Variable Stiffness Placement Optimizes The Mechanical Properties Of Composites

Carbon fiber composite material is a kind of new materials,with high strength,rigidity and can be designed,which has a series of advantages.In recent years,carbon fiber composite material is increasing widely used in the aviation,machinery,medicine and other fields.However,in practical engineering applications,it is often necessary to perforate the composite laminates,when the component is subjected to load,it is easy to produce stress concentration around the hole.Due to the presence of such phenomenon,the bearing capacity of laminated component decreases and easy to be unstable.Therefore,how to reduce the stress concentration around the hole and improve the bearing capacity of the laminates,which have been studied by many scholars.In this paper,we design the variable stiffness placement trajectories of composite laminates,which based on the potential flow field function.we provide a new effective solution for improving the mechanical properties of the laminates.The placement trajectories of composite laminates are constructed by the potential flow field function,which establish bridge between the design of the placement trajectories and the mechanical analysis.Laminates have different laying angles at different locations based on the curve placement trajectories,the target which designs stiffness at the fixed-point is achieved.Designability characteristics and bearing capacity of carbon fiber can be fully utilized,while overcoming the shortcomings that traditional linear placement laminates only have invariable stiffness and easy to be unstable.Fast and effective LM algorithm is used to optimize the potential flow field function,the angles that between velocity vector at different positions in the flow field and the maximum principal stress direction under given load condition,which are maximally fitted.At the same time weight is added into the algorithm to make the algorithm more practical.With such placement trajectories,it is possible to provide the required mechanical properties of the laminates without increasing the weight of the laminate and achieve requirement of lightweight.In the finite element analysis,variable stiffness model is obtained based on the placement trajectories.First,the tension simulation of the linear plate and the variable stiffness plate are carried out,and the improvement of the stress concentration based on variable stiffness is determined by comparison.Then the mechanical properties of the components in the composite laminates are set,fiber and matrix of the linear plate and the variable stiffness plate are analyzed by the progressive failure analysis based on the MCT criterion,and the ultimate load in the two cases are obtained.Finally,the results are compared.Taking laminates with center hole as an example,the stress concentration of the hole decreases by 10.67%,and the ultimate load of laminates is increased nearly 2 times,which verify the effectiveness of the variable stiffness method.