The Analysis Of Strength And Failure On The Hybrid Jointed Structure Of Composite Material And Metal

In reality,affected by many factors,the load-bearing reliability and durability of composite and metal jointed structure are uncertain,and there are lightweight requirements for joints in the aerospace field.However,the existing research is less than that of pure composite or metal joint.The application of composite laminate and metal bolted connection in aerospace field is inevitable.The lightweight and reliability of joint has always been the main concern of joint design.There are some problems in hybrid joint,such as load transfer efficiency,reliability,life span and so on.It is necessary to study the mechanical connection of composite and metal,but the research on hybrid joint design is relatively less.In this paper,firstly,the nonlinear analysis theory and formula of composite metal hybrid connection structure are introduced.Combined with the research object of this subject,the main points of nonlinear finite element analysis in this paper are described.Combined with the literature,the method of nonlinear analysis in this paper is given.Combining the Hashin failure criterion and the improved Yamandasun failure criterion with comanho stiffness reduction method,the user-defined field variable subroutine of usfld is compiled.Two kinds of stiffness degradation models of composite materials are established.Combined with the ideal plastic model of metal,the finite element simulation analysis of composite metal bolted joint is carried out.Four kinds of finite element models are established according to four kinds of parameters: load direction,nail hole matching,embedded metal between nail holes and stiffness matching of connector.The displacement,stress,load limit and material damage of the model are analyzed respectively,and the influence of four kinds of parameters on the connection strength and failure of the structure is studied.The results show that the results calculated by Yamanda-sun failure criterion are more conservative than those calculated by two-dimensional Hashin failure criterion,and the failure element propagation along the circumferential direction of the hole is more obvious.According to different research purposes,the corresponding test samples were prepared and the ultimate tensile test was designed and carried out.The deformation,strain,failure mode and load-displacement curve of each test sample are analyzed.The influence rules of load direction,screw hole matching,embedded metal between nail holes and stiffness matching of connecting parts on deformation,failure and ultimate bearing capacity of the structure are obtained.The results show that the bending of the joint is closely related to the relative thickness of the laminated plate and aluminum alloy,and the matching of the nails and holes;The connection structure matters with the stiffness of the connection parts;The change of the composite layups will lead to the failure of the composite in different forms.In the tensile failure,split and extrusion failure,the bearing capacity of the composite is higher under the extrusion failure;The four kinds of parameters will affect the ultimate bearing capacity of the structure,and the ways are different.Based on the idea of comparing finite element simulation with experimental study,the strength and failure of composite-metal hybrid connection structure are analyzed,and the influence of four kinds of factors on the strength and failure mode of structural connection is discussed,which has certain guiding significance for joint design in engineering practice.