Effect of lateral impact loads on failure of pressurized pip(13)

Effectoflateralimpactloads205

Itwasassumedthattheimpactloadingandtheinternalpressurewouldacttogethertothepipesimultaneously.Twosolidsteelbungswereusedintheinvestigationinordertopreventthedistortionofthepipewithintheclamps.Thepressureinthepipesputforceontothebungsandtriedtoelongatethepipes.TheeffectofthepressureactingonthebungswasneglectedinthepresentFEA.

Someofthesigni cantnumericalresultsarerecordedinTable7andcomparedwiththeimpacttestsresults.Thecorrespondingvaluesfromtheimpacttestsarealsopresentedinthetableforcom-parison.Asmentionedinsection2,thepipeswerefreetomovealongthelongitudinalaxisduringtheimpacttests.Therewerestillsomerestrictionsonthepipeswithintheclampsduringtheimpacttests.Linearelasticisotropicmaterialpropertieswereassignedtothefoundationsinthenumericalmodel-ling.Therefore,thefoundationsreactedelasticallyandthedeformationofthefoundationwouldhaverecoveredduringtheimpactloading.BecauseofthisthevaluesofCfintheFEpredictionswerealwayslessthantheexperimentaltestsresults,asshowninTable7.

ShenandChen[7]proposedanempiricalformulafordeterminingthecriticalmeanplastichingelengthaslpc¼2Rl1.ThevaluesoflpobtainedfromtheFEAasrecordedinTables4to6werecomparedwiththevalueoflpc,whichisequalto47.31mm.Itwasfoundthatthevaluesoflpforthepresentspecimensweremuchlowerthantheempiricalvalueoflpc,i.e.,50percent.Thiswasduetotheeffectofthesup-portconditionasthepresentspecimenswerefreetomoveintheaxialdirection.Foracertainimpactenergyactinginsideapipe,aplasticenergydensityofthepipenearasupportincreaseswiththedecreasesintheplastichingelength,whichcausesthepipebecomeweaker.Thisiswhythevaluesoflcforthepresentunpressurizedpipeswerelowerthanthosefortheunpressurizedpipereportedinreference[5],asshowninFig.8.5

CONCLUSION

deformationpro leofthestructuresinthethree-dimensionaldynamicnon-linearFEAwereobtained.Thein uencesofthecircumferentialstressbecauseoftheinternalpressure,foundationsupport,andthemembraneforceonthethresholdoffailureforthepipelinesweresigni cant.Hence,thepre-viousresearchonthepipelineswithoutafoundationsupportmaynolongerbevalidfortheactualpipelineswithafoundationsupport.

Furtherexperimentaltestsneedtobecarriedoutinordertoobtaintheplasticbehavioursoffoun-dations,suchastheinitialcohesion,theinitialand nalfrictionangles,andthelimitingplasticstrain.Moreunderstandingofthephenomenawillbegainedfromtheproposedtheoreticalworkinthefuture,especiallytofurtherdevelopthetheoreticalstudyproposedinreference[8].Thein uencesofinternalpressureloading,foundationsupport,membraneforces,andthepropertiesofthematerialsinordertopredicttheinelasticresponseandtheonsetoffailureforthepipelinesshouldbeconsidered,asshouldtheroleoftheindenteronthedynamicresponseandthegeometricalscalinglaw.

REFERENCES

1Leis,B.N.,Francini,R.B.,Mohan,R.,Rudland,D.L.,andOlson,R.J.(1998).Pressure-displacementbeha-vioroftransmissionpipelinesunderoutsideforces–towardsaserviceabilitycriterionformechanicaldamage.ProceedingsoftheEighth(1998)InternationalOffshoreandPolarEngineeringConference,Canada,1998,pp.60–67.

2Thomas,S.G.,Reid,S.R.,andJohnson,rgedeformationsofthin-walledcirculartubesundertrans-verseloading–I:anexperimentalsurveyofthebend-ingofsimplysupportedtubesunderacentralload.Int.J.Mech.Sci.,1976,18,325–333.

3Jones,N.,Birch,S.E.,Birch,R.S.,Zhu,L.,andBrown,M.Anexperimentstudyonthelateralimpactoffullyclampedmildsteelpipes.Proc.InstnMech.Engrs,PartE:J.ProcessMechanicalEngineering,1992,206,111–127.

4Jones,N.andShen,W.Q.Atheoreticalstudyofthelat-eralimpactoffullyclampedpipelines.Proc.InstnMech.Engrs,PartE:J.ProcessMechanicalEngineering,1992,206,129–146.

5Jones,N.andBirch,R.S.In uenceofinternalpressureontheimpactbehaviorofsteelpipelines.Trans.ASMEJ.Press.VesselTechnol.,1996,118,464–471.

6Chen,K.S.andShen,W.Q.Furtherexperimentalstudyonthefailureoffullyclampedsteelpipes.Int.J.ImpactEng.,1998,21(3),177–202.

7Shen,W.Q.andChen,K.S.Aninvestigationontheimpactperformanceofpipelines.Int.J.Crashworthiness,1998,3(2),191–209.

Experimentaldatarecordedfromatotalof52impacttestsontheseamlessmildsteelpipeswithandwith-outafoundationsupportarepresentedinthisarticle.Thepipespecimenswithdifferentinternalpressureloadingsthatproducecircumferentialstressesupto0.272sywereconducted.

Numericalsimulationsoftheexperimentaltestswereconducted.Thesenumericalsimulationswerecarriedoutthroughathree-dimensionaldynamicnon-linearFEA,whereboththegeometricalandmaterialnon-linearitieswereconsidered.Thedetailsofthestressandstraindistributionsandthe

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