Low velocity impact behavior of composite sandwich panels(3)

Thecoreusedforthesandwichpanelwasaclosed-cellPVCfoam(DivinycellH250obtainedfromDIAB).Thisfoamisrelativelydensecomparedtoothercommonlyusedfoamsforcorematerials.Thecorewas25.4mmthick.Table2listsselectedmechanicalpropertiesofDivinycellH250.

Table1

In-planemechanicalpropertiesofcarbonfabric/epoxycompositeusedforsandwichfacesheets[18]Property

ValueDensity,r(kg/m3)

1600

Fibervolumeratio,Vf(%)62Warpmodulus,E1t(GPa)77Fillmodulus,E2t(GPa)75MajorPoisson’sratio,n12

0.07In-planeshearmodulus,G12(GPa)6.5Out-of-planeshearmodulus,G31(GPa)5.1Out-of-planeshearmodulus,G32(GPa)4.1Warptensilestrength,F1t(MPa)963Ultimatewarp, lltensilestrain,3ult1t;2t(%)

1.3

Table2

Selectedmechanicalpropertiesofsandwichcorematerial:DivinycellH250Property

ValueDensity,r(kg/m3)

250In-planemodulus,E1(MPa)240Out-of-planemodulus,E3(MPa)

403Transverseshearmodulus,G13(MPa)115In-planecompressivestrength,F1c(MPa)4.6Transverseshearstrength,F13(MPa)

5

ThesandwichpanelwasfabricatedbybondingthecuredfacesheetstothecorematerialwithHysol9430adhesive,aroomtemperaturecuringepoxyresin.Thefacesheetsandcorewerebondedtogetherandcuredundervacuum.The nalsandwichpanelwasasquareplateof27.9!27.9cmdimensionswithanoverallthicknessof2.82cmandamassof0.83kg(Fig.1).Threeplateswerefabricatedforthisstudy,oneforquasi-statictestingandtwoforimpacttesting.2.2.Quasi-statictesting

Todeterminetheleveltowhichdynamicprocessesshouldbeconsideredinlowvelocityimpacttesting,asandwichpanelwas rsttestedunderaquasi-staticloadingforsubsequentcomparisonwiththeimpactloadingcase.Thecomparisoninvolvescorrelatingloadandstrainlevelsbetweenthetwotypesoftests.Inbothloadingsituations,thesandwichpanelwassimplysupportedonrollersalongtwoparalleledges.Thesupportsweresteelbarsof25.4mmdiameterandwere rgelocalstrainscausedbyindentationcaninduceearlyfailureofthesandwichfacesheet[19].

Thepanelwasinstrumentedwith16straingagesatvariouslocationsonthetopandbottomfacesheets.SelectedstraingagelocationsareshowninFig.2.Thede ectionofthesandwichplateattheloadpointwasrecordedbythestrokeoftheInstronservo-hydraulicmachine,whichalso

Fig.1.Photographof nishedcompositesandwichpanel.

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