关于力的外文文献翻译中英文翻译.docx
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关于力的外文文献翻译中英文翻译.docx
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关于力的外文文献翻译中英文翻译
五、外文资料翻译
StressandStrain
1.IntroductiontoMechanicsofMaterials
Mechanicsofmaterialsisabranchofappliedmechanicsthatdealswiththebehaviorofsolidbodiessubjectedtovarioustypesofloading.Itisafieldofstudythatisknownbyavarietyofnames,including“strengthofmaterials”and“mechanicsofdeformablebodies”.Thesolidbodiesconsideredinthisbookincludeaxially-loadedbars,shafts,beams,andcolumns,aswellasstructuresthatareassembliesofthesecomponents.Usuallytheobjectiveofouranalysiswillbethedeterminationofthestresses,strains,anddeformationsproducedbytheloads;ifthesequantitiescanbefoundforallvaluesofloaduptothefailureload,thenwewillhaveobtainedacompletepictureofthemechanicsbehaviorofthebody.
Theoreticalanalysesandexperimentalresultshaveequallyimportantrolesinthestudyofmechanicsofmaterials.Onmanyoccasionwewillmakelogicalderivationstoobtainformulasandequationsforpredictingmechanicsbehavior,butatthesametimewemustrecognizethattheseformulascannotbeusedinarealisticwayunlesscertainpropertiesofthebeenmadeinthelaboratory.Also,manyproblemsofimportanceinengineeringcannotbehandledefficientlybytheoreticalmeans,andexperimentalmeasurementsbecomeapracticalnecessity.Thehistoricaldevelopmentofmechanicsofmaterialsisafascinatingblendofboththeoryandexperiment,withexperimentspointingthewaytousefulresultsinsomeinstancesandwiththeorydoingsoinothers①.SuchfamousmenasLeonardodaVinci(1452-1519)andGalileoGalilei(1564-1642)madeexperimentstoadequatetodeterminethestrengthofwires,bars,andbeams,althoughtheydidnotdevelopanyadequatetheories(bytoday’sstandards)toexplaintheirtestresults.Bycontrast,thefamousmathematicianLeonhardEuler(1707-1783)developedthemathematicaltheoryanyofcolumnsandcalculatedthecriticalloadofacolumnin1744,longbeforeanyexperimentalevidenceexistedtoshowthesignificanceofhisresults②.Thus,Euler’stheoreticalresultsremainedunusedformanyyears,althoughtodaytheyformthebasisofcolumntheory.
Theimportanceofcombiningtheoreticalderivationswithexperimentallydeterminedpropertiesofmaterialswillbeevidenttheoreticalderivationswithexperimentallydeterminedpropertiesofmaterialswillbeevidentasweproceedwithourstudyofthesubject③.Inthissectionwewillbeginbydiscussingsomefundamentalconcepts,suchasstressandstrain,andthenwewillinvestigatebathebehavingofsimplestructuralelementssubjectedtotension,compression,andshear.
2.Stress
Theconceptsofstressandstraincanbeillustratedinelementarywaybyconsideringtheextensionofaprismaticbar[seeFig.1.4(a)].Aprismaticbarisonethathascrosssectionthroughoutitslengthandastraightaxis.InthisillustrationthebarisassumedtobeloadedatitsendsbyaxisforcesPthatproduceauniformstretching,ortension,ofthebar.Bymakinganartificialcut(sectionmm)throughthebaratrightanglestoitsaxis,wecanisolatepartofthebarasafreebody[Fig.1.4(b)].Attheright-handendtheforcePisapplied,andattheotherendthereareforcesrepresentingtheactionoftheremovedportionofthebaruponthepartthatremain.Theseforceswillbecontinuouslydistributedoverthecrosssection,analogoustothecontinuousdistributionofhydrostaticpressureoverasubmergedsurface.Theintensityofforce,thatis,theperunitarea,iscalledthestressandiscommonlydenotedbytheGreekletterб.Assumingthatthestresshasauniformdistributionoverthecrosssection[seeFig.1.4(b)],wecanreadilyseethatitsresultantisequaltotheintensityбtimesthecross-sectionalareaAofthebar.Furthermore,fromtheequilibriumofthebodyshowinFig.1.4(b),
Fig.1.4Prismaticbarintension
wecanalsoseethatthisresultantmustbeequalinmagnitudeandoppositeindirectiontotheforceP.Hence,weobtain
б=P/A(1.3)
astheequationfortheuniformstressinaprismaticbar.Thisequationshowsthatstresshasunitsofforcedividedbyarea--------forexample,Newtonspersquaremillimeter(N/mm²)orpoundsofpersquareinch(psi).WhenthebarisbeingstretchedbytheforcesP,asshowninthefigure,theresultingstressisatensilestress;iftheforcearereversedindirection,causingthebattobecompressed,theyarecalledcompressivestress.
AnecessaryconditionforEq.(1.3)tobevalidisthatthestressбmustbeuniformoverthecrosssectionofthebat.Thisconditionwillberealizediftheaxialforcepactsthroughthecentroidofthecrosssection,ascanbedemonstratedbystatics.WhentheloadPdosesnotactatthuscentroid,bendingofthebarwillresult,andamorecomplicatedanalysisisnecessary.Throughou
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