Crash energy absorbers in the form of thin walled tubes play a significant role in mitigating the harmful effects of frontal vehicles accidents on occupants. Specific energy absorbed (SEA), which is the ratio of impact energy absorbed to mass, is usually used to evaluate the efficiency of crash energy absorbers. A good design of a crash energy absorber must maximize the amount of impact energy that can be absorbed with a certain weight. The formal approach that has been used to improve the design of crash energy absorbers is to employ optimization to search for the optimum thickness distribution that maximizes SEA. This approach can be conceptualized as searching the design space in only one dimension (thickness). In this paper, a new dimension is added to the design space (material type). The proposed approach considers the type of material as a variable. An optimum design is then found by not only searching for the optimum thickness distribution, but also by selecting the optimum material type. The approach is demonstrated to the design improvement of a crash energy absorber in the form of a thin walled tube of square cross section. Steel and magnesium have been used as the two material alternatives. Magnesium has been selected due to its low density that had made it a promising candidate for use as a structural material in the automobile manufacturing. The results have shown that following the proposed technique, SEA has been increased by 54% compared to the value obtained through following the formal design optimization approach.

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