Through qualitative and quantitative analysis of the specimens hydroextruded, we explore the effecis of the technology parameters on the rules of the metal-flow deformation. Visioplasticity method is applied to numerical analysis of tubes(or rods). Based on the results of numerical analysis, it is noticed that there is considerable tensile strain in the inner wall of the billet near the inner side of the outlet of the die. The place and the form of fractures are discussed. In analysing some groups of specimens with variable parameters, different materials and different heat-treatment techniques are used. It should be pointed out here that rules of axisymmetric laminal flow of metallic billets hydroextruded are dependent upon the material and mechanical boundary conditions. Such flow rules have influenced not only the stress fields of the deformation zone of billet, but also the distribution of residual stresses of the tube. The optimization of the parameters is also discussed. 相似文献
This paper studies an approximate continuous fixed-time terminal sliding mode control (CFTSMC) with prescribed performance for uncertain robotic manipulators. A transformation concerning tracking error using a fixed-time prescribed performance function is proposed to guarantee the transient and steady-state performance of trajectory tracking control for uncertain robotic manipulators within fixed time. Utilizing the transformed error, a smooth fixed-time sliding mode surface is designed. Then, based on the proposed sliding mode surface, an approximate CFTSMC scheme is presented to achieve inherent chattering-free control for uncertain robotic manipulators. According to the Lyapunov stability theory, it is proved that the position tracking error can be bounded in the prescribed performance boundaries and globally converges to a defined small region within fixed time and then approaches exponentially to the origin. Several numerical simulation results demonstrate the effectiveness and superiority of the proposed control strategy for uncertain robotic manipulators.