Investigation On Design Method For Bending-twisting Coupled Structure With Asymmetric Composite Laminates

Bending-twisting coupled structures have wide uses in many kinds of structures,for example,wind turbine blades and wings of aeroplane.Focusing on the deficiencies of bending-twisting coupled structures with symmetric laminates,such as heavy weight and complex couplings,the design method for bending-twisting coupled structure using asymmetric laminates is studied in this dissertation.The design schemes for bending-twisting coupled structure using three kinds of asymmetric laminates with single coupling are proposed.The main works are summarized as follows:The mechanical characteristics of asymmetric laminates are analyzed.1)The mechanical characteristics,such as the constitutive equations,mechanical couplings,hygro-thermal deformation and bucking strength,are analyzed.2)The approach of robustness analysis for the mechanical characteristics of asymmetric laminates is proposed using Monte Carlo method.The design sche me for bending-twisting coupled structures using extension-shear coupled laminates with immunity to hygro-thermal shearing distortion is proposed.The concept of asymmetric laminates with immunity to hygro-thermal shearing distortion is proposed.Material-independent necessary and sufficient conditions are derived for extension-shear coupled laminates with immunity to hygro-thermal shearing distortion.An optimization is performed to identify extension-shear coupled laminates with immunity to hygro-thermal shearing distortion that produce maximum extension-shear coupling.The coupling and hygro-thermal stablity of extension-shear coupled laminates with immunity to hygro-thermal shearing distortion are validated using numerical simulation method.The sensitivity analysis is performed to demonstrate the robustness for cured shearing distortion and warping distortion of extension-shear coupled laminates with immunity to hygro-thermal shearing distortion to small errors in ply orientation using analytic method.The design scheme for bending-twisting coupled structures using extension-shear coupled laminates with immunity to hygro-thermal shearing distortion is proposed.The analytic expression for twist deformation of bending-twisting coupled structure using extension-shear coupled laminates with immunity to hygro-thermal shearing distortion is derived.The design scheme is validated using numerical simulation method.The design sche me for bending-twisting coupled structures using hygro-the rmal curvature stable(HTCS)laminates with extension-twisting coupling is proposed.Material-independent necessary and sufficient conditions are derived for HTCS laminates with extension-twisting coupling.The HTCS laminates with extension-twisting coupling can be derived by applying off-axis alignment to standard forms of HTCS laminates.HTCS laminates with extension-twisting coupling are designed to obtain optimal extension-twisting coupling and buckling strength.The coupling and hygro-thermal stablity of HTCS laminates with extension-twisting coupling are validated using numerical simulation method.The bucking strength of HTCS laminates with extension-twisting coupling is analyzed.The sensitivity analysis is performed to demonstrate the robustness for cured warping distortion of HTCS laminates with extension-twisting coupling to small errors in ply orientation using analytic method.The design scheme for bending-twisting coupled structure using HTCS laminates with extension-twisting coupling is proposed.The design scheme is validated using numerical simulation method.The design scheme for bending-twisting coupled structures using HTCS hybrid laminates with extension-twisting coupling is proposed.The analytic expressions of the stiffness coefficients,the thermal stress resultants and thermal moments are derived using the laminate parameters for hybrid laminates.The simplized analysis model for hybrid laminates is established.Based on the simplized analysis model,a survey is performed to identify free form of HTCS hybrid laminates with extension-twisting coupling that produce maximum extension-twsiting coupling through a constrained optimization routine.The coupling and hygro-thermal stablity of HTCS hybrid laminates with extension-twisting coupling are validated using numerical simulation method.The sensitivity analysis is performed to demonstrate the robustness for cured warping distortion of HTCS hybrid laminates with extension-twisting coupling to small errors in ply orientation using analytic method.The design scheme for bending-twisting coupled structure using HTCS hybrid laminates with extension-twisting coupling is proposed.The design scheme is validated using numerical simulation method.Optical measure ments for different kinds of couplings of asymmetric composite structures are performed.The experimental schemes for measuring extension-shear coupling,extension-twisting coupling and bend-twisting coupling are designed.Optical measurements for extension-shear coupling,extension-twisting coupling and bend-twisting coupling are performed to verify the design methods of bend-twist coupled structures using asymmetric composite laminates.In conclusion,the bending-twisting coupled structures are designed using different kinds of asymmetric composite to overcome defects of the bending-twisting coupled structures with symmetric composite.The present work provides a technical support for the design of adaptive structures,such as wind turbine blades and wings of aeroplane,which is of great value in engineering applications.Moreover,the theoretical and methodological systems about the design of bending-twisting coupled structures using asymmetric composite are formed in this dissertation,which are of great value in theory.