Research On Variable-stiffness Composite Thin Plates With Holes Of Buckling And Failure Under Compression

With the development of the fiber placement,the existing automated fiber placement devices have been able to achieve the variable angle placement of fiber tow,making the angle in continuous change within the same layer.Compared with the traditional fixed angle placement,it can increase the flexibility of the design and more adequately take advantage of the directional characteristics of the composite materials,making possible to improve the performance of the components or reduc e component weight.In practical engineering applications,we need cut-out on laminate plates for demand such as connection.Research of the relationship of variable-stiffness composite plan.Therefore,based on the opening variable-stiffness of laminated plates and stiffened panels as the research object,this paper study the relationship between fiber angle with the compression buckling performance.This study has a certain role for its engineering applications.The main contents:Considering the characteristics of variable-stiffness laminated plates and the advanced fiber laying technology,This paper puts forward five design principles based on the curve of fiber laying,for subsequent reference criterion of layer design.In order to overcome the weakness that the finite element software can not directly establish the limits of variable stiffness layer,this paper uses the MATLAB software and ABAQUS software to establish the finite element analys is model of variable-stiffness laminated plates.The ABAQUS is used to obtain the discrete units,and the simulation calculation.The MATLAB software is used to obtain the fiber orientation information of discrete unit.For the study of the buckling behavior and failure of the variable-angle-laminated composite plate under compression loading,three buckling analysis methods were carried out to model the variable-angle-laminated composite plate with holes: linear buckling analysis,linear buckling analysis with residual thermal stresses and non-linear buckling analysis with initial imperfections,and experiments were conducted to verify the rationality of the three methods.It was shown that linear buckling analysis method with residual thermal stresses agrees well with the experimental results,which only differs by 0.63%.With this method,the residual thermal stress distribution characteristics and stress level were discussed to find the stress distribution nephogram and the stress distribution law.And then the inf luence of residual thermal stress on the buckling behavior of the variable-angle-laminated composite plate was calculated.The results showed that the residual thermal stress has little inf luence on the buckling behavior of the straight fiber laminate only with a 0.6% increase,and the buckling behavior of the variable-angle-laminated composite plate improves signif icantly,which increases up to 23.40%.This paper adopt Hashin failure criterion to calculate the failure load of of the variable-stiffness laminated plates with cutouts.The results show that the weakening effect of the hole makes that the open pore structure has a lower failure load compared with complete laminated plates.But compared with the traditional uniform-stiffness of laminated plates,the curve of fiber laying makes the effect on the failure load reduced from 32.2% to 27.1%.On the basis of the variable-stiffness laminates finite element model,this paper established the finit e element model of variable-stiffness stiffened plates and introduced interface unit to simulat connection interface between stiffener and the skin for studying stiffened composite plates the compression buckling and failure process.The results shows that with the increase of the rate of curvilinear-fiber laying,the buckling load of variable-stiffness stiffened plates is decrease.But variable-stiffness stiffened plates have higher failure load and it appears damage later than conventional stiffened plates.After damage occurring,it has good bearing capacity,and the post-buckling load of variable-stiffness stiffened plates is better than the traditional stiffened plates.This paper analyzed the influence on buckling load and failure of fiber curve angle.The results show that with fiber angle is more perpendicular to the loading direction,the higher the overall s tiffness of the skin,buckling load will also continue to increase.In this paper,we further study the effect of hole size,the results show that with the increase of skin hole size,damage occurred earlier and earlier,and for the same hole size of variable-stiffness stiffened plates.As the ratio of the curvilinear-fiber layer increases,the opening effect of holes on failure load reduced to 23.0% from 8.2%.