ME260 Mechanical Engineering Design IIMechanical Properties of MaterialsSlide 3Slide 4PLASTIC (PERMANENT) DEFORMATIONYOUNG’S MODULI: COMPARISONYIELD STRENGTH: COMPARISONTENSILE STRENGTH: COMPARISONDUCTILITY, %ELEffect of Temperature on the Stress-Strain DiagramTOUGHNESSSlide 12HARDNESSCREEPFATIGUEDUCTILE VS BRITTLE FAILUREMECHANICAL PROPERTIESMaterial TypesAtomic Structure of MaterialsPOLYMER MICROSTRUCTURESTEELSNONFERROUS ALLOYSMaterial SelectionApplications of Material UseSlide 25Slide 26Slide 27Slide 28ME260 Mechanical Engineering Design IIInstructor notesMechanical Properties of Materials Slope is Young’s Modulus, E,indicates stiffnessUltimate Tensile Strength(UTS)Or simply Tensile Strength (TS)Yield stress,sometimes yMechanical Properties of MaterialsMechanical Properties of Materials Compression is the opposite of tension, i.e. you put pressure on the surface or push on it as opposed to pull on itThe stress-strain curve/diagram of a material subjected to compression usually looks similar to a tension testF F Area = AlF F Area = Ao lo(left) Before deformation, and (right) after deformation• Simple tension test:PLASTIC (PERMANENT) DEFORMATIONStrainStressPermanentStrainUnloadingLoading/UnloadingLoading0.280.61Magnesium,AluminumPlatinumSilver, GoldTantalumZinc, TiSteel, NiMolybdenumGraphiteSi crystalGlass-sodaConcreteSi nitrideAl oxidePCWood( grain)AFRE( fibers)*CFRE *GFRE*Glass fibers onlyCarbon fibers onlyAramid fibers onlyEpoxy only0.40.8246102040608010020060080010001200400TinCu alloysTungsten<100><111>Si carbideDiamondPTFEHDPELDPEPPPolyesterPSPETCFRE( fibers)*GFRE( fibers)*GFRE(|| fibers)*AFRE(|| fibers)*CFRE(|| fibers)*MetalsAlloysGraphiteCeramicsSemicondPolymersComposites/fibersE(GPa) Eceramics > Emetals >> Epolymers109 PaBased on data in Table B2,Callister 6e.Composite data based onreinforced epoxy with 60 vol%of alignedcarbon (CFRE),aramid (AFRE), orglass (GFRE)fibers.YOUNG’S MODULI: COMPARISONGraphite/ Ceramics/ SemicondMetals/ AlloysComposites/ fibersPolymersYield strength, y (MPa)PVCHard to measure, since in tension, fracture usually occurs before yield.Nylon 6,6LDPE7020406050100103020030040050060070010002000Tin (pure)Al (6061)aAl (6061)agCu (71500)hrTa (pure)Ti (pure)aSteel (1020)hrSteel (1020)cdSteel (4140)aSteel (4140)qtTi (5Al-2.5Sn)aW (pure)Mo (pure)Cu (71500)cwHard to measure, in ceramic matrix and epoxy matrix composites, since in tension, fracture usually occurs before yield.HDPEPPhumiddryPCPET¨Room T values y(ceramics) >>y(metals) >> y(polymers)Based on data in Table B4,Callister 6e.a = annealedhr = hot rolledag = agedcd = cold drawncw = cold workedqt = quenched & temperedYIELD STRENGTH: COMPARISONRoom T valuesSi crystal<100>Graphite/ Ceramics/ SemicondMetals/ AlloysComposites/ fibersPolymersTensile strength, TS (MPa)PVCNylon 6,6101002003001000Al (6061)aAl (6061)agCu (71500)hrTa (pure)Ti (pure)aSteel (1020)Steel (4140)aSteel (4140)qtTi (5Al-2.5Sn)aW (pure)Cu (71500)cwLDPEPPPCPET203040200030005000GraphiteAl oxideConcreteDiamondGlass-sodaSi nitrideHDPEwood( fiber)wood(|| fiber)1GFRE(|| fiber)GFRE( fiber)CFRE(|| fiber)CFRE( fiber)AFRE(|| fiber)AFRE( fiber)E-glass fibC fibersAramid fib