Improvement Research Of Analysis Method Of Stiffness And Strength For Engine Hood On A Passenger Car For Engine Hood On A Passenger Car

The traditional body structure analysis uses the way that contains both the design process and the physical tests, which are serial organization. Before the stereotypes body often goes through many rounds of stages, such as structural design, prototype vehicle developed, testing, improving the structure, and reproduced a prototype vehicle. As a prototype vehicle production and the revision will take a long time and repeatedly. As a result, the cycle of the body design will be long, and will consume many resources. Along with the rapid development of computer hardware and software, body structure analysis for the body structure is no longer just a post-calibration; body structure simulation has become a means of checking the whole process of body design. As a result, body structure design and analysis of parallel design process will become the new process. Currently, through the body structure simulation analysis, we have body parts or even entire vehicle get along with the stiffness, strength, modes, fatigue strength, formability, safety and other performance indicators, but could not evade the question is :The simulation results and the actual results often has certain difference. Especially the structural analysis of the stamping parts. The main reason is that when we do the structure analysis, we use only nominal thickness to calculate which inconsistent with the actual situation. In 1998, FIAT automobile research institute studied on this issue. They used T-connector for the study and then introduced the changes of the thickness into the model of structure stiffness analysis, and then used the experiment to validate the results. They obtained the conclusion: "As the introduction of thickness coming from forming analysis, analysis accuracy will be improved significantly. Compared with the traditional analysis which use of nominal thickness, we get at least 50% improvement in the accuracy". This article will follow this way, but concentrate on the engineering practice to explore the method how to introduce the material thickness changes coming from forming into structural analysis, and then arrange some performance tests to verify simulation models.The one that began with the CAE analysis of the current situation, as well as pointed out the method of traditional structure analysis. Then leads to the issue of content: Improvement analysis method, which means introducing thickness coming from forming analysis into the structural analysis model to explore the contribution degree to the body parts simulation. The issue of the object is the hood assembly. It was chosen for two reasons: on one hand, as the major part of the engine hood, the inner and outer boards are made by drawing, and the process are representative–it contains both the integrity of the process of drawing and flanging opened. On the other hand, for the hood is a relatively independent assembly, it facilitates us to carry out certification tests. The idea can be finished owing to HyperWorks? 8.0 software powerful functions, by the HyperForm? we get the forming result, by Result-Mapper? we introduce the thickness coming form forming analysis into the analysis of the structure, and eventually get the conclusion. Specifically, this paper introduces the following methods:1. We use the software to establish the inner forming simulation model ,then analysis the problem of the geometry cleanup phase and forming simulation stage in detail,study on how to control the finite element size and the method of meshing. At the end of the analysis, we get the forming results of the inner board of hood. By adjusting the blankholder force,we get a better forming simulation model.2. Introduced the present academic treatment in opening flanging, and take the outer board as the example to propose the new ideas based on the geometry of flanging reconstruction. In essence, this method is constraint geometry to re-establish flanging model. Here need to use the die design features of HyperForm. First use"Addendum"to create consistent with the requirements of the length of surfaces, then use"Binder"to create flange edge, Finally use"Line mapping"to achieve flange original shape. The whole process is simple and effective. On base of this,we establish an outter board forming simulation model, in the light of the actual,we set up four drawbeads. Eventually we get a good forming simulation results. 3. Based on the careful analysis of the various components on the hood assembly, established the structure analysis model of hood assembly contains hood inner and outer board, enforce plate and the hinge. Then do some researches on the connections of them, on this basis, establish the equivalent model of the Hemming connection and glue connection.4. We recommend the method of introduce forming results into structure analysis for two aspects .Take the outer board as an example, detailing the use of Result-Mapper to extract the forming results. Through in-depth study of the practice, find out the methods about how to transfer the thickness of the mapping information to the structural analysis model.5. Imitated the load conditions of the hood on trial, made the uniform loading on improved simulation model and the traditional model, and obtained the simulation result.6. In view of the performance requirements and the hood actual conditions, with reference to foreign standards we experiment of hood assemble such as hood lateral and torsion stiffness test, hood-bending stiffness test and mode test.7. Compared the simulation results with the test results from the quality, lateral stiffness, torsion stiffness, hood-bending stiffness test and mode, we obtain the conclusion by the analysis and the discussion.8. Point out the direction of the method of improvement analysis and the study on hood.We conclude that the results of improved analysis methods inosculate with experimental data in the lateral stiffness and mode analysis. However, it has large deformation, and stress is greater too.As a result of the problems cited improvements on forming analysis is the finite element method multidisciplinary cross-analytical method both from the theoretical to the practical details of operation there are a lot of issues to be addressed. Nevertheless, in the light of the time of study is too short, some specific problems have yet to solve. Facts marshaling as research progressed. Therefore, the only issue is to improve the method of analysis.