Preparation And Properties Of Al₂O₃/ductile Interlayer/epoxy Laminated Composites

The toughness of laminated composites with ductile interlayers is improved mainly byplastic deformation of the interlayers,which lead to crack blunting, crack capturing and crackbridging in ductile interlayers.In this thesis, with epoxy resin adhesives as binder, ceramic,metal and polymer are combined to fabricate Al₂O₃/Al, Al₂O₃/Nylon/Al andAl₂O₃/steel-epoxy laminated composites using mould pressing method at room temperature.The microstructures, mechanical properties, load-displacement curves and crack paths ofthese composites were analyzed, and the machanism of crack propagation was discussed. Thewater resistance, acid resistance and alkali resistance of Al₂O₃/steel-epoxy composites weretested.In order to determine the addition content of curing agent, the bond strength and themechanical properties of epoxy resin adhesives with various mass ratios of epoxy resin tohardener, namely1:0.7,1:0.8,1:0.9and1:1.0, were investigated. The results indicate that thebond strength reaches its maximum when the mass ratio is1:0.8, and the correspondingcuring system can get a better mechanical performance. So, the mass ratio of epoxy resin tohardener is decided to1:0.8.Al₂O₃as ceramic layer, Al slice as interlayer, epoxy resin adhesives as binder, laminatedAl₂O₃/Al composites were fabricated via a simple moulding process at room temperature and5MPa, with epoxy resin adhesives as the binder. Microstructure analysis results show that theinterfaces of Al₂O₃/epoxy/Al bond tightly with a2⁵μ adhesives thickness. Moreover,mechanical test results show that, the fabricated composites, compared with Al₂O₃monolith,have a slightly lower bending strength but much higher fracture toughness and fracture work,which is attributed to the multiple fractures during the crack propagation.In view of the fact that thin adhesives layer in Al₂O₃/Al laminated composites, nylon netwas introduced into the interfaces between Al₂O₃and Al layer, to fabricate Al₂O₃/Nylon/Allaminated composites. The thickness of adhesives layer is about o.15mm. The mechanicalproperties test show that, the fabricated composites, compared with Al₂O₃/Al laminatedcomposites, have lower density, modulus, bending strength and fracture toughness as well as aslight increase of fracture work. But the impact toughness is improved significantly.Furthermore, in order to improve the ductility of interlayer and the comprehensiveproperties of laminated composites, steel-epoxy interlayers was prepared by combined epoxy resin adhesives with60,80,120,150,200,250,300,350and400steel mesh, respectively.Then, Al₂O₃as ceramic layer, steel-epoxy as interlayers, Al₂O₃/steel-epoxy laminatedcomposites were fabricated via a simple moulding process at room temperature and5MPa.The results show that the laminated composites prepared using200steel mesh have the bestcomprehensive properties. As compared with Al₂O₃monolith, the fabricated composites havea closing bending strength of303MPa. Moreover, the fracture toughness, fracture work andimpact toughness of the composites are improved greatly, which is about14.5MPa·m^1/2,3.0KJ/m²and8.46KJ/m², respectively.In this thesis, the bridging effect for ductile interlayer of laminated composites wassimulated and the crack propagation patterns were analyzed and discussed. The results showthat the properties of ductile interlayer and the interface debonding have a significantinfluence on bridging stress and plastic deformation of interlayers. The results also show thatthere exist a critical value of metal layer thickness to ceramic layer thickness, namely （tm/tc）crit.When tm/tc＜（tm/tc）crit, the crack propagation tend to show macroscopic crack pattern. whereastm/tc＞（tm/tc）crit, the crack propagation tend to show multiple crack pattern.Finally, the water content, acid resistance and alkali resistance of the Al₂O₃/steel-epoxylaminated composites prepared using200steel mesh were tested. The results show that thewater content is low and the mass change treated in50%H2SO4and20%NaOH tend to befew due to the small area of resin exposed outside.Al₂O₃/Al, Al₂O₃/Nylon/Al and Al₂O₃/steel-epoxy laminated composites with typicalcharacteristics of ductile interlayers can be obtained in this research. Especially, theAl₂O₃/steel-epoxy laminated composites perpared using200steel mesh have the bestproperties. The laminated composites have low density, moderate strength, high fracturetoughness, high fracture work and impact toughness, good water resistance, corrosionresistance and high energy consumption during fracture, therefore have a good applicationprospect in fields where requiring energy absorbing such as in anti-impact applications.