Study On Mechanical Properties Of Plate-shell Structure With AFP Variable Stiffness

In the aviation industry,composite materials are increasingly being applied to large complex substrates because of the advantages compared to traditional materials.AFP(Automatic Fiber Placement)technology has shown a powerful advantage for the formation of complex large curvature composite components,as well as a great deal of flexibility for composite laminates of various geometries and laminates.In addition,the unconsolidated variable stiffness laminate structure can be realized by laying the preferred curve path along the layer,so as to make full use of the anisotropic material characteristics of composite,so that the material distribution is more conducive to the structural bearing direction.Therefore,it is very important to study the mechanical properties of the shell structure with variable stiffness mechanical properties.According to the discrete idea,the fiber angle is linearly constrained along the single direction and the fiber translation method,the finite element model of the variable stiffness laminated plate is constructed by MATLAB program and the finite element software.The finite element modeling method and the analyze validity of the simulation results is proved by comparing with the experimental results.Based on the Hashin criterion,a user-defined subroutine was designed.Considering the degradation of the material and the interface damage of the ribs and the skin,the progressive failure analysis of the composite stiffened plate were carried out under the two conditions of compression and compression-shear composite load.Through the comparison of the loaddisplacement curve of the stiffened plate and the variable stiffness stiffened plate,the buckling process,the matrix and the fiber failure,the interface failure under the compression load,and stress distribution and failure mode analysis the stiffened plate under the composite load to study the mechanism of variable stiffness skin for the overall mechanical properties of stiffened plates.The results show that the variable stiffness stiffened plate with the design of the load path has higher bearing performance.Variable stiffness skin makes the load distribution to the surface with a stronger carrying capacity of the fiber components,so that the overall deformation of the stiffened plate is more uniform distribution,reducing the stress concentration area.Carrying capacity is affected by load conditions and paving angle,Therefore,for the structure of complex conditions,it is possible to design the laying angle according to the load transfer path to meet the demand for mechanical properties.The progressive failure analysis was carried out on laminates with delamination defects,studying the influence of the variable angle laying on the sub-layer buckling,fiber,matrix failure,delamination expansion and residual strength.The results show that the use of the variable stiffness layer improves the buckling load of the lower sub-layer,at the same time to a certain extent,hindered the destruction of fiber.It is not possible to improve the residual strength of the laminated plate only by adding the variable stiffness layer only in the stratified layer,but still has a significant effect on the expansion of the layer.