Active Heat Transfer And Optimization Design For Multi-functional Composite Sandwich Structure With Lattice Truss Cores

The interest for miniaturization, integration and lightweight multi-function has rapidly grown in various fields over the last decade, especially in areospace field with strong desires of weight loss, volume constraint and multifunctional integration. The stretching-dominated lattice topology structures are regarded as the functional configuration material with careful consideration of material, structure and function, which have not only excellent mechanical properties but also the potential advantages of realizing the multifunction integration of heat dissipation, energy absorption, impact resistance and so on. Carbon fiber reinforced composite lattice truss core sandwich structure (CLTCSS) is considered as the most promising new generation ultralight material candidate. It greatly caters to the development requirement of multi-functional composite structure.In this dissertation, multifunctional electronic structure of spacecraft subsystems is considered as the engineering application background, and the aim is to realize the functional integration of load bearing and thermal control. The studies on the preparation technology, mechanical properties, active thermal control performance and multi-field coupling behavior of CLTCSS have been gradually carried out. Moreover, the multi-objective optimization to the core geometry parameters of structure has also been presented. All the above can lay the solid foundation for the achievement of structural multi-functional integration.Based on the deficiencies of available preparation technology, the carbon fiber composite pyramidal truss core sandwich structure with cross-bars is fabricated by a hot-press molding method in two steps. A series of analytical and experimental studies are carried out under the out-of-plane compression, in-plane shear in-plane compression and three-point bending. Results indicate that the structural mechanical properties are improved, but the node rupture is still a key issue to restrict the full release of potential ability. Moreover, an interlacing laminate form of the core-nodes is presented to overcome the new failure mode of core-separation from cross-bars. Compared with the same kind structure and the Ashby material, the improved structure shows excellent comprehensive mechancial performance, especially in the low density region, and much space still remain for further improvement.Theoretical thermal field analysis of CLTCSS with a localized internal heat sources under forced-water convection is conducted based on the thermal resistance network model and classical fin theory. The fluid flow and heat transfer are numerically studied over a wide range of Reynolds number. The heat transfer mechanism is revealed based on the local flow pattern and velocity field characterization, and the heat transfer performance is characterized in terms of the non-demensional parameters of heat transfer and thermal field distribution. Moreover, as a main measurement index of thermal control, the responses of maximum temperature of heat source on main thermal control factor are discussed, and the fitting prediction function and velocity threshold is shown，respectively. Compared with other heat dissipation media, the CLTCSS shows good comprehensive heat transfer performance.The structural responses of CLTCSS with a localized internal heat sources subjected to forced water convection and typical flexural load are numerically studied. Combining actual condition, the complex muti-field coupling problem is simplified into the simple combination problems. The temperature and stress field are analyzed under the thermo-hydro-mechanical multi-feild, revealing the difference of the field distribution between sequentially thermo-mechanical coupling results and fully coupling ones. Simultaneously, the effects of the structural deformation on the local fluid-flow and heat transfer performance of the structure are explored. Results indicate that the concave deformation with respect to heat source has a positive effect on the improvement of heat transfer performance.To achieve the functional integration of load bearing and thermal control, the selective combination problems constructed based on relative density, mechanical properties and thermal control maximum temperature of CLTCSS are considered to optimiz the main core-geometry parameters of core-strut inclination angle, core height and core-strut diameter by the Pareto multi-objective genetic optimization algorithm. The corresponding Pareto front and Pareto chat are employed to explore the global sensitivities of optimization problems to sub-objective functions and the single sensitivities of sub-objective functions to optimization variables, giving the fitting relationships of temperature and relative modulus as a function of relative density. Results show that the core height is the dominate parameters, and the optimal core-strut inclination angle is about45degree. The Pareto optimal solutions can provide the alternatives and guidance to engineering design, which should take specific demands, preparation technology and cost into account.