The Study On Bearing Performance Of Composite Bolt Joint Structures With Delamination Defects

Carbon fiber-reinforced epoxy-based(C/E)composites have high specific strength and specific modulus,high temperature resistance,fatigue resistance,and good thermal stability.Their manufacturing costs have decreased significantly recent years,and their application range has become wider.It has become a major advanced composite material and has been widely used in aviation,aerospace,defense and military industries.The use of composite materials on aircrafts has become an important indicator of aircraft's advancedness.It is not only applied to the sub-load structure but also be used to the main bearing structure.In the assembly process of large-scale C/E composite parts for aerospace,a large number of riveted or screwed holes are required to connect,which makes the quality of the hole a key factor affecting the strength and fatigue life of such components.However,C/E composites are characterized by unique anisotropy,non-uniformity,low bonding strength between layers,and sensitive to temperature,which can easily cause delamination,burrs,tearing,etc.in the process of making holes.The delamination damage caused in the process of making holes is likely to reduce the mechanical load-bearing properties of composites.Therefore,it is necessary to study the bearing performance of the composite bolted structures with delamination defects.In order to solvethe above problems,we used the ABAQUS to establish a composite material open-hole plate model and composite single bolt double shear connection structure model.In this paper,the cohesive force model is used to simulate the delamination behavior of composite plates.The SC8 R shell element was used to simulate the composite single layer board and the COH3D8 cohesive element was used to simulate the interlayer glue layer.The load-bearing capacity of the composite open-hole plate and the bolted connection structure with ideal and defective holes under static tensile load was simulated.The calculation results showed that the layered cavities defects reduce the static tensile load-carrying performance of the composite material opening plate and the single-nail double-shear connection structure by 1.7% and 3.0%,respectively,with little effect.In order to verify the accuracy of the finite element model,the static tensile test of the composite hole plate and the bolt connection structure was carried out.The test results show that the layered cavities defects reduce the static tensile load bearing performance of the composite material open-hole plate and the single bolt double shear connection structure by 3.7% and 1%,respectively.And the accuracy of the finite element model is proved by comparing the calculated ultimate load with the experimental results and the damage morphology of the test specimens.At the same time,the fatigue test of the composite material open-holeplate and bolt connection structure with ideal and missing holes was carried out.The experimental results show that the layered defects produced during the hole making of composite materials greatly reduce the fatigue life of open-hole plate and bolted connections.Using the established finite element model of the composite material opening plate and the connection structure,we analyzed the bearing performance of the hole-making delamination defect on the composite material open-hole plate and the connection structure under the static compression load.The calculation results show that the layered hole delamination defect has little effect on the compressive load bearing performance of the connecting structure,but it has a certain influence on the compressive load bearing performance of the open-hole plate,which is reduced by 13.4%.At the same time,the paper simulates and calculates the effect of the layer defect angle on the bearing performance of the connection structure.The calculation results show that the layer defect angle has little effect on the bearing performance of the connection structure.