资源描述：
《Lesson13MechanicalShockTheory第13课机械冲击理论.ppt》由会员上传分享，免费在线阅读，更多相关内容在工程资料-天天文库。
1、Lesson13 MechanicalShockTheory第13课机械冲击理论IntroductionThroughoutthedistributionsystem,packagesaremanhandledandmishandledinvariousways:dropped,thrown,kickedandotherwiseroughlyabused;fallfromconveyorsorforkliftsandcrashtothefloor;subjectedtoavarietyofvehicleimpacts;trucksstarting,stoppi
2、ng,hittingchuckholesandrailroadcrossings,railcarhumping,joltingandothermoderatelyviolentactions;suffersanimpactwithanotherobject：floor,truckbed,pallet,bulkheadoranotherpackage.Amechanicalshockoccurswhenanobject'sposition,velocityoraccelerationsuddenlychanges.Suchashockmaybecharacter
3、izedbyarapidincreaseinaccelerationfollowedbyarapiddecreaseoveraveryshortperiodoftime.Figure13.1:theaccelerationversustimeplotformostshocksFigure13.1RepresentationofmechanicalshockApackageshockmaytypicallybe20milliseconds(0.020seconds)longandhaveamagnitudeor"height"of150g's. needtokn
4、owboththemagnitudeoftheaccelerationandthedurationoftheshock.TheFreeFallingPackagethelengthoftimeittakesapackagetofallfromadropheight,hthedownwardvelocityatwhichitwillbetravelingamomentbeforeimpact;,theimpactvelocity:AsisshowninFigure13.2.Apackagewillreboundalittleoralotdependingonth
5、enatureofthepackageandthesurfaceithits.Figure13.2Afallingpackagecoefficientofrestitution,e,describesthereboundvelocityasafunctionoftheimpactvelocity 13.1 totalvelocitychange: 13.2 13.3 Because01(typicalvaluesfallinginthe0.3to0.5range): 13.4 velocitychangeisalsonumericallyequalto
6、theareabeneaththeshockpulseasshowninFigure13.3.Figure13.3TherelationshipamongshockparametersPackagedamageisrelatedtothethreefactorsinvolvedinmechanicalshock:PeakAccelerationDurationVelocityChangeMechanicalShockTheoryShowninFigure13.4,theproduct-packagesystemconsistsoffourbasiccompon
7、ents:theoutercontainer,thecushion,theproduct,andacriticalelement.showninFigure13.5:theproduct-packagemodel:Figure13.4Asimpleproduct-packagesystemFigure13.5Aspring-massmodelfortheproduct-packagesystemM2-themassoftheproductM1-representsthemassofthecriticalelementorCEM3-representsthema
8、ssoftheoutercontain
