| Durability design sensitivity analysis (DSA) of flexible mechanical system has not been investigated well because it involves flexible multi-body dynamic analysis, structural analysis and dynamic stress computation, and fatigue life prediction. Moreover, due to the use of the peak-valley editing and rainflow counting procedure in fatigue life prediction, an analytical relationship between the dynamic stress and the fatigue life cannot be obtained. Thus, it becomes very difficult, if not impossible, to obtain the fatigue life design sensitivity analytically.; The objective of this research is to develop efficient and accurate continuum-based two-step hybrid durability DSA and optimization methodology for flexible multi-body mechanical systems to support durability-based design. To achieve this, the following tasks to be carried out:; First, an integrated computer-aided structural durability analysis procedure is presented for continuous design analysis and predicting the durability of structures in early product durability evaluation, which includes flexible multi-body dynamic analysis, finite element structural analysis and dynamic stress history generation, and fatigue life prediction of the critical component.; Second, a hybrid durability DSA method for the flexible multi-body systems is proposed. In this method, a continuum-based integrated dynamic stress DSA method is developed to predict the dynamic stress history of the flexible components based on design perturbations; and then the overall finite difference method is used to compute the design sensitivity of the fatigue life calculated based on the predicted dynamic stress history.; Third, a continuum eigenvector DSA method is presented. Since the component modal synthesis method is used to approximate the elastic deformation of the flexible bodies, mode DSA is essential to get accurate dynamic stress DSA. An continuum-based iterative algorithm for eigenvector DSA is developed. Advantages of this method are its efficiency, accuracy, and the fact that only a very small set of eigenvectors is needed for calculating the eigenvector design sensitivity.; Fourth, an optimization methodology for the flexible vehicle body structures is presented. This method provides an efficient and reliable optimization design tool in the pre-prototype and prototype development stages, and fatigue life DSA can identify the weak locations and give useful information to improve the product design, thereby reducing the expensive and time consuming design process significantly. |
