Analysis On Mechanical Properties Of Glare Laminates With Countersunk Bolted Joints Subjected To Out-of-plane Loading

Glare(GLAss REinforced)laminates are hybrid advanced aerospace composites that combine excellent impact resistance and ductility of aluminum alloy materials with the designability of polymer fiber composites.They are now widely used in fairings,skins and other streamlined structure of the aircraft.When assembly separated surfaces,riveting or protruding-bolt connection methods cannot guarantee the flatness of the surface,simultaneously reducing the fluid passability.Overlapping the countersunk head bolts with variable cross-sectional geometric features is an effective method to solve this problem.The non-linear composite laminates perform poorly normal bearing capacity,also the distribution of stress field around the hole is complex.Under the of out-of-plane loading,bolt fasteners and Glare laminates are easily separated by pull-off.Bolt pull-through failure mechanism of mechanical connecting structure is complicated,and it is easily affected by the factors such as the boundary conditions of laminated plate fixation,geometric parameters of fasteners,and the direction of composite material layup.Pull-through impedance performance is the main indicator for the design of composite mechanical connection structures.In this paper,the pull-through mechanical properties of the connection structure between the countersunk head bolt and the Glare laminates are analyzed through the method which combine out-of-plane test and numerical simulation.Firstly,the basic theory about the mechanical connection structure of composite materials is summarized,which provides the theoretical basis for the following research.Then through the pull-through test of connection structure,carry out Parametric research for factors such as bolt diameter,angle of fiber layup,boundary type of solid support,length/width ratio(L/W)of the test piece.Observe and analyze the corresponding failure modes of metal and fiber composites which contained in Glare plates under the out-of-plane loading through water cutting,optical microscopy and other equipment.Second,the single-axis tensile test is used to measure the static strength performance of Al-Li alloy,and the material failure performance and damage evolution of 2060-T8 Al-Li alloy are calculated based on the ductile fracture criterion.Subsequently,the mechanical behavior of the cohesive element of the Glare plates is characterized based on the viscoelastic bilinear constitutive theory and the interfacial mechanical parameters of the metal/fiber interface.Contact property of penetrating slip behavior between bolts and laminatesduring pull-through is defined.Considering contribution of shear stress to material failure,the Hashin three-dimensional progressive failure criterion of composites was modified,and finite simulation model of the connection structure which suffering pull-through failure was established.The load-displacement curves and structural failure modes of the numerical simulation are basically consistent with the test results,verifying the reliability of the simulation method.Finally,the numerical simulation method was used to analyze the influence of the range of the fixed support boundary on pull-through performance of the connection structure.The finite simulation method proposed in this paper effectively depicts the progressive failure process of the out-of-plane pull-off of the connection structure between the countersunk head bolt and the Glare laminate,also accurately predicts the pull-through impedance performance of the structure,which providing the reference for the optimized design on composite mechanical connection structure in the aviation technology field.