Bending, Buckling And Vibration Properties Of Composite Lattice Sandwich Strucutres

Lattice sandwich structure, as a novel kind of multifunctional lightweightstructure, has widely potential application in the fields of astronautics, aeronautics,ship-building and transportation. They have been traditionally made of metallicmaterials such as aluminium alloy or304stainless steel. There are many advantagesof carbon fiber reinforced composite materials over traditional metallic materials,such as low density, high strength, and high modulus. Therefore, composite latticesandwich structures have been paid more attention in recent years. Due to somefeatures of composite lattice sandwich structures, such as high porosity, periodicity,and anisotropy, their stiffness, strength, stability and vibration properties will shownew characteristics. However, there is little research in this area. In this dissertation,three-point bending problem, global buckling problem, and free vibration problemof composite lattice truss core sandwich structures are studied by the methods oftheoretical prediction, numerical simulation and experimental measurement. Themain contents are as follows:The stiffness and strength behaviors of composite lattice truss core sandwichstructure under three-point bending load are investigated firstly. Converted discretelattice truss core to continuum homogenized material, the expression for thedeflection is derived by considering bending of the face sheets and transverseshearing of the core. The stress states within the face sheets and the truss membersare analyzed respectively by taking the lattice truss core sandwich structure as acomposite structure composed of multi-span thin plates and one-dimensional strutelements, and the critical loads for various failure modes are predicted. Collapsemechanism map is constructed on that basis, and the relations between failuremodes and structural geometric dimensions are revealed. Optimized design ofcomposite lattice truss core sandwich structure is carried out with the goal of load-carrying efficiency maximization. The advantage of this new type of lightweightstructure is reported by comparing the performances of composite lattice sandwichstructure, metallic lattice sandwich structure and composite laminates.Secondly, the global buckling problem of composite lattice truss coresandwich structure under in-plane compressive load is investigated. On the basis ofAllen’s displacement model (which assumes that the face sheets and the core havedifferent rotation angles, and the rotation angle of the core is a function of thetransverse displacement of the sandwich structure), considering a sandwichstructure with laminated face sheets, the expression of general solution for transverse displacement is derived using the energy-variational method, theunknown coefficients in the general solution are determined by the correspondingboundary conditions, and the buckling modes as well as critical buckling loadsunder various typical boundary conditions are calculated. The errors of both Eulertheory and Timoshenko theory increase with the shortening of the buckling lengthof the sandwich structure, while the present method overcomes this problem.Then, the free vibration problem of composite lattice truss core sandwichstructure is studied by theoretical and numerical methods. An improved zig-zagmodel, which is suitable for free vibration problem of sandwich structure not onlyunder simply-supported boundary conditions, but also under other boundaryconditions, is constructed on the basis of Allen’s model, and the natural frequenciesand corresponding vibration modes of sandwich structure under various boundaryconditions are calculated. Besides, a finite element model is set up to simulate thefree vibration characteristics of lattice truss core sandwich structure, and the effectsof material properties and geometric parameters on the natural frequencies of latticetruss core sandwich structure are also discussed.Finally, the effects of local damage of the core on the vibration characteristicsof composite lattice truss core sandwich structure are studied by experimentalmodal analysis and numerical simulation method, and the effects of damage extents,damage locations, damage forms, and boundary conditions on the naturalfrequencies and natural vibration modes of lattice truss core sandwich structures areinvestigated. It is found that local damage will decrease the natural frequencies andresult in obvious local deformations appearing in the natural vibration modes. Thepresent study provides useful guidance for engineering application of compositelattice truss core sandwich structure.