对金属弹塑性断裂试验研究英文论文.docx
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对金属弹塑性断裂试验研究英文论文.docx
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对金属弹塑性断裂试验研究英文论文
σ1CTestandStudyonPlastoelasticFractureofMetallicMaterialsandItsCriterionStrengthStress
(对金属弹塑性断裂试验研究)
Abstract
Bytheanalysisonfracturestrengthmechanicsperformancesofmaterialitself,thepaperhasderivedafracturestrengthstresscriterionparameter--σ1CtotheItypeofcrack(opentype)onthemetallicmaterial,whichissimilarasthematerialparametersofyieldstrengthvaluesandtensilestrengthvalueσb.Itcouldbeascertainedthroughthetestandcouldbeaccuratelyusedtoevaluatematerials,quantitativeengineeringdesignandtopreventthehappeningsoffractureaccidentsintheengineeringstructures.
KeyWords:
MetallicMaterial,FractureCriterion,StrengthStress--σ1C.
1,FractureMechanicsPerformancesofMaterial
Fracturemechanicsbeganfromthestudyonlowstressbrittleruptureofglassin20’sof20centurybyMr.Griffith,andthencontinuouslybyMr.Zener,Mr.Hollmon,Mr.Irwin,Mr.WellsandMr.Riceetc.Untilpresent,nomatterwhatideasandmethods,thestudyanddevelopmentonfracturemechanicsistouseamechanicsperformanceofmaterialitselfasthereferencevalue,toreachthepurposesofevaluatingmaterials,engineeringdesignandpreventingthehappeningsofengineeringfractureaccidents.Butthecorefoundationofstudyisthemechanicsperformancesofmaterialitself.
Whatarethefracturemechanicsperformancesofmaterials?
Whatqualificationsarenecessarytoconducttheaccurateevaluationonmaterials,engineeringquantitydesignandpreventingthehappeningsoffractureaccidentsinengineeringstructure?
First,whatisthemechanicsperformanceofmaterialitself?
Thedefiniteanswerisundertheeffectofexternalforces(externalcauses),behaviorsrepresentedbytheinternalstructure(internalcauses)ofmaterial.Basedonthisdefinition,thecrack-likeflawinamainpresumeoffracturemechanicshasalreadyexistedlongtimebefore,anditisrupturedundertheeffectofexternalforces.Thefracturestrengthperformancesofmaterialarethebehaviorsofmechanicsperformancesofinternalstructureintheareaofcracktipundertheeffectofexternalforces.Thereareseveralfollowingissuesneedtobediscussed:
1),Whenthechemicalcompositionofmaterialissame,heatingprocessissame,themicrocosmicstructureandmacrocosmicstructureofmaterialarethesame,thatistheinternalstructureissame,then,themechanicsperformancesofmaterialitselfshallberelativelythesame.
2),Forinstance,apieceofmetalplate,acracklength“a”exists(seeFigure1),theinternalstructureofmaterialinsidethesectionABisthesame.Undertheeffectofexternalforces,afterthecrackextendsthroughsectionAB,thedamagedinternalstructureofmaterialinsidethesectionABisstillthesame.Then,whencrackpassesthroughthesectionAB,everypointreleasesthesameenergy.
Figure1
3),Analysisfromthecracktipplasticarea,whencrackexistsinthematerial,thereshouldbeplasticareaexistedinthecracktip.Isthereanyboundaryfortheplasticarea?
Ifthereisnot,thecrackwillnotbeunstable.So,obviously,andiscertainthatthereisboundaryfortheplasticarea.AsFigure1showsthatundertheeffectofexternalforces,thecrackextendedandwhenisunstableatpointAorpointB,everypointshallreleasethesameenergy.
Whenthechemicalcompositionsofmaterialaresameandtheheatingprocessisdifferent,thecracktipplasticareasarealsodifferent,andreleasedifferentenergy.
Thefundamentaldevelopmentruleofmattersisthattheexternalcauseisconditionandtheinternalcauseisthebase.Theaboveanalysesshowthat:
whenthechemicalcompositionofmaterialissame,heatingprocessissame,themicrocosmicstructureandmacrocosmicstructureofmaterialarethesame,thatistheinternalstructureissame,then,thecracksorflawsexistedinthematerialarealsothesame.Whenthecracksextendedorrupturedundertheeffectofexternalforces,thestrengthperformancesofnaturalmaterialcracktipresisting(restricting)theextendingorrupturingcracksshallbeainvariablenessmechanicsperformancesconstantparameter,assameastheyieldstrengthvalues(ornominalyieldvalueσ0.2)andextensionstrengthvalueσbetc.ofmaterial.
Peoplesupposingtoachievethepurposeofevaluatingmaterial,engineeringdesignandpreventingthehappeningsofengineeringruptureaccidentsbyamechanicsperformanceparameterofmaterialitself.Thismechanicsperformanceparametershallbeachievedbytestundertherelativeconditionsandmustbeaconstantparameter.Nooneofthebothismissed,sothattheevaluatingmaterialandquantificationalapplicationinengineeringcouldbeprecisely.
