge of e- with respect to the nucleus and induces a dipole moment How do we know if something will fail - ANSWERSK > KIC Explain Griffith Criteria - ANSWERSFailure strength < theoretical due to defects in material that lead to stress concentrations structural metals and alloys, the activation energy for creep is equal to that of ___ - ANSWERSdiffusion- controls creep time polymers, activation energy for creep is equal to that of _____ - ANSWERSTg Order of Fracture Toughness: alumina, steel, polyurethane - ANSWERSpolyurethane (low- polymer) , alumina (ceramic), steel (high-metal)
