Reliability-based design optimization (RBDO) is an effective method for structural optimization due to its ability to take into consideration uncertainties in design variables. Performance measure approach (PMA) based methods are commonly utilized to evaluate the probabilistic constraints of RBDO problems. The advanced mean value (AMV) method is a very commonly used due to its simpleness and effectiveness. However, the AMV method sometimes produces unstable and inefficient results for concave and highly nonlinear limit-state functions. In order to improve robustness and efficiency, many methods have been developed, for example, chaos control based and conjugate gradient-based methods. These methods lead to more stable results as compared with the AMV approach but they are inefficient for use in complex and convex limit-state functions. The RBDO of structural components is often a difficult issue due to complicated constraints. In this paper, a novel hybrid approach, referred to as “hybrid gradient analysis (HGA)” is introduced for the evaluation of both convex and concave constraint functions in RBDO. The HGA method combines AMV and conjugate gradient analysis (CGA). The robustness, simpleness and effectiveness of the proposed HGA method are compared with various PMA methods aimed at reliability such as AMV, chaos control (CC), conjugate mean value (CMV), modified chaos control (MCC), hybrid mean value (HMV) and CGA methods by means of several nonlinear convex/concave limit-state functions and structural RBDO problems. Reliability analysis and RBDO results point out that the HGA approach introduced here is more effective and robust than the well-known approaches.
In literature, a lot of research works have been presented on crashworthiness in order to develop crash performance of vehicles and thin-wall structures. In this research, a new hybrid optimization algorithm based on gravitational search algorithm and Nelder-Mead algorithm is introduced to improve crash performance of vehicles during frontal impact. The results show that the hybrid approach is very effective to develop crash performance of the vehicle components and thin-wall structures.
In this paper, the effect of conventional steel, new generation DP-TRIP steels, AA7108 – AA7003 aluminum alloys, AM60 – AZ31 magnesium alloys and crash-box cross-sections on crash performance of thin-walled energy absorbers are investigated numerically for the lightweight design of vehicle structures. According to finite element analysis results, crash performance parameters such as total energy absorption, specific energy absorption, reaction forces and crush force efficiencies are compared for the above-mentioned materials. The energy absorption capability of steel energy absorbers is better than that of aluminum and magnesium absorbers. On the other hand, the energy absorption capacity per unit mass of energy absorbers made from lightweight materials is higher than that of steel energy absorbers. This advantage of lightweight alloys encourages automobile manufacturers to use them in designing structural vehicle components.
In recent years, there has been a great deal of interest in lightweight vehicle design due to regulations about reducing fuel consumption and emissions. Lightweight design of vehicle components is one of the most important research topics in vehicle design. Developing the optimum structure in the early stages of design process is very important for minimizing the vehicle weight and production costs. In this paper, an automobile hinge component has been developed using PA66 GF60 glass fiber-reinforced polyamide composite materials instead of conventional steel. The automobile hinge component has been conceived using computer aided design software. Topology optimization was made under specific loadings subject to the constraints of finite element method analysis. As a result of this study, optimum dimensions of the component have been obtained and the weight of the component has been reduced via structural topology optimization techniques while satisfying displacement and stress conditions. The results show that composite materials are an important alterative in lightweight vehicle design.
This paper aims to develop a new crash box with improved crashworthiness at reduced cost and weight as a base design for use in the automotive industry. Firstly, a baseline crash box model as presently used by the automotive industry was comprehensively examined by numerical crash analysis using Ls-Dyna software. Considering the initial design geometry, forty-five different crash box designs were developed by making changes in the geometry and wall thickness of the thin walled structures. The effects of the changes in wall thickness and geometry in alternative crash box designs on crash performances such as total energy absorption, peak crush force, mean crush force, specific energy absorption and crush force efficiency were investigated. The optimum crash box design obtained numerically was validated experimentally by means of the drop tower impact system. The numerical crash analysis results clearly agree with the experimental test results. In this study, a new crash box design at a lower cost and performing better in crashes compared with the other forty-six designs has been obtained and can be used in the automotive industry as an energy absorber. The results have revealed that crash box geometry, as well as the number and position of the spot welds and sheet-metal thickness have an important effect on crash performance, weight and cost of the crash boxes.
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