Design And Research Of Variable-stiffness Composite Structures Based On Curve Placement Mode

Compared with traditional composite materials,variable stiffness composite materials can achieved designability of composites better and improve fiber strength utilization.Currently,fiber angles of variable stiffness composite predominantly linear vary,there are problems that plies of composite laminates,laying paths and fiber orientation angle variation curves were rarely optimized.This paper designed several kinds of fiber placement angle variation curves,focused on researching the affect of each fiber angle variable curve of variable stiffness composite on the buckling behavior,mainly to do the following work:Firstly,stiffness and buckling formulas of composite laminates were used to calculate the influence of laying angle and aspect ratio of constant stiffness laminates on the axial compression buckling loads,shear buckling loads,buckling half wave number.Buckling loads of laminates were calculated under four kinds of boundary conditions through finite element software ANSYS,rationality of the finite element model was confirmed;four fiber placement angle variation curves were designed,and the fiber angle relationships were established.The corresponding curvilinear fiber placement trajectory equations were derived.Buckling loads of variable stiffness composite laminates with linear angle variation and nonlinear fiber angle variation were calculated,and compared to constant stiffness composite baseline laminate[45/0/-45/90]_s.Finally,the advantages and disadvantages of embedded ANSYS optimization algorithm and outside MATLAB genetic algorithm were described.We optimized fiber angle of constant stiffness laminates and plies of variable-stiffness composite laminates with both linear angle variation and nonlinear fiber angle variation.In order to prove optimal results,this paper used progressive failure to calculate both the constant stiffness laminates and optimal variable stiffness composite laminates,drawing the following conclusions:?1?Based on axial compression buckling load,this paper used the finite element method to optimize fiber angle?of constant stiffness laminate[±?]_2s under the conditions:·four sides simply supported;·two long sides clamped and two short sides simply supported;·three sides simply supported and a long side free;·two short edges simply supported with one long side clamped and the other long side free.The best fiber angles?were about 45,45,20 and 48 degrees.The results were consistent with optimal fiber laying angles calculated by theoretical method.?2?Under the other three kinds of boundary conditions?excepting those where the two long sides were clamped and the two short sides simply supported?,this paper compared critical buckling load of the best composite laminates with both linear angle variation and nonlinear fiber angle variation to optimal straight fiber laminates under the same constraints.The trends of improvement were same,and the orders of improvement were as follows:Lower parabola curve>Sinusoidal curve>Linear curve>Upper parabola curve.?3?Under the boundary conditions where trilateral sides simply supported and a long side free,buckling loads increase most obviously.The buckling load of laminates constructed of optimal plies with the best variable curve fiber placement angle?under the parabola?increased by 39.8 percent compared with optimal straight fiber laminates.The method of designing,optimizating,evaluating and verifing placement angle of variable stiffness composite materials has a certain practical significance for theoretical development and engineering applications of designing a variable stiffness composite structure;improving structural strength,savingmaterials and advancing fiber placement technology.