A metamodel based approach for the shape optimization of a front rail

Abstract

In crash cases, injuries and loss of lifes are inevitable situation most of the time. There are some another considerations in economic, sustainability and production areas from the manufacturer's point of view. There have been some technologic developments in automobile and aerospace industry that pushes manufacturers to produce safer and more profitable products. Bumper, rocker, rail upper and front rail are the main crashworthiness structures for vehicles design. Front rail is one of the most important impact absorber among the all crashworthiness structures in vehicle design area. It is noted that front rail plays the most critical role during the crash in crashworthiness structures. The fuctions of front rail are transmissing the crash force to the middle crumple zone, absorbing impact energy and providing a favorable buckling form during the crash. Absorbing impact energy is the most important parameter among all functions for passenger safety. Before the crash, there is a high kinetic energy for passenger between vehicles or between vehicle and static objects. One of the most considerable condition for crash cases is passenger safety. Crashworthiness structures are the main provider for this case. They absorbs the some portion of kinetic energy and transmits the left part into the passenger zone. It is important for passenger safety that the more energy absorbed by crashworthiness structures because passengers are exposed less impact energy. There have been some optimization studies and design innovations for crashworthiness structures. Also, some material applications are made to overcome in absorbing impact energy consideration for crashworthiness structures. Addition of sub-structures into crashworthiness structures, optimizations for getting less weight structures, structural optimizations are some studies for crashworthiness structures. In real crash test centers, speed of vehicles are specified as encountered in urban areas. Most of the crashes happens in city streets and real tests center used these kind of speed levels. Design modifications, material applications and comparing cases for different speed levels are the main objectives in this study. Firstly, a design approximation is made to absorb more impact energy in optimization cases. Embosses are created on the front rail for this purpose. Relations between embosses and thickness of front rail are specified as design variables. Another purpose of creating embosses on the front rail is getting appropriate buckling form during the crash. Embosses are provides this problem in optimization study. Secondly, some material applications are made for economic and flammability considerations. In crash scenarios, a fire situation can come up and it might melt the crashworthiness structures. Another consideration is fuel consumption. Selecting different materials provide us to have lightweight structure. Specific Energy Absorption (SEA) is another parameter for material selection for crash worthiness structure. Three different materials are used for every optimization process in this study. Lastly, two different speeds are selected to see how front rail behaves under low and high speed conditions and their buckling forms are examined. A stochastic optimizaiton method is selected for optimization processes. Genetic algorithm is used for all optimization studies. Metamodel optimization technics are used with the usage of genetic algorithm. D-optimal point selection is used for sampling process and sequantial response with domain reduction method is used for the selection of next iteration sampling design space. In result section, all six cases are compared with each other for crashworthiness indicators like SEA, peak force, mean crash force et al. After all optimization processes importance of design variables are discussed and metamodels of optimization processes are shown. Von-mises stress distributions of front rails are shown for all six cases to visualize stress distribution. Advantages and disadvantage of all six cases are discussed and their efficiency on this study are indicated.