Temperature Effect On The Mechanical Behavior Of Composite Sandwich Structure With Lattice Truss Cores

Carbon fiber composite sandwich structures with lattice truss cores possessbroad prospects for application in aeronautics and astronautics, because they can beultra-lightweight while also providing multifunctional characteristics. At present,the research on carbon fiber composite sandwich structures with lattice truss coresby domestic and foreign scholars mainly concentrates on room temperature. To thebest of our knowledge, no work has been done on the effect of temperature onmechanical behaviors of carbon fiber composite sandwich structures with latticetruss cores. Thus, it is necessary to investigate the mechanical behaviors ofcomposite sandwich structure with lattice truss cores subjected to a variation oftemperature to fill this information needed, which can aid the design and applicationof carbon fiber composite sandwich structure. The mechanical behaviors ofcomposite sandwich structures at high and low temperatures and after exposure tohigh temperatures were studied by experimental and theoretical methods in thisdissertation.The mechanical behaviors of carbon fiber composite sandwich structures withvertical lattice truss cores and pyramidal lattice truss cores at high and lowtemperatures were studied by experimental and theoretical methods. Thecompressive modulus and strength of composite struts and laminates at high andlow temperatures were measured experimentally, and they were fitted as functionsof temperature by theoretical model. The out-of-plane compressive stiffness andstrength of composite sandwich structures with vertical lattice truss cores andpyramidal lattice truss cores at different temperatures are derived theoretically, andthe comparison of the experimental data and predictions indicated that the stiffnessand strength of composite sandwich structure at different temperatures could bepredicted quite well by the derived formulae. At the same time, the in-planecompressive behaviors of composite sandwich structures with pyramidal latticetruss cores at high and low temperatures were investigated, and the effect oftemperature on in-plane compressive behaviors of composite sandwich structureswas obtained. Conclusions can provide data reserves and scientific basis for theapplication of composite sandwich structure with lattice truss cores at high and lowtemperatures.In order to study the effect of thermal exposure on failure mechanism of carbonfiber composite sandwich structure with pyramidal lattice truss cores, the out-of-plane compressive and shear behaviors of composite sandwich structures after high temperature exposure with different temperatures and time were investigated. Theout-of-plane compressive and shear properties of composite sandwich structure afterthermal exposure were measured experimentally, and the change law of out-of-planecompressive and shear properties with thermal exposure temperature and time wasgotten. Furthermore, analytical expressions were presented to predict the out-of-plane compressive and shear stiffness and strength of composite sandwich structureafter thermal exposure. The effects of thermal exposure on failure mechanism ofcomposite sandwich structures under out-of-plane compressive and shear loadinghave been revealed. The node failure was observed for the specimens exposed totemperature in a range of20～250℃under out-of-plane compressive and shearloading. However, the delamination and buckling failure were observed under out-of-plane compressive loading when the exposure temperatures are higher than250℃, and face sheet delamination and node failure were observed under shear loading.At the same time, the failure mechanism of composite sandwich structure at hightemperature was compared with the failure mechanism after high temperatureexposure. The results showed that the failure mechanism of composite sandwichstructure at high temperature was different from the failure mechanism after hightemperature exposure.The in-plane compressive and bending behaviors of composite sandwichstructures with pyramidal lattice truss cores after thermal exposure were studied.The changes of in-plane compressive and bending behaviors after thermal exposurewere analyzed, and the interfacial microstructure was also examined by scanningelectron microscope (SEM) in order to investigate the effect of thermal exposure onfailure mechanism. The change law of failure load of composite sandwich structuresunder in-plane compression and three point bending with thermal exposuretemperature and time was obtained. The decrease in the failure load is attributed tothe degradation of the matrix properties and the degradation of fiber-matrixinterface properties, which seriously weakened the bearing capacity of overallstructure. The analytical expressions for failure load of composite sandwichstructures under in-plane compression and three point bending were derived, and thefailure load of composite sandwich structure after thermal exposure was predictedwith proposed method and compared with measured results.The low velocity impact behavior of composite sandwich structures withpyramidal lattice truss cores after thermal exposure was investigated byexperimental methods. The effect of thermal exposure temperature and impactenergy on the low velocity impact response of composite sandwich structure wasobtained, and the failure mechanism and absorbed energy characteristics of composite sandwich structure after thermal exposure were revealed. Furthermore,the residual compressive strength after impact was studied by experiment, and theresidual bearing capacity after impact was analyzed. Our results showed that theresidual compressive strength were significantly dependent on the thermal exposuretemperature and impact energy.