Strength And Progressive Damage Research For The Double Nail Bonded-bolted Hybrid Composite Joints

Carbon fiber composite materials are widely used in aerospace related fields due to their excellent performance.With the development of the overall design of aircraft structure,the number of parts and fasteners is greatly reduced,and new composite connection structures and larger connection elements need to be studied urgently.In the composite connection,reasonable boned-bolted hybrid joint can take into account the advantages of glue and bolt connection,which can improve the anti-stripping ability of the structure,but also reduce the stress concentration of the hole edge,which is one of the research hotspots of the current composite connection structure.In this paper,the titanium alloy-composite double nail glue-screw hybrid connection structure is studied in view of the serious end warp and low carrying capacity in the composite single-nail glue-screw mixing connection structure.On the basis of numerical analysis and experimental verification,the influence of parameters on failure load and the process of damage expansion in the mixed connection structure are analyzed,and some theoretical reference is provided for the application of the connection structure in engineering.The study reads as follows:Firstly,based on Hashin failure criterion and material performance degradation criterion,the failure form of composite materialist is determined,and the failure of the coating layer is determined by the secondary nominal stress criterion.The simulation model of titanium alloy-composite double-nail glue-screw hybrid connection structure was established and finite element analysis was carried out by finite element analysis software,and the feasibility of the titanium alloy-composite double nail glue-screw hybrid connection structure finite element model was verified consistently with the test results.Secondly,the parameters such as the paving order,the width ratio,end-diameter ratio and aperture ratio of the composite material were studied respectively,and the influence on the carrying capacity of the titanium alloy-composite double nail glue-screw hybrid connection structure was studied.The results show that the carrying capacity of the mixed connection structure is best when the paving order is3 s,the failure load of the connection structure will gradually rise,but the connection strength will decrease gradually,and within a certain range,the carrying capacity of the connection structure can be improved by the appropriate increase in the end-diameter ratio or aperture ratio,and the carrying capacity of the connection structure will be reduced when the connection structure is exceeded.Finally,the proxy model is created by the Latin super-vertical method,and the multi-parameter optimization design of the hybrid connection structure is optimized,and the optimization results show that the hybrid connection structure has the maximum failure load at 28 mm width,8.5mm end distance and 22.5mm hole distance.And the multi-parameter optimization result is obviously better than the single parameter optimization result.