The Static Dynamic Characteristics Analysis Of A Truck Frame And Research Of Structure Optimization Method

As the main load-bearing part of a truck, the frame connects and sustains each assembly while bearing every kind of external loads. Therefore, its performance affects the whole design of trucks directly. With the rapid development of computer technology as well as the improvement of numerical analysis theory and optimization design theory, it is able to use finite element method to analyze the static and dynamic performance of the frame accurately. It has been an important way to raise each performance of trucks, reduce design and manufacturing costs and enhance market competitiveness by optimal design based on the results of the FEM analysis.The analysis of static and dynamic characteristics for the frame structure has been well developed, but the optimization techniques still remain a level of considering single load-case and single objective. Because of a variety of loads, the complex typical working conditions and the strict requirements for trucks, the simple optimal mathematical model could not describe the optimization problem accurately. Although the topology optimization, shape optimization and size optimization has been widely used in the design process of the frame, but studies for combined use of each are still rare.In this paper, boundary conditions and loads of the frame was properly simplified, and four typical working conditions of the frame were taken into consideration. Finite element model of the original frame was established using the FEM software named Hyper Works, and static dynamic characteristics were analyzed. Results show that the static strength and stiffness of the frame could meet the design requirements, and there is a great safety margin for lightweight design. But the initial three order natural frequencies could not meet the design requirement because they are in the range of vibration frequencies of pavement loads and it is easy to induce the phenomenon of resonance.For the defect that low-order frequencies of the original frame are in the range of the resonance frequencies, author proposed a multi-objective optimization program which is better conform to actual operations. The objective of low-order frequencies based on mean-frequency formulation was developed, while objective of multi-load compliance described by compromise programming method was formed. The multi-objective optimization problem was graded by multilevel tolerant sequential programming approach, and the influence of tolerance coefficient on the optimization results was discussed. The optimization results show that the first level objective and the second level objective mutually restrict each other. The first level objective would demonstrate a better optimization result while a smaller tolerance coefficient is chosen, otherwise the optimization effect on second level objective would be more significant. The value of tolerance coefficients would affect the number, shape and relative positions of cross beams in the topological configurations. The new frame structure which is avoid the range of resonance frequencies was obtained through the multi-objective topology optimization.Based on the results of multi-objective topology optimization, the new frame structure was set by the reference of the similar type trucks. Finite element model of the new frame was established by using shell elements, and the thickness of each beams are set as design variables. Lightweight design was implemented by using the size optimization. Compared with the original frame, the strength and stiffness of the new frame could meet the design requirements while the low-order natural frequencies avoided the range of vibration frequencies. The quality of the frame was reduced 698.62 kilogram, the effect of lightweight design is obvious.In this paper, a comprehensive technical process and research approaches for analyzing the static and dynamic characteristics of the frame by using the finite element method were formed, at the same time, the engineer could improve the performance and reduce the weight of frame by using the topology optimization and size optimization. This can provide guidance and reference for related researches.