The Design Technology Research On The Structural-functional Integration Air Inlet Manufactured By Fiber Placement

Compared with the metallic air inlet used in China,the composite automated fibre placed one can improve the integrity and sealing property significantly.It is able to meet the design requirements of high efficiency and light weight,and more suitable to withstand the complex load conditions such as charging pressure,oil pressure,hammer shock and noise in the inlet.At the same time,in order to reduce the electromagnetic defects of the inlet surface,the application of the radar absorbing structure can not only improve the integrity,but also the risk of the radar absorbing materials falling from the inlet surface can be eliminated.As a result,the stealth performance,safety and durability of the aircraft can be further promoted.For the micro-level of the fiber-placed composite structure,a theoretical method and a structural strength analysis method are proposed as well as the analysis method considering the defects of the fiber spreading process was established.Based on the traditional analytical method of laminated composite,a numerical analysis method for buckling and post-buckling of negative curvature grid stiffened structures is established to analyze its progress of buckling,post-buckling and failure under typical normal load of inlet.The in-plane damage of composite skin and stiffeners is simulated using the modified Hashin criteria,which provides the longitudinal and transverse failure of the material.Besides,the tensile and shear failure criteria are adopted for the interface between the skin and the stiffeners.The failure caused by normal and tangential loads provides the basis for the optimal design of the parameters of the negative curvature reinforced structure.A kind of composite cross joint was raised.Besides the vertical and horizontal reinforcement butt joint simulation analysis method is proposed and applied to study its failure mechanism.Thus the best suitable form of cross joint for meeting the normal load-bearing demands is found easily.The process and method of the design and analysis of the fiber placement process/structure integration was raised.The typical process parameters of fiber-placed which affect the manufacturing quality of the fiber-placed structure are investigated deeply.Besides the recommended process parameters for the manufacturing of profiled fiber-placed air inlet are given.A digital definition method of fiber-placed track suitable for the profiled fiber-placed air inlet with the complex geometry was developed based on the method of fiber-placed track with fixed Angle.Experimental results show that this method can meet the requirements of the profiled fiber-placed composite air inlet structure.Through the simple synthesis method,using loofah flesh as raw material,the microwave absorbing materials with light weight,low cost and wide absorbing band are prepared,which exactly solve the problem of debonding and maintenance of traditional coated absorbing materials.The mechanism of the microscopic pore structure including material mechanical properties,heat transfer and electromagnetic performance was proposed based on the model of material anisotropy microstructure characteristics.Using graphene/porous carbon absorbing material as raw material based on aramid paper honeycomb,the new type of stealthy structure filled with graphene honeycomb sandwich of carbon/graphene composite sponge was prepared,which was provided with the horizontal ordering arrangement of graphene/porous carbon absorbing material layers by temperature control in the macro and micro two scales as well as in the horizontal and vertical directions,respectively.The test show that the sponge has excellent electromagnetic shielding effect.A new type of stealthy structure filled with graphene honeycomb sandwich is studied to realize the stealthy requirement of the whole inlet of composite material.And the electromagnetic and mechanical properties of the stealthy structure based on load bearing and stealthy integration are established.Based on the above research results,the manufacturing technology plan of structure and stealth integrated structure is formulated,and the whole inlet of composite structure with stealthy functional layer is produced,which lays a solid foundation for the development of stealthy inlet with integrated structure and function.The air inlet test pieces’ design simulates the load condition and the relationship with the surrounding structures.Considering requirements of weight,assembly,stealth and so on,the medium thickness skin,the fewer-stiffener-structure are selected.The vertical and horizontal reinforcement butt joint simulation analysis method is applied to compare the different reinforced layouts.According to the characteristics of fiber placement,the inlet skin uses 0°,±45°,90°equilibrium layer,and the long stringers and frame caps are laid with symmetrical equilibrium layers.For domestic current fiber and resin series,high-strength skin is fabricated from wet state.Then it is co-cured with the stiffeners.The performance test,equivalent stiffness model test,typical part test,special-shaped part test and stealth test are mainly carried out in the verification of inlet design and analysis.A test method considering the impact characteristics of hammer shock wave was proposed and the simulation test of hammer shock wave on the inlet wall was carried out.The problem that the results of design tending conservative because of the effect of hammer shock wave load is not considered in the traditional static test of composite wall is improved.According to the analysis of the test data,the prediction and test results of the equivalent stiffness model are basically the same,which can meet the engineering needs.The hammer shock test method can accurately verify the ability of the wall to bear the impact load.The fiber-placed inlet test pieces can withstand 100% design load,and meet the ideal functional requirements of the stealth reduction coefficient.The design and analysis method suitable for the structural-functional integration Air Inlet manufactured by Fiber Placement was put forward for the first time and its engineering application was successfully achieved.Through the design,analysis and test of the fiber-placed air inlet,the feasibility of the method for the analysis of the equivalent stiffness and structural strength of the fiber-placed composite is verified.Meanwhile,the material system,the curing molding process and the structural design method suitable for the fiber-placed air inlet process are determined.It is of high practical value to improve the stealth performance of the aircraft and effectively reduce the weight of the structure.