Preparation And Mechanical Properties Of Fiber Column Reinforced Composite Sandwich Structures

At present, sandwich structures are widely used in aerospace, shipping and high speed traffic engineering field, because of their rational structure, larger specific stiffness, higher specific strength and the designable characteristic. They are usually composed of two thin facehseets with high strength and high modulus and thick lightweight core. The core and the facesheets are usually connected by welding or adhesive in the traditional sandwich structures. This will increase manufacturing costs and bring the problem of weak interface. In order to solve the problem of weak facesheets-core interfaces and fabricate sandwich structures of high performance, composite columns reinforced foam core sandwich structures and all composite lattice truss core sandwich structures were designed and manufactured in one process. And mechanical properties of these new sandwich structures were investigated by tests and theoretical analysis.The technologies of Z-direction reinforced foam core sandwich structures, the preparation process and mechanical properties of lattice truss core sandwich structures are reviewed in Chapter one. In addition, the background, significance and topics of the present project are demonstrated in this chapter.In chapter two, the composite columns reinforced foam core sandwich panels were fabricated by Vacuum Assistant Resin transfer molding (VARTM) technology. The mechanical properties of sandwich structures with five different volume fractions of composite columns were investigated under compressive, three-point bending and shear load. The results show that, the mechanical properties could be improved by introducing the composite columns, especially, make up the lack of shear and compressive properties because of the lower strength and stiffness of the foam core. So that improves the bending properties of the foam core sandwich structure.The introduction of composite columns can increase the mechanical properties of foam core sandwich structure, but it is not clear how it affect. In Chapter three, the micro-mechanics modeling of composite columns reinforced foam core sandwich structure was established, the normal Young's modulus and transverse shear modulus of the composite columns reinforced foam core were predicted by using corrected Mori-Tanaka method. The volume fractions and diameter of the composite columns which affect the stiffness of sandwich core are demonstrated.The load is carried by the composite columns of the sandwich structures, and the foam core is used to locate the composite columns. If we remove the foam in the sandwich structures, that will not reduce the mechanical properties of the sandwich structures and there will be large space in the core which can be used as multifunctional structure. The composite columns reinforced foam core sandwich structures whose foam core was removed are lattice truss core sandwich structures. The lattice truss core sandwich structures are the research focus in mechanics and material field. But now the researches of lattice truss core sandwich structure are focused on the sandwich structures made from metal materials. Compare to the metal materials, composite materials are lower density,higher specific strength, higher specific stiffness and designable characteristic. So research of lattice truss core sandwich structures made of composite materials has a greater application value and scientific significance. In Chapter four, vertical, inclined and pyramidal lattice truss core sandwich structures are designed and manufactured by prepreg lay-up process.The typical failure modes are observed under compressive, shear and in-plane compressive load. The buckling and splitting of truss members were observed in compressive and shear test. The buckling of sandwich structure, wrinkling and delamination of facesheets were observed in in-plane compressive test. And no nodal failure is observed. The strain was calculated by mechanics of materials method and the the geometry of the unit cell when the normal stress and shear stress was applied on the unit cell of the lattice truss core. The compressive Young's modulus, shear modulus of composite lattice truss core sandwich structures were calculated by the ratio of stress and strain. The compressive strength was obtained while the truss members were buckling and splitting of composite lattice truss core sandwich.Compared to the tradition sandwich core, the new type composite cores are lower density, higher specific strength,higher specific stiffness and designable characteristic. They could be used as main loaded structures in aerospace and high speed traffic engineering field, and may be used as multifunctional structures because of large space between the lattice truss cores.