Research On The Influence Of Hole Diameter And Hole Position Deviation On The Strength Of Double-bolted Connection Between Composite Laminates And Metal Plates

Bolt connection is widely used in composite structure of aircraft because of its high reliability,easy disassembly and repair,and high load transmission.In this paper,the influence of the hole diameter change and hole position offset on the strength of the double screw single shear joint is studied by means of experiments and finite element numerical analysis.(1)The static strength tensile tests of carbon fiber composite laminate and metal plate double-bolted single shear connection structure under different combination of repair aperture and different bolt hole offset were carried out.The test data,failure mode of composite specimen and overall structure deformation state were analyzed.The flow of three-dimensional progressive damage analysis method was explained,and the composite laminate was established in commercial software.A user-defined subroutine is developed.The3 D Hashin failure criterion is embedded in the analysis of contact nonlinear connection.The progressive failure analysis of composite laminates with double-bolted single shear connection is realized by using Camanho damage expansion coefficient.The accuracy of the finite element model is verified by the test results.(2)The influence of different bolt hole diameter and hole offset on the characteristic stage,initial strength,ultimate load and bolt load distribution of load displacement curve of double-bolted single shear connection structure under standard connection condition is analyzed.The results show that the stiffness of the connection structure will decrease obviously after the damage of the composite material,and the load displacement curve presents bilinear characteristics as a whole;the initial strength of the structure increases with the increase of the bolt diameter,but the initial strength of the structure basically remains unchanged with the increase of the hole diameter offset;within a certain range,increasing the bolt diameter(reducing W/D)can improve the connection performance of the structure,and significantly improve the hole edge The load distribution of the two bolts is different,and the load of No.2 bolt is higher than that of No.1bolt.(3)The progressive damage propagation process of composite laminates with different bolt diameters and hole offsets is studied.The damage mode is consistent with the experimental results.The results show that the change of bolt hole diameter at the loading end and fixed end has no effect on the failure mode of composite laminates,and the connection structure is load-bearing failure;when the hole offset at the loading end is less than 4 mm,the composite laminates have net section tensile failure at No.2 bolt,and when it is more than 4mm,the composite laminates have half section tensile failure,and the hole offset at the fixed end has no effect on the failure mode,and the specimens are in 2 The net cross-section tensile failure occurred at No.1 bolt.Compared with the experimental results,the maximum relative error is less than 8.9%,which is acceptable in engineering.