Buckling Analysis And Stacking Sequence Optimization Of Composite Laminated Structure

Composite materials have many advantages,such as high specific strength,high specific stiffness,strong in design and so on.It has been applied more and more widely in aerospace,bridge engineering and other fields.For composite laminates,when they are subjected to compression load,the failure mode is usually buckling.And after buckling,it still has great bearing capacity,namely post buckling strength.Therefore,in order to improve the efficiency and bearing capacity of composite laminates and ensure the safety of the structure,the buckling and post buckling behavior of laminate structure and the optimization method of stacking sequence are studied in this paper.The main contents are as follows:(1)The buckling analysis model of composite laminated plates is established,and eigenvalue buckling and nonlinear finite element buckling analysis are carried out.In addition,the progressive damage analysis method is introduced to predict the ultimate strength,damage form and expansion process accurately.The Hashin criterion is used as the failure criterion of the laminate.The progressive damage analysis is realized by establishing the Camanho stiffness degradation model and writing the USDFLD user field variable subroutine.Through the analysis of the stability of laminates,the critical load and the buckling mode are calculated,and the validity of the finite element model is verified by comparing with the theoretical solution of the buckling load of a simply supported rectangular laminated plate.The effects of boundary conditions and stiffness degradation on post buckling analysis are further studied.(2)In order to improve the buckling load and ultimate strength of laminated plates,the stiffeners were added to the laminates model,and buckling and post buckling analysis of stiffened plates were carried out.Considering the debonding failure,the interface between skins and stiffeners is simulated by Cohesive interface element.It is found that the post buckling bearing capacity and failure process of stiffened plates can be more truly simulated by introducing the stiffness degradation model and using the Cohesive element to consider the debonding.For the square plates of a/b=1,matrix tensile failure occurs mostly in four corners and the middle of the stiffeners.The height of the stiffener will change the buckling mode and the final instability form.The increase of the stiffener height in a certain range can increase the buckling load and ultimate strength,and the increase of stiffener height is more significant to the ultimate strength.(3)In order to improve buckling load,this paper is based on the genetic algorithm and the random normal distribution optimization algorithm,taking the buckling load of the axial compression composite laminates as the objective function,the optimal design of the stacking sequence is carried out.Two optimization algorithms are programmed in MATLAB language to optimize the layer sequence of symmetrical balanced laminates with different layers and boundary conditions.The results show that the genetic algorithm with integer coding and penalty function can be used to optimize the sequence of laminated plate;the results of random normal distribution optimization algorithm are consistent with the results of the genetic algorithm,and the buckling load of the optimized layer is obviously improved;the random normal distribution optimization algorithm is more concise and practical and easy to converge,which is more suitable for engineering application of stacking sequence optimization design of laminated plates.