Research On Strength And Failure Mechanism Of The Join Technology Of Composites

Fiber reinforced resin matrix composites have excellent properties such as high strength,high rigidity,fatigue resistance and corrosion resistance,and widely used in aviation,railway traffic,shipbuilding,construction and other fields.The application of composite structural parts inevitably occurs in the joint structure,and the joint is the weakest part of the overall structural strength,so most of the failure of the structural parts occurs at the joint,the strength study of the joint structure and the failure mechanism for the structure The stability and durability of the design are important.In this paper,the strength properties and failure mechanism of composite joints are analyzed by finite element simulation and experimental analysis,and the failure mechanism of joint structures is further studied by means of material fracture analysis.The main works as follows:(1)The finite element software ABAQUS and test were carried out to verify the influence of the composite joint structure and the design of the layup scheme on the strength.It was found that Composite rubber-spiral hybrid joints have higher bearing strength than bolted joints;When the laminate layer angle of the composite layer is 45°,the partial crushing strength of the sheet hole is higher;For the joint structure subjected to the axial tensile load,the 0°layer in the axial direction is higher,and the tensile strength of the integral composite joint structure is higher.Therefore,the composite structure ply design should select the corresponding ply design according to the specific bearing mode,so that the structure has higher bearing capacity.(2)Through the tensile-shear test,the cross-section of the composite with different damage degree was obtained.Through the mechanical analysis and the macroscopic and microscopic structural analysis,the failure mechanism of the composite joint structure was studied.It is concluded that the carbon fiber tow of the bolt-connecting structure is deformed by the bolt pressing force and transmitted to the resin matrix,so that the fiber is buckling and the resin matrix is squeezed into a cluster by the short bundle of the fiber which is uniformly distributed.The structure is uneven and weak areas appear.The rubber-spiral hybrid joint structure exhibits tensile fracture failure;the carbon fiber tow at the fracture is pulled out from the epoxy resin matrix under tensile-shearing and damages the fracture,and the joint structure exhibits tensile fracture after reaching the ultimate load.And the adhesive between the sheets after the redistribution of the load has a retarding effect on the destruction of the fibers.(3)Finally,it was found that the composite joint structure was forced to pull out the fibers around the nail holes,and the matrix was damaged until the components collapsed.Factors such as material strength,bolt strength,strength of the rubber layer and bolt width to diameter ratio will all be factors that affect the failure of the joint structure.The research on the strength and failure mechanism of composite joint structure provides a design reference for the optimization of composite joint structure,which has important practical application value.