Effect Of Gap-Filling Compensation On Mechanical Properties Of Composite-Aluminum Connection Structure

As the main aviation materials,composite materials and aluminum alloys have a large number of assembly relationships in aircraft structures.In the case of manufacturing deviation and assembly deviation,there will be a gap between the mating surfaces in the component assembly process.When the assembly gap exceeds a certain range,corresponding gap-filling compensation measures must be taken.Compared with the assembly and connection of the same material,the influence of gap-filling compensation on the connection performance between composite and aluminum alloy is more complicated.In this paper,a composite wing box structure is taken as the research object,aiming at the problem of gap-filling compensation of composite panel,spar and aluminum alloy wing rib,an analysis method combining test and simulation is established to explore the influence of gap-filling compensation technology on the mechanical properties of composite-aluminum alloy connection structure,in order to provide theoretical gap-filling compensation scheme for practical production engineering Basis.The main research work of this paper includes:(1)A simplified model of composite material-aluminum alloy with uniform gap is established,and a new gap manufacturing method is proposed.this paper analyzes the existence of assembly gap between the composite panel,spar and aluminum alloy wing rib,and abstracts the double end clamped assembly model and single lap tensile mold according to the bearing characteristics and stress conditions of the structure when it is assembled and in service under load;the uniform gap is manufactured through the steel gasket,and the assembly sample and tensile sample are established.(2)Based on the double end clamped assembly model,the experiment of the influence of gap-filling compensation on the mechanical properties of the structure during assembly was carried out by using the assembly test bench to simulate the application of bolt clamping force.The local strain distribution on the surface of the specimen is obtained through the strain gauge test,and the strain field of the specimen surface measured by 3D-DIC is combined to obtain the influence of the gap-filling compensation on the surface strain of the specimen;through the cohesive element of the finite element,the interlayer stress and damage are analyzed.The results show that with the increase of the gap,the surface strain of the specimen increases,and the range of interlayer stress damage at the edge of the composite material hole and the edge of the bolt washer becomes wider;gap-filling compensation can greatly reduce the bending deformation of the specimen,restrain the damage degree of interlayer stress,but also increase the strain of the bolt extrusion area.In general,the compensation effect of liquid gasket is slightly better than that of peelable gasket.(3)In the case of different conditions of assembly gap and bolt clamping force,the influence of gap compensation on the tensile mechanical properties of composite aluminum alloy connection structure was studied.Based on the single lap tensile model,the static load tensile test was carried out to test the ultimate load and tensile stiffness of the tensile joint under different clamping forces and gap-filling compensation modes,the influence law was analyzed.Based on the three-dimensional Chang Lessard failure criterion and stiffness degradation criterion,the progressive damage analysis model of the composite-aluminum alloy single lap tensile joint is established by using the user subroutine USDFLD of ABAQUS,and the damage initiation,damage propagation and ultimate complete failure process of the joint are analyzed.The results show that as the assembly gap increases,the ultimate load and tensile stiffness of the composite-aluminum alloy single lap joint decrease,the secondary bending phenomenon of the joint becomes more obvious,and the strain and damage concentration range around the bolt hole become larger.After the shim is added,the joint’s ultimate load,tensile stiffness and hole edge damage changes have obvious gain effects.Under the same shim thickness,the secondary bending deflection of the peelable gasket is less than that of the liquid gasket,and the damage suppression is good.When the bolt clamping force is too large,the tensile mechanical properties of the joint are weakened.