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To investigate the e ects of electric power assisted steering ( EPAS ) on a vehicle's steering performance, this paper explicitly proposes several indices, such as steering sensitivity and road feel, for evaluation of steering performance. Then a single-track car model with lateral and yaw movement is considered and an EPAS model is built. The mathematical expressions for the steering performance indices are deduced and a stability criterion is established by integrated analysis of the vehicle's dynamics and the EPAS dynamics. By means of frequency domain analysis, the e ect of each parameter of EPAS on steering performance indices is analysed. Finally, an optimizing model used to improve these steering indices is put forward and the result is given.

In this paper, a dynamic model on a rigid rotor-sliding bearing system with a SFD is established. The stability and bifurcation behaviors of the system are studied. On the basis of the differential equations of fluid momentum and mass continuity, the distribution pressure function is derived by taking oil film inertia force into consideration. Damping force, clearance excitation force, interference force of different frequencies and static load are also considered in the model. Finally, the governing equations of the stability and bifurcation behaviors of the system are solved by Floquet theory. Simulation of dynamic model shows that the rigid rotor-sliding bearing system can maintain stability and exhibit a Hopf bifurcation phenomenon in a certain range.

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Abstract： Based on the statistical model for the tensile statistical strength of unidirectional composite materials and the stress analysis of 3-D braided composites, a new method is proposed to calculate the tensile statistical strength of the 3-D braided composites. With this method, the strength of 3-D braided composites can be calculated with very large accuracy, and the statistical parameters of 3-D braided composites can be determined. The numerical result shows that the tensile statistical strength of 3-D braided composites can be predicted using this method. Some researches have been reported [1] about stiffness and elastic constant of 3-D braided composites. Compared with the stiffness problem, strength problem of 3-D braided composites is more complex. There are two main reasons: firstly, the global properties of 3-D braided composite are more complicated than laminates, so these methods are not adopted directly to 3-D braided composites; secondly, the strength of composites is a complex statistical mechanics problem concerning situ characteristic, synergism effect, lamination effect, random bug, etc [2,3] , so that the traditional strength theory is very difficult to be adopted to composites. In order to satisfactorily analyze the failure and damage of 3-D braided composites, it is necessary to adopt statistical micro-mechanics to overcome the drawback of traditional strength theory.The structure of 3-D braided composites is a unitary three-directional space structure composed of interlacing fibers. Fibers and matrix materials of 3-D braided composites are tightly kinky unlike unidirectional composites and cross-ply laminates with the obvious interface effect between fiber and matrix. According to the fatigue test of 3-D braided composites by Tang et al [4] , in the course of the damage of 3-D braided composites, the damage of fiber and bundle is the principal effect. This shows the different failure models between 3-D braided composites and laminates, so the strength prediction methods based on the random critical-core probability model about unidirectional composites and cross-ply laminates can not be adapted to 3-D braided composites. Up to now, there is no report about the statistical strength analysis of 3-D