Research On Adhesive Bonding Technique And Joint Strength Of Aerial Al-Li Alloy Plate

Bonding technique plays an important role in the various fields of the national economy and achieves significant economic benefits. In order to reduce the weight and ensure strength, aluminum alloy is abundantly used in the aircraft structure. Cracks and damages in the aircraft structures which are affected by environment and variable force are produced by long term usage unavoidably, which affect structural strength and flight safety. Compared to the traditional repair methods, such as welding, riveting and bolting, bonded repair of metallic structure has been recognized as an economical and efficient method which has the advantages of extending the service lifetime of damaged aircrafts, reducing the stress concentration of the structure, and simplifying the technique.Factors affecting the bonding quality include operator’s subjective, materials, technology, environment, and so on. Adhesion strength has a larger dispersion,the requirement to its quality control is very strict. Crack even failure tends to be present in the adhesive bonded structures because of the influence of macroscopic defects, stress, interface characteristics, and so on.The dissertation has made experimental study and theoretical analysis for the Al-Li alloy single-lap adhesive joints in aerospace. Material surface treatment, preparation of bonding pieces and influencing factors of bonding quality are studied systemically. This thesis includes the following main aspects:(l)Based on the related standards and practical needs, the geometry of Al-Li alloy bonding pieces is determined. Programs about different metal surface treatment and preparation of test pieces are developed. Through the tensile-shear testing, the optimum preparation process has been obtained, and relevant parameters are determined, involving mechanical polishing, adhesive, process parameters of oxidation and curing.(2) The influences of adhesive layer sizes and bonding gap on the mechanical properties in Al-Li alloy single-lap joint were investigated. The best layer parameters have been obtained comparing the results of experiments, while material weight and savings also have been taken into account.(3)The paper not only built the model of bonding joints and made certain choice about method of solving parameters, convergence criterion, partition principle of element mesh in modeling of bonding joints, but also got the common principle for building metal bonding joint structure model and provided theoretical evidences for the research of finite element modeling and analysis of bonding joint structure.(4)Comparing the results of experiments and finite element analysis, the finite element model has been proved to be correct by measuring the tearing length of glue layer and caculate the failure stress value.The delamination index has been observed from result files.(5)The influence of adhesive layer sizes and bonding mode on the stress distribution of finite element model is studied under the same load, the influence law of superposition length, adhesive thickness and bonding gap on the stress distribution of bonding joints has been obtained.