High Stiffness And High Strength Design Of Composite Wing Spar

As a new energy aircraft with high altitude & long-endurance and its potential application for communications relay,meteorological monitoring,disaster monitoring,navigation and reconnaissance,near-space solar unmanned aircraft has become a hot research topic in the aerospace field.For complicated loading conditions and energy saving purposes,high stiffness & strength and light weight spar are required by the wing structure.To fully utilizing the advantages of truss structure with high stiffness and thin-ply laminates with high strength,a light weight wing spar design with thin-ply laminated composite truss structure was proposed in this paper.Firstly,loading efficiency of the composite wing spar with different configurations(I-beam,box-beam,pipe-beam and truss structure-beam)was compared and the one with highest loading efficiency was identified.Multi-parameters optimization was conducted and the optimum design was experimentally demonstrated.Then,the strength of thin-ply laminates was experimentally,numerically and theoretically analyzed.Acoustic emission technology was also employed to investigate the failure mechanism.Finally,thin-ply laminates was applied to design and manufacture the composite pipe which is adopted as composite truss pipe element.The mechanical performance of the pipe was evaluated.The details of main work includes:Isight was employed to integrate ANSYS to optimize the geometric configuration and dimensions of composite truss spar.The results show that,the truss wing spar has the highest bearing efficiency compared with I-beam,box-beam and pipe-beam.The composite truss with square cross section was fabricated and the vibration characteristics were tested by hammering method.The vibration modes and frequency were obtained and that fit the finite element analysis results good.In order to identify the acoustic emission signal characteristics with different damage and failure modes,test samples of pure resin casting matrix,resin casting matrix with a fiber tow,and laminates with prefabricated delamination flow were prepared.The peak frequency of acoustic emission signals corresponding to matrix damage and fracture,delamination or interface debonding and fiber breakage were obtained.Unidirectional,cross-ply and quasi-isotropic laminates were prepared by T300 carbon fiber/epoxy thin prepreg with different thickness and the mechanical performance of these samples were tested.The results show that,comparing with laminates with standard ply thickness 0.125 mm(T-125),the laminates with ply thickness 0.055 mm(T-55)and 0.020 mm(T-20)have higher unidirectional tensile strength and short-beam shear strength.The results of open-hole tensile test show that,thin-ply laminates have higher initial damage strength(damage resistance)but lower ultimate tensile strength.Axial compression properties were tested for composite tubes with different ply thickness.The results show that,the decreasing of ply thickness is beneficial to increase the axial compression buckling load.Compared with T-125 tube,the axial compression buckling load of T-20 and T-55 cross-ply laminated tube increase by 53.69 % and 16.63 % respectively,and the axial compression buckling load of T-20 and T-55 quasi-isotropic laminated tube increase by 12.59 % and 9.68 % respectively.The theoretical calculation showed that the change of axial bending stiffness was the main factor to the increase of the compressive axial buckling load while decreasing the ply thickness.In addition,the homogenization distribution of interlaminar shear stress in the composite thin-walled tube increased its resistance to local buckling.The pipe employed as composite truss wing spar were furtherly designed by using T-55 thin layer.The results of the pipe bending test show that,the T-55 tube and T-125 tube have almost the same bending stiffness,but the ultimate bending load of T-55 tube is 26.89 % higher than the T-125 tube.Both the results of acoustic emission detection and finite element progressive damage simulation show that the thin-ply pipe has higher damage tolerance and less damage area.