| Structural adhesively bonded is a new structural connection technology for automotive, which has higher flexibility to join different materials, allowing the choice of better material for each component of a structure. It can solve the problem that conventional joining methods faced resulting from the body material updating and its industrial applications. To benefit from this advantage this kind of jointing has been much accounted of and increasingly being used in the automotive industry. Moreover, adhesively jointing technology is one of the key techniques for lightweight of automobile, which also presenting better leaktightness and fatigue properties comparing other mechanically fastened joints, such as spot welding. Therefore, mastering the strength prediction theories and adhesives design methods, as well as mechanical property of adhesive layer has not only important practical significance to design and optimize bonded joints, but also far-reaching strategic significance to improve independent R & D capabilities for lightweight of automotive.In the development flow of automotive design, conventional adhesives are commonly used for sealing, damping and strengthening, while less used in structural jointing for bearing component or half-bearing component. Successful cases of adhesives design for this goal mentioned have not been achieved in vehicles of home products. Adhesives will be developed towards structural jointing as the high strength aluminium and magnesium alloy, even non-metal materials extensively being uesd in the manufacture of automotive, which converts the assembly line from welding to"mix-mode jointing". In light of above mentioned situations, for satisfying the requirement of autobody engineering design, it necessary to carry on the research on static strength character of adhesive joints and to propose effective method of strength prediction to assess jointing design for practical application.This work is funded by"863"Project of China (No. 2009AA04Z101), the Key Project of the National Natural Science Foundation of China (No. 10932003), carries out researches on the static strength character of single lap adhesively joints based on expermential and simulation methods.At the present time, lap jointing is generally used under shear bearing with tension loading in the autobody structures, in respect that adhesive shear strength shows the outstanding performance for load bearing. And the single lap joints are easy to be realised in the design, as well as being satisfied manufacturing process and costing control. However the stress distribution of single lap joints is complex, factors having influence on joint strength is complicated, and simulation methods and design rules are still controversial issues. Depending on the situations mentioned above, a uniform adhesively expermental process flows is built basd on contrastive analysis. Secondly, the stress of adhesive layers is computed and prediction is carried on according to the stress criterion. The trapezoid cohesive mixed-model and adhesive element are built. And Latin Hypercube method is used to quantify the effect of the factors and to propose a predictive equation for joints strength based on experments and simulation. In the end, mechanical properties are respectively explored under two thermal fields which providing the effective guiding for adhesive design. The main contents are as follows:1. Adhesive bonded process and testing systemBase on the adhesive theory, the research of key process parameters of adhesive is carried on, such as surface treatment, adhesive painting and curing. The adhesive bonded process and testing system are built according to the experiment results of comparing the strength of joints under different cases, and the reliability of the process is proved at the same time. The research work mentioned above can supply a great help for high quality, normative and uniform SLJ, which is also the base of performance analysis for adhesively bonded. Strength tests under tension loading of typical joints have been conducted. From the tests, the basic criterion of adhesive design has been presented, which supplied the research object.2. Strength prediction and stress analysis for adhesive layer based on analytical modelA stress analytical model considering the elastic deformation of adhesions is created which can be used for adhesively joints with different materials. At the same time, the model based on beam theory is built which considering the bending effect. The end load of unbalanced joints is obtained which helps enlarging the scope of application of beam theory model. Verification of the two analytical models has been done using the FEM models with refinement mesh. And according to the models, strength prediction of SLJ was proceed under the criterion of stress, and the results can helps investigating their applicability in addition.3. Numerical realization of cohesive element of adhesive layer in FEM simulation A cohesive mixed-mode damage model is created; while the damage initiation criterion and failure criterion are established. Numerical realization of eight nodes brick and plane elements of adhesive layer are implemented based on finite element method. Adhesive toughness is gained by fracture mechanics test using the equivalent creak length. In addition, the cohesive parameters are studied. Finial, the FEM of adhesively joints is done successfully.4. Influencing factors analysis and strength prediction based on experimental designBased on orthogonal test and Latin hypercube method, physical and computer design of experiments are carrying out to evaluate the strength of adhesively bonded which considering many factors during the process. The regression model between strength of SLJ and influencing factors were established. This method of experimental design for predicting the strength with various parameters is an effective way which supplies the great help for studying the relation between strength and factors.5. Experimental research on strength of adhesively bonded under temperature fieldExperimental researches on strength of bonded were carried out under constant temperature fields and cycling temperature fields, during which the factor of storing time was considered. The reason for strength decreased was explored using the theory of thermal stress. Based on the above models and results, the effective methods for predicting strength under different temperature fields were investigated.The dissertation researched the stress distribution, strength performance and the influencing factors of adhesively joints based on physical tests, analytical model as well as FEM method. The research results have significant guidance meaning in the design of adhesively structure for automotive.
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