Study On Stacking Sequence Optimization Of C Omposite Laminates Con Sidering In-situ Effect

Fiber-reinforced composite materials are widely used in the aerospace field due to their light weight,high specific stiffness and large specific modulus.Aircraft structural design should maximize the potential of the structure while meeting the strength requirements.With the increasing use of composite structures as primary or secondary bearing structures,optimization of composite materials has become the focus of research.Stacking sequence optimization of laminates is one of the research directions.The mechanical properties of the plies in the composite multi-directional laminates are different from those in the unidirectional laminates and show obvious in-situ characteristics.If the in-situ effect is taken into account in the process of optimization,the optimization result will be more reasonable However,the current research mainly focuses on the failure prediction of laminates considering in-situ strength,and has not considered the optimal design in terms of in-situ effects.Two kinds of stacking sequence laminates with three different open-hole sizes were studied by using the finite element progressive damage analysis considering in-situ effect.It is concluded that the finite element strength analysis considering the in-situ effect has higher prediction accuracy than the finite element strength analysis without the in-situ effect.A genetic algorithm considering the in-situ effect was proposed to optimize stacking sequence of composite laminates.Design variables are stacking sequence of the laminate and strength ratio as its fitness function,some constraints were also considered according to real situations.Firstly,Optimization using genetic algorithm was performed.After improving the shortcomings of the genetic algorithm,the improved adaptive genetic algorithm was realized.This method improves the optimization efficiency and the ability of finding the global optimal solution.Finally,a genetic algorithm stacking sequence optimization considering the in-situ effect was realized based on the previous works.Optimal analysis of laminate under unidirectional load and multi-directional loads at different load ratios were carried out to analyze the lawsThe following conclusions were obtained:Prediction accuracy was improved by using finite element strength analysis considering in-situ effect.The fitness value obtained by optimization using the genetic algorithm that considers in-situ effects was higher than the fitness value obtained by optimization using the genetic algorithm that does not consider in-situ effects.Under axial load or under axial and transverse bidirectional load,The final stacking sequence of laminates obtained by genetic algorithms without considering the in-situ effect were not all the same,but The stacking sequence of laminates obtained by using genetic algorithm considering in-situ effects were all the same,stacking sequence is[0/90/0/90/0]s.According to the in-situ strength formula,such a layup sequence can ensure that the transverse tensile strength and shear strength of the plies are kept at a maximum;Compared with the fitness value optimized by the adaptive improved genetic algorithm without considering the in-situ effect of the laminate,on the basis of considering the in-situ effect of the laminate,the adaptive improved genetic algorithm was applied to optimize the laminate under unidirectional and bidirectional load,the fitness value obtained under unidirectional load was higher than that obtained under bidirectional load;Under bidirectional load,the change of axial load Nx has a greater impact on the optimization results,increase the loads can make the fitness values obtained by the two algorithms more closer,thus narrowing the prediction gap between the two algorithms.