2,TheParameterandTestProposalofITypeFractureStrengthStressMechanicsPerformance
Mostoftheengineeringstructuresarerupturedonthemembers’damagemainlyundertheextensionalstress.ThispaperisonlytoanalyzeandstudytherupturesofItypecrack.IntheanalysisandstudyofItypecrack,thetipplasticarea,plasticdeformation,passivationofcracktip,stressdistributionofcracktipetc.arenotdetailedstudied,sincewhentheengineeringrupturehappens,itsmaterialqualityisascertain,theplasticareaofcracktip,elasticareaandexternalforcesareascertain.Alltheseexistingcracksintheengineeringmaterialsanddistinguishingifareharmfulornotarethefutureimportantstudyissues.FortheItypeoffractures.Largeamountofstudieshavefoundmanylargerthan0.1mmcracks,throughgrandnesspointofviewtofindoutasuitablemethodtoconfirmbytestthecracktipfracturestrengthstressofmaterial,toreachthepurposeofaccuratelyevaluatematerialortoresolvequantificationallytheengineeringstructureruptureaccidents.Thefollowingissueswouldbediscussedbytheauthor:
1),Crackisextendedorruptured,largerorsmallplasticareasarealwaysproducedonthecracktipandboundarycanbefound.Thecracktipplasticareaissurroundedbymanyelasticareas,andtheplasticareasaretosmallandcanbeneglected,itisonlytheissueofgrandnessruptureofelasticplanestrainofmaterial,whichisconsistentwiththeactualengineeringstructurestatus,andtheanalysisonItypeofrupturebecomesimplerinthisway.
2),ThecrystallatticeconstantparameterofmetallicmaterialsisA0=10-7mm,normalcrystalistosmalltobeseenbynakedeyes,andthecrystalitselfisirregularinshape.Studymetallurgyfrommicrocosmichaspracticalsignificancetoimprovethematerialperformances,butfortheissuesofexistingcracksofengineeringmaterialgeneratinggrandnessrupture,itisratherdifficulttostudytheengineeringstructuregrandnessrupturefromthecrystalstructure,andnopracticalsignificance,sothestudyshouldbestartedfromthegrandness.
3),Amagnitudeassumesoffracturemechanicsofcrackshapedflawexistsinthematerialalready.ForItypeofcrackundertheexternalforces,thereisstressconcentrationparameteronthecracktip,andthiscanbeanalyzedbymathematicalandmechanicalmethod.InFigure2,a,b,carethesamespecimen,undertheexternalforces,thecracksextendedtoa1 Fig2,a,b,c Basedontheanalysisoffracturestrengthmechanicsperformanceandtheconditionsprovidedandtheaboveviewpoint,concludingthemovementandunstablenessofexistingcracksundertheexternalforces,andbyelasticmechanics,anewstrengthconstantparameteroffracturestrengthstresshasbeenintroduced.Andjustlikeyieldstrengths,extensionlimitstrengthσbofmaterialetc.shouldbeachievedbytest.Now,theyarenamedasyieldstressvalueofmaterialfracturestrength0andstressvalueofmaterialfracturelimitstrength(damaged)c.AndItypeofcracksexist,theyarenamedas10and1Crespectively.Thestressvalue(damaged)ofItypefracturelimitstrength1Cisthefollowingmainstudyissue. Inordertofurtherapprovetherealityofthefracturestrengthstressofmaterial1Cisacomparativelyconstantparameter,thedetailtestproposalisdesignedasfollowing: 1),Inordertominimizethedispersivenessoffinaltestresults,allofthespecimenmaterialsforthestructuresteeltestarefromthesamemetalplate. 2),Inordertocomparetheinfluencestothefinaltestresultsbydifferentgeometrydimensionsofspecimen,thespecimensareprocessedasdifferentdimensionsrespectivelyinlengthL,heightWandthicknessB. 3),Inordertocomparetheinfluencestothefinaltestresultsbydifferentprearrangedgapsanddifferentprearrangedgaplengths,theprearrangedgapsbeforespecimensinducednaturalcracks,twodifferentmethodsandtwodifferentlengthsoflinearcuttingandmanualsteelsawingareapplied. 4),Inordertocomparetheinfluencestothefinaltestresultsbydifferentcracklengths,differentnaturalcracksareinducedineveryspecimen. 5),Inordertocomparetheinfluencestothefinaltestresultsbythecracksinspecimensindifferentgeometrydimensions,differentnaturalcrackslengthsareinducedineveryspecimen. 6),Inordertoguaranteetherelativelyveracityandcomparabilityoftestresults,three-pointsbendingmethodwillbeuseduniformlyinthetest. 7),Inordertoeliminatetheinfluencestothefinaltestresultsby
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