Rear middle bumper design of a raised floor bus

In parallel with the development of technology in the automotive industry, from past to present, the usage of motor vehicles have increased rapidly. Together with the increased numbers of motor vehicles acting on highways, the huge number of highway collisions have started to be a critic problem for the nations. The statistics of the World Health Organization show that worldwide more than 1.25 million people die and 20 to 50 people suffer from the highway accidents annually. At this point, integrating systems and structures that take a role on minimizing the impact of collisions on the passenger and pedestrians has become an important issue for the automobile makers. Bumper systems that are integrated to the front and rear ends of the motor vehicles are one of these impact reducers in case that an automobile hits any object or a pedestrian. In this thesis study, it is aimed to review the present literature and applications of the automobile bumper systems and to introduce proper material, production method and design proposals for a rear middle bumper of a raised floor bus by taking the information of the present bumper applications into consideration. This study starts with the review of the definition and functions of automobile bumper systems and the historical development of the present bumper structures. As the driver and passenger compartments in a raised floor bus is in a heigher level than the collision height, the primary functions of bus bumpers differs from the passenger cars. Therefore, the functions of bus bumpers are focused on in details in this study. Afterwards, within the scope of this study, the types of bumper systems that are used in today's automobiles are explained and demonstrated with figures and information about the sub-components of these bumper systems are given in details. In order to explain the importance that automotive bumpers are not only parts that beautifies the automobile body, the current highway standards and regulations that concern the requirements demanded from the bumper systems of passenger cars are shortly described. After the review of general information about the automotive bumper systems, current standards and regulations, in the oncoming sections of this study, the materials and most commonly used manufacturing technologies applied for the production of automotive bumpers are described in details by demonstrating also with figures. By explaining the advantages and disadvantages of each production method, a comparison of these applications are summarized in order to use as a reference during selection of the material and production method proposals of the rear middle bumper of a raised floor bus. In addition to the present applications, the challenges about the bumper materials that automotive manufacturers will face in the future are also shortly mentioned. Prior to the design proposal of the rear middle bumper, as Finite Elements Methods (FEM) is used during the modeling phase of the rear middle bumper, a review about the Finite Elements Methods are given in the following sections of this study. The definition of FEM is explained and approaches used during a FEM study are described. Afterwards, the steps that are followed during a FEM analysis and the advantages of using this method are mentioned. In this study, the present computer aided design applications that use FEM during the design, modeling and structural analysis phases are also stated shortly. Among these applications, Siemens NX that is used during the design steps in this thesis study was explained in details. Taking all these information explained above into consideration, in order to propose design solutions for the rear middle bumper of a raised floor bus within the scope of this thesis study, a systematic design approach starting with definition of the task and preparation of requirements list is implemented. After generating the requirements list, as the following step, by evaluating all the bumper material and production methods explained in the previous sections, two alternatives of bumper materials and production methods are proposed accordingly to the requirements expected from the rear middle bumper. After selection of the bumper material and production method alternatives, firstly the surface modeling is figured out using the computer aided design software Siemens NX. Then, by adding volume on the surface model, the 3D models for both alternatives are generated. In order to minimize the part complexity and accordingly the unit cost, firstly the 3D models are figured out without any reinforcing ribs added on the part. In order to examine the strength of these models, the displacement and stress analysis are implemented in Siemens NX under certain load conditions. The analysis results are evaluated according to the allowed maximum limit values stated in the requirements list. Based on the weak results of the analyses applied for the ribless models, iterations by adding reinforcing ribs are implemented on the models and the analyses are repeated. At each stage of these step-by-step iterations, the figures of the 3D models showing the analysis results are demonstrated and the results are summarized in tables in order to give the reader a clear view. As a consequence of this study, the proper rear middle bumper design solution that meets all the expectations stated in the requirements list is selected. As today's competitive environment in the automotive industry will increase rapidly in the near future, to overcome the future challenges, recommendations for cost reduction and meeting public expectations, such as reduction of environment pollution, are also proposed for the rear middle bumper design in the scope of this study.