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1、胡远江630t立式冷挤压压力机有限元分析与改进设计Chapter2StructureandDeformationinMaterials2.1INTRODUCTION2.2BONDINGINSOLIDS2.3STRUCTUREINCRYSTALLINEMATERIALS2.4ELASTICDEFORMATIONANDTHEORETICALSTRENGTH2.5INELASTICDEFORMATION2.6SUMARRYOBJECTIVESReviewchemicalbondingcrystalstructureinsolidmaterials
2、atabasiclevel,andrelatethesetodifferencesinmechanicalbehavioramongvariousclassesofmaterials.Understandthephysicalbasisofelasticdeformation,andemploythisestimatethetheoreticalstrengthofsolidsduetotheirchemicalbonding.Understandthebasicmechanismsofinelasticdeformationduetopl
3、asticityandcreep.Learnwhyactualstrengthsofmaterialsfallfarbelowthetheoreticalstrengthtobreakchemicalbonds.2.1INTRODUTIONAwidevarietyofmaterialsareusedinapplicationswhereresistancetomechanicalloadingisnecessary.Thesearecollectivelycalledengineeringmaterialsandcanbebroadlycl
4、assifiedasmetalsalloys,polymers,ceramicsandglasses,andcomposites.SometypicalmembersofeachclassaregiveninTable2.1.Differencesamongtheclassesofmaterialsastochemicalbondingandmicrostructureaffectmechanicalbehavior,givingrisetorelativeadvantagesanddisadvantagesamongtheclasses.
5、ThesituationissummarizedbyFig.2.1.Forexample.thestrongchemicalbondinginceramicsandglassesimpartsmechanicalstrengthandstiffness(highE),andalsotemperatureandcorrosionresistance,butcausebrittlebehavior.Incontrast,manypolymersarerelativelyweaklybondedbetweenthechainmolecules,i
6、nwhichcasethematerialhaslowstrengthandstiffnessandissusceptiblecreep12胡远江630t立式冷挤压压力机有限元分析与改进设计deformation.Startingfromthesizesaleofprimaryinterestinengineering,roughonemeter,thereisaspanof10ordersofmagnitudeinsize,downtothesaleoftheatom,whichisaround10-10m.Thissituationan
7、dvariousintermediatesizescalesofinterestareindicatedinFig.2.2.Atanygivensizescale,anunderstandingofthebehaviorcanbesoughtbylookingatwhathappensatasmallerscale;Thebehaviorofamachine,vehicle,orstructureisexplainedbythebehaviorofitscomponentparts,andthebehaviorofthesecanintur
8、nbeexplainedbytheuseofsmall(10-1to10-2m)testspecimens,andthematerials.Similarly,themacros