Effect of lateral impact loads on failure of pressurized pip(4)

196CSNgandWQShen

whenitwassubjectedtoaconstantcon ningpressureandstrain-controlledaxialloading,wherenochangeintotalmoisturecontentwasallowed.Themaximumstrengthofthekaolinoccurredatthemoisturecontentof24.5percent.Atypicalresultforthesoilspecimenwithamoisturecontentof47.77percentwasusedto ndoutthepropertiesofthepresentkaolinfoundation.Thevaluefortheinitialtangentmoduluswascalculatedtobe4.4MN/m2.Poisson’sratioof0.5wasusedinthiscaseandwassubjecttothevolumeofthekaolinfoundationremainingconstantaftertheimpactloading[14].

2.3Methodology

Thisexperimentwasconcernedwiththebehaviourofaconsiderablylonguniformgaspipelineundertheactionofsingletransverseloadingactingatthetopsurface.Thepipespecimenswerefullyclampedacrossaspanof2Latbothends,aswellaswithandwithoutafoundationsupportalongtheunderneathofthepipe,asshowninFig.3aandb,respectively.Thepipesweredesignedtofreelymovealongthelongitudinaldirectionatthesupports.Thepipesweresubjectedtoalateralimpactloadingatthemid-spaninthedirectionperpendiculartothepipeaxisbyarigidwedge-shapedindenter,whichhadacylindricalimpactsurfaceofradius2.65mmatthetipandamassofG¼80kgwasusedforallthetests.Notethatthelengthoftheindenterinthedirectionperpendiculartothepipeaxiswaslongerthanthehalfcirclelengthofthepipe.

Inordertoexaminethein uenceoffoundationsoncriticalinitialimpactenergy,threedifferent

majorgroupsoffoundationsupportforthepipespecimenswereconducted.TheyweregroupsA,B,andCforthesandfoundation,kaolinfoundationandnon-foundation,supports,respectively.Assump-tionsweremadesuchthatthefoundationprovidedaperfectlinesupportforthepipe.Alinesupportdoesnotdiffersigni cantlyfromasupporthaving 308contactwiththepipe,asshowninFig.4[1].

Nitrogengaswasusedtoachievetheinternalpressureinthepipes,ratherthanusingrelativelyincompressiblewater,assuggestedinreference[5].Thiswasduetoadecreaseinasmallamountinpipevolumethatwouldcauseanincredibleincreaseinpressureactingontheinnersurfaceofthepipe,ifwaterwasused.Inordertoexaminethein uenceofpressuresonthecriticalinitialimpactenergy,threedifferentvaluesofinternalpressurewereused,i.e.63bars(su¼0.136sy),95bars(su¼0.207sy)and125bars(su¼0.272sy).Thesewereinadditiontotheimpacttestswithoutinternalpressureinsidethepipe.Internalpressuresbeforeandafterimpacttestswererecordedforthepurposeof ndingoutthedifferencesbetweenthem.

2.4Impacttestsresults

Atotalof52identicalpipespecimensfrom12groupsofdifferentinternalpressuresandfoundationsup-portswereconducted.Theinitialimpactvelocityrangedupto7.70m/sandcausedpermanentinelas-ticdeformationforlowervelocitiesandfailureoccur-ringneartheendsupportsforhighervelocities,whichwerestudiedinreferences[3,5,6].

ThedatarecordedonthepipespecimensfromgroupsAtoCthroughouttheimpacttestsarelistedinTables1to3forthesandfoundation,kaolinfoun-dation,andnon-foundation,respectively.Thevaluesofharethedropheightoftheindenter;poandp1theinternalpressuresbeforeandaftertheimpacttests;Votheinitialimpactvelocityoftheindenterjust

2

beforestrikingthepipespecimen;Ek¼GVo/2denotestheinitialimpactenergy;PmaxandPmeanarethemaximumandaverageimpactloadings;nthenumberofreboundsoftheindenterafter

striking

Fig.3

Afullyclampedpipesubjectedtoanimpactloadingatthemid-spanposition:(a)withafoundationsupportand(b)withoutafoundation

support

Fig.4

Foundationsupports(drawingsarenottoscale):(a)perfectlinesupportand(b) 308curvesupport

JPME97#IMechE2006

Proc.IMechEVol.220PartE:J.ProcessMechanicalEngineering