Thermal And Mechanical Properties Of Multifunctional Composite Honeycomb Sandwich Structure

Heat dissipation is increasingly important at high-density electronics,communication satellite,and advanced spacecraft,due to the continuing miniaturization and high-density integration of electronic device components where the thermal load is even expected to reach 10,000 kW.The harsh thermal load will affect the reliability of spacecraft,and limit its service life.Therefore,modern satellite structures require multifunctionality including not only mechanical but also thermal performance.In this dissertation,we successively research into the design,fabrication,thermal and mechanical properties of carbon fiber reinforced polymer(CFRP)composite laminates with high thermal conductivity,multifunctional composite honeycomb sandwich structure,hierarchical composite honeycomb structure as well as graphite foam hierarchical composite honeycomb structure.This paper focus on utilizing a simple method that assembling graphite films with high thermal conductivity(TGS)and low-cost CFRP to create a TGS reinforced CFRP(CFRP/TGS)composite laminates,and its high thermal conductivity,thermal expansivity and mechanical property are studied.The measurement results show that TGS improves the in-plane thermal conductivity of hybrid CFRP/TGS composite laminates to that of aluminum alloy,simultaneously,CFRP/TGS possess the good mechanical property and low thermal expansion coeffictent of CFRP.Moreover,this paper developed an effective method of constructing a 3D thermal conductive pathway to improve the through-thickness thermal conductivity of CFRP composite laminates.Then,a z-filler laminated composite panel is fabricated by filling the copper rods and coating the aluminum foils,and its effective thermal conductivity is investigated,both experimentally and theoretically.The through-thickness thermal conductivity of z-filler composite laminates has been significantly improved by increasing the z-filler volume fraction.However,it is inefficient to place the copper rods into the holes one by one during manufacture process.Whereas because the copper spheres are easy to roll into the holes,which will greatly simplify the manufacture process,the copper rods are replaced by copper spheres.The new manufacture process decreases the interface thermal resistance,and further improves the through-thickness thermal conductivity of z-filler composite laminates.Except for the demand of high thermal conductivity for CFRP,multifunctional requirements are also proposed for the light sandwich structures.In this paper,a multifunctional composite square honeycomb sandwich structure(MCHSS)is developed which provides both high thermal conductivity and adequate mechanical property for a thermal management system.The out-of-plane thermal conductivity of MCHSS is improved by TGS,and investigated both theoretically and experimentally.There are two most efficient methods to further enhance the out-ofplane thermal conductivity of MCHSS: one is to increase the TGS volume content,and the other,to decrease the interface thermal resistance.Results i ndicate that,except for high specific thermal conductivity for thermal management,MCHSS also possess adequate mechanical properties for structural applications.Thus,MCHSS can be considered as a promising candidate for multifunctional structure material in the high-end heat dissipation field.This paper fabricates hierarchical composite square honeycomb structures(HCSHS)by a simple “snap-fit” assembly method.The mechanical responses of HCSHS under compression and shear have been experimentally invest igated,and their compressive and shear strengths characterized as a function of core density,and compared with micromechanical predictions.The results reveal that it is feasible to further improve compressive strengths by selecting the suitable polymethacrylimide(PMI)foam and its optimal thickness.Moreover,hierarchical structures increase the core-to-facesheet adhesive strength due to its large bonding area,and thus possess higher shear strengths.The above work applies the design ideas of hybrid materials and hierarchical structure,which improves the thermal conductivity and mechanical properties,respectively.However,the low thermal conductivity of PMI foam will do nothing to improve the thermal conductivity of HCSHS.Hence,this paper fabricates hierarchical composite honeycomb structures by replacing PMI foam with graphite foam to improve both the mechanical properties and the thermal conductivity,and its thermal conductivity is measured.Results shows thermal conductivities of hierarchical composite graphite foam honeycomb structures are high and increase with the thermal conductivity of graphite foam and facesheets.