LS-DYNA负体积解决方法(英文版本)

NegativeVolumeinFoamsLS-DYNAENVIRONMENTLS-DYNAENVIRONMENTOct2010PreventingNegativeVolumeSolidElementsinFoamMaterialsNegativeVolumeinFoamsLS-DYNAENVIRONMENTNegativevolumeerrorsAtypicalerrorthatcanoccurwhenmodellingafoammaterialsubjectedtohighloadsandalargeamountofcompressionisnegativevolumeinthesolidelements.Thisiswereonefaceofasolidelementpassesthroughtheotherface.N1N2N3N4N1N2N3N4N1N2N3N4NegativeVolume110000t2.7432E-02dt4.38E-09flushi/obuffers115000t2.7454E-02dt5.81E-09flushi/obuffers***Errornegativevolumeinsolidelement#3719cycle119373***Errorcomplexsoundspeedinsolidelement#3719cycle119373ErrorreportfromthelogfileNegativeVolumeinFoamsLS-DYNAENVIRONMENTSolution1–ModifyingthefoamstiffnessOnemethodtosolvethisproblemistoincreasethestiffnessofthefoammaterialasitstartstolockupatabout80-90%crush(strain=0.8-0.9).Thisisdonebyeditingthestress-straincurveusedforthefoammaterial.σεσε0.8NegativeVolumeinFoamsLS-DYNAENVIRONMENTSolution2–NullshellsAnothermethodistoputalayerofnullshellonthetopandbottom(front/back)facesofthefoam.Acontactbetweenthesetolayersofnullshellsisthenusedtopreventthesolidelementsfrombecomingtoocompressed.Thecontactthicknessbetweenthetwoplatesissettoabout10%ofthethicknessofthefoamblocksothatthecontactwillacttolockupthefoamblockat90%crush.NullShellNullshellsareshellelementsthatuse*Mat_Null.Coatingsolidelementswithnullshellsiswhenashellelementiscreatedonasolidelementfacesharingthesamenodesasthesolidelement.TypicalpropertiesDensity=0.1*foamdensityYoungsModulus=1GpaThickness=1mmToplayerofnullshellsBottomlayerofnullshellsFoamBlockNegativeVolumeinFoamsLS-DYNAENVIRONMENTTetrahedronElementsIfthefoamhasbeenmeshedwithtetrahedron(tet)elements,thenthestabilitycanbeimprovedbymakingsurethetetelementsgeneratedarereasonablyregularandnotskewedover.GoodOKBadNegativeVolumeinFoamsLS-DYNAENVIRONMENTExampleModel–BaseInthisexampleablockoffoamiscrushedbya20kgplateimpactinga3m/s.Themodelfallsoverat38.6msecduetonegativevolumeinthesolidelements.NegativeVolumeinFoamsLS-DYNAENVIRONMENTExampleModel–Solution1Thestress-straincurveforthefoammaterialhasbeenmodifiedtopreventthenegativevolumes.ContactforceresultsshowingboththeloadingandunloadingphaseOriginalmodelwiththeerrorModelwithincreasedfoamstiffnessNegativeVolumeinFoamsLS-DYNAENVIRONMENTExampleModel–Solution2ThehighpeakloadseenwhenthetopandbottomlayerscomeintocontactcanbereducedbyloweringtheYoung’smodulusofthenullshells,thecontactthicknessmayalsoneedtobeincreasedtopreventthecontactfromfailing.(e.g.100MPaand15mm)Nullshellshavebeencreatedonthetopandbottomsurfacealongwithacontactbetweenthem.ContactforceresultsshowingboththeloadingandunloadingphaseOriginalmodelwiththeerrorModelwithincreasednullshellsaddedNegativeVolumeinFoamsLS-DYNAENVIRONMENTContactInformationUK:ArupTheArupCampusBlytheValleyParkSolihull,WestMidlandsB908AEUKT+44(0)1212133399F+44(0)[e-mail]asecontactthefollowing::Arup39/F-41/FHuaiHaiPlazaHuaiHaiRoad(M)[e-mail]:nHanceEngineeringSolutionsPvt.Ltd(Arup)AnanthInfoParkHiTecCityMadhapurHyderabad-500081IndiaT+91(0)4044369797/[e-mail]