The Main Bearing Composite Joint Scheme And Study Of The Failure Mode

Composite materials with properties of high specific strength,high specific stiffness and design versatility have been applied more and more extensively in the field of aircraft structure.It developed From the initial application in low-load and the secondary stress components of aircraft to the present application in the main bearing components.And the connection problem would inevitably face in the practical application of composite,as well as the most important part of the structure design.Joint scheme is very important in the joint design of large composite structure,particularly in the field of aviation,play a vital role in the safety of the structure.Because of the anisotropy and brittleness of composite materials,many factors that affect the joint strength,and complex failure modes,which requires reasonable design to ensure the efficiency of the joint and the structure reliability.Aiming at some problems of the composite mechanical connection,the paper carried out related research on the mechanical connection design scheme of the main bearing composite materials and the corresponding failure mode of the structure,and mainly carried out the following work that included four parts:The first part,according to the theory of composite mechanical connection design,analyzed the typical failure mode and design form of mechanical connection.For some deficiencies when the metal joint connected with the composite structure,designed a bolted joint scheme for foam inserted top-hat stiffened composite plates to increase the connection efficiency of joint and improve the stiffness mismatch problem when the metal joint connected with the composite.And by selecting the VARI(Vacuum Assisted Resin Infusion molding)made the joint connection structure.The second part,aiming at the designed composite joint connection structure,in order to comprehensively analyze the influence of the designed geometric parameters on the joint mechanical property,established three test loading scheme,by the method of the three point bending test,then tested the mechanical performance of bolted joint.This paper changed the degree θ of the up clamp plate and the length Lx of the inserted foam block,after getting and converting the experimental data studied the influence of the variational design on the joint bending performance according to the equivalent bending moment-displacement curves.Finally gave some suitable design optimization parameters of the joint scheme.The third part,according to the typical mechanical connection failure mode and influencing factors of composite materials,analyzed the structure of the designed joint.In the whole process of mechanical test observed the failure modes of the joint connection structure and the specific change among them under the different loading scheme,summarized and analyzed the seven generated kinds of failure modes and their causes under the different design parameters.Finally obtained the relationship among the design parameter,loading method and failure mode of the joint connection structure.The fourth part,by using the finite element software ABAQUS,set up a studied model of the bolted joint structure for foam inserted top-hat stiffened composite plates and by using the numerical simulation method studied the designed joint structure.Based on the failure distribution clouds analyzed the various failure modes that occurred under the different loading ways.By comparison with those phenomena of structure failure that observed in the mechanical experiment verified the analyzed result,and verified that through reasonable parameters optimization can change the failure form of joint connection structure,reduced the criticality level of structure failure.It provided the theoretical basis for improving the joint efficiency and reliability of composite mechanical connection.