TS(ceram) ~TS(met) ~ TS(comp) >> TS(poly)Based on data in Table B4,Callister 6e.a = annealedhr = hot rolledag = agedcd = cold drawncw = cold workedqt = quenched & temperedAFRE, GFRE, & CFRE =aramid, glass, & carbonfiber-reinforced epoxycomposites, with 60 vol%fibers.TENSILE STRENGTH: COMPARISON• strain at failure:Engineering tensile strain, Engineering tensile stress, smaller %EL (brittle if %EL<5%)larger %EL (ductile if %EL>5%)• Another ductility measure: %AR Ao AfAox100LoLfAoAf100% ooflllELAdapted from Fig. 6.13, Callister 6e.DUCTILITY, %EL• Aluminum/structural steels are examples of ductile materials whereas glass/ceramics are notEffect of Temperature on the Stress-Strain Diagram• Energy to break a unit volume of material• Approximate by the area under the stress-strain curve.• Toughness can be measured with an impact test (Izod or Charpy)smaller toughness- unreinforced polymersEngineering tensile strain, Engineering tensile stress, smaller toughness (ceramics)larger toughness (metals, PMCs)TOUGHNESSToughness can be measured with an impact test (Izod or Charpy)TOUGHNESS• Resistance to permanently indenting the surface.• Large hardness means: --resistance to plastic deformation or cracking in compression. --better wear properties.e.g., 10mm sphereapply known force (1 to 1000g)measure size of indent after removing loaddDSmaller indents mean larger hardness.increasing hardnessmost plasticsbrasses Al alloyseasy to machine steels file hardcutting toolsnitrided steels diamondAdapted from Fig. 6.18, Callister 6e. (Fig. 6.18 is adapted from G.F. Kinney, Engineering Propertiesand Applications of Plastics, p. 202, John Wiley and Sons, 1957.)HARDNESS• Occurs at elevated temperatures, normally T > 0.4 Tmelt• Deformation changes with time• Examples: turbine engine bladesCREEPDeformation with time• Fatigue = failure under cyclic stress.• Stress varies with time.• Key points: Fatigue... --can cause part failure, even though  < y. --causes ~ 90% of mechanical engineering failures. FATIGUEHip implant-cyclicloading from walking.Adapted from Fig. 17.19(b), Callister 6e.Ship-cyclic loadingfrom waves.Adapted from Fig. 8.0, Callister 6e. (Fig. 8.0 is by Neil Boenzi, The New York Times.)• Ductilefracture isdesirablefor structural applications!• Classification:Ductile: warning before fracture, i.e. changes geometry before failureBrittle: No warningAdapted from Fig. 8.1, Callister 6e.DUCTILE VS BRITTLE FAILUREVery DuctileModerately DuctileBrittleFracture behavior:Large Moderate%AR or %EL:SmallMECHANICAL PROPERTIESHardStrong Brittle (not Tough)The following associations normally apply:Ductile (Tough) Soft(er)Weak(er) (not strong)Material Types Ferrous metals/alloysNonferrous metals/alloysPolymersCeramicsGlassDiamond, GraphiteWoodCompositesIron-based materials, e.g. steelsBoth made from pure carbonbut have different atomic structurePlastics and rubber are prime examplesCompounds of metallic & nonmetallic elements, e.g. chinawareNatural and organic materiale.g. nickel, silver, etc.A combination of two/more material typesSolid with a random atomic structure like a fluidAtomic Structure of Materials Ferrous metals/alloysNonferrous