简介:Theeffectsofisothermalholdingprocessonthemicrostructureevolutionofsemi-solid7075strengthaluminumalloyproducedbytherecrystallisationandpartialremelting(RAP)processwereinvestigated.Tensilemechanicalpropertiesofas-receivedandthixoformedalloysatroomtemperaturewereexamined.Theresultsshowthatthemicrostructureofas-receivedalloyexhibitsremarkableorientationalongthedeformationdirection.Withtheincreaseofisothermalholdingtime,thesolidparticlegrainsizecontinuouslyincreasesandthedegreeofspheroidizationalsoimproves.Coalescencemechanismisdominantwhenreheatedat595°CandOstwaldripeningmechanismisdominantwhenreheatedat615°Cinthesemi-solidstate.Alowercoarseningrateisobservedfor615°C(coarseningrateK=391μm3s-1)comparedwiththecoarseningratefor595°C(coarseningrateK=501μm3s-1).TheRAP7075aluminumalloycanbesuccessfullythixoformedandthefillingofcomponentsisgoodafterthixoforming.Thethixoformedcomponentsexhibitfavoritemechanicalproperties.
简介:Metal-semiconductor-metalphotodetectorsonsemi-insulatingGaAswithinterdigitalelectrodesshowedsignificantenhancementinthespectralresponseinthenear-infraredregionastheelectrodespacingisreduced.Thephotocurrentforthedevicewith5μminterdigitalspacingisfiveordersofmagnitudehigherthanthedarkcurrent,andtheroomtemperaturedetectivityisontheorderof2.4×1012cmHz1∕2W-1at5Vbias.Furthermore,thespectralresponseofthisdevicepossessesstrongdependenceonthepolarizationofincidentlightshowingpotentialplasmoniceffectswithonlymicroscaledimensions.Theseexperimentaldatawereanalyzedusingopticalsimulationtoconfirmtheresponseofthedevices.
简介:Aradialcrackemanatingfromasemi-circularnotchisofsignificantengineeringimportance.Accuratedeterminationofkeyfracturemechanicsparametersisessentialfordamagetolerancedesignandfatiguecrackgrowthlifepredictions.Thepurposeofthispaperistoprovideanefficientandaccurateclosed-formweightfunctionapproachtothecalculationofcracksurfacedisplacementsforaradialcrackemanatingfromasemi-circularnotchinasemi-infiniteplate.Resultsarepresentedfortwoloadconditions:remoteappliedstressanduniformstresssegmentappliedtocracksurfaces.Basedonacorrectionofstressintensityfactorratio,highlyaccurateanalyticalequationsofcracksurfacedisplacementsunderthetwoloadconditionsaredevelopedbyfittingthedataobtainedwiththeweightfunctionmethod.ItisdemonstratedthattheWuCarlssonclosed-formweightfunctionsareveryefficient,accurateandeasy-to-useforcalculatingcracksurfacedisplacementsforarbitraryloadconditions.Themethodwillfacilitatefatiguecrackclosureandotherfracturemechanicsanalyseswhereaccuratecracksurfacedisplacementsarerequired.
简介:Theearth’ssurfaceirregularitiescansubstantiallyaffectseismicwavesandinduceamplificationsofgroundmotions.Thisstudyinvestigateswhetherandhowthesourcecharacteristicsaffectthesiteamplificationeffects.Ananalyticalmodelofalinesourceofcylindricalwavesimpingingonanalluvialvalleyisproposedtolinkthesourceandsite.Theanalyticalsolutiontothisproblemprovesoneaspectofthestrongeffectofsourceonsiteamplification,i.e.,thewavecurvatureeffect.Itisfoundthatthesiteamplificationdependsonthesourcelocation,especiallyunderconditionsofasmallsource-to-sitedistance.Whetherthedisplacementisamplifiedorreducedandthesizeoftheamplificationorreductionmaybedeterminedbythelocationofthesource.Itissuggestedthattraditionalstudiesofsiteresponses,whichusuallyignorethesourceeffect,shouldbefurtherimprovedbycombiningthesourcewithsiteeffects.