The Strength Research And Failure Analysis For Composite Joint Structure

Composite material is widely used in aviation and aerospace structures. Theapplications change from no load-carrying structure to main load-carrying structure,such as airplane cabin door and stabilizer. Using composite material in mainload-carrying structure, Airbus has30years experience and the technology has alsobecome quite mature. The number of parts and fasteners reduces with the applicationof co-curing and integrated forming, so the load in the rest is bigger. In some specialstructure of the aircraft, the joint structure is used in some parts, which are keptbecause of design, technique or maintenance needs. So the joint between compositematerial structures is unavoidable and the joints become the key part of compositematerial structure.This paper is research on composite material in aircraft structures. Based onthree-dimensional progressive damage theory, adhesive bonded joint and bolted joint,which are typically used in aircraft structural components, are analyzed by thetechnology platform of finite element analysis software ANSYS. Three dimensionalparameterized progressive damage model of adhesive bonded joint and bolted jointare developed and the influence of geometric parameters on the structural strength isanalyzed. As to composite material failure forms: Matrix crack, Delamination, Fiberbreakage, Fiber-matrix shear, failure judgment program is written by APDL (ANSYSParameter Design Language) based on composite structure theory, progressivedamage theory and stiffness degradation theory. The result of numerical simulation iscompared with the experimental results of reference and the accuracy of failurejudgment program was verified. The detail research contents are as follows:Firstly, three dimensional model of bolted joint is developed and strengthprediction of bolted joint is carried on with stiffness degradation program and failurejudgment program. The result of numerical simulation is compared with theexperimental results of reference and the accuracy of failure judgment program wasverified.Secondly, parameterized progressive damage model of bolted joint is developed by the technology platform of finite element analysis software ANSYS. Effects ofsome parameters on strength of bolted joint are analyzed and some conclusions areobtained. Parameters include the mode of connection, thickness of plate, layersequences of laminates, pre-tightening force and joint dimensions.Thirdly, based on the above analysis results, the progressive damage of boltedjoint is analyzed. The damage extension process of composite material laminate issimulated from initial failure to final failure. Each ply angle of composite materiallaminate is analyzed in detail, especially the ply angle of90°,0°,45°and-45°.Finally, parameterized progressive damage model of adhesive bonded joint isdeveloped by the technology platform of finite element analysis software ANSYS.The stress analysis of single-lap adhesive bonded joint and double-lap adhesivebonded joint is compared detailed. Then effects of lap length and adhesive thicknesson adhesive shearing stress are analyzed and the stiffness of lap plate is also takeninto consideration. In the end, the failure load of adhesive bonded joint is analyzedwith different lap length and adhesive thickness.