Papers by Keyword: Mixed Control

Abstract: Conditions are obtained for unique solution existence of a mixed control problem without taking in account control expenses for a system that described by an initial-boundary value problem for the linearized quasi-stationary system of phase field equations. The problem is reduced to an optimal control problem for operator differential equation of first order in abstract space with degenerate operator at derivative using start and distributed controls simultaneously. The theorem on the unique solvability of this problem is applied to studying of optimal control problem for the phase field equations system.

Abstract: Pseudo-dynamic testing using force- mixed control strategy is presented for structures with large stiffness. In this proposed method, the displacement response of the specimen measured by a linear variable displacement transducer with higher resolution than that in the actuator is fed back. A proportional-integral controller is adopted in the outer displacement control loop, and a coefficient CF is employed to convert the displacement to force command. Numerical and experimental validations show that this method exhibits excellent performance in terms of stability and accuracy if proper controller parameters are adopted and is superior to the conventional displacement control method for large-stiffness structures.

Abstract: A mixed control mode is developed to model the ledge growth of pro-eutectoid ferrite, considering coupled effects of migration of austenite/ferrite interface and carbon diffusion in austenite. Carbon concentration of austenite at the austenite/ferrite interface increases from the bulk carbon concentration to a steady level, which is lower than that in local equilibrium, during the ferrite growth process. Correspondingly, ferrite grows rapidly at the beginning since all the driving force of ferrite transformation is dissipated on the interface migration. In the later stage of isothermal transformation, the growth rate of ferrite decreases towards a steady level since a part of driving force is dissipated on carbon diffusion in austenite. The effect of interface migration on ferrite growth rate by changing the interface mobility is emphatically discussed. In the case of the low interface mobility, the growth rate of ferrite is very small while the growth is dominated by the carbon diffusion ability in the case of large interface mobility. When a medium interface mobility is obtained, the growth rate of ferrite may reach a maximum value, which exceed the limitation of diffusion control and interface control modes. After comparing the modeled growth rate of ferrite with the experimental data of 0.11-0.49 wt% C alloy at 973-1113 K, the pre-expontential factor (M₀) of interface mobility is estimated within the range of 0.1-1 mol m J^-1 s^-1, around the value 0.5 mol m J^-1 s^-1 theoretically estimated.

Abstract: More than twenty years were needed for people to understand the formation mechanism of the periodic-layered structures not only because of the complications of pattern formation, but also due to the limits of traditional diffusion theories. Based on the general theory of interdiffusion growth proposed by Y.C. Chen et al. [1], the quantitative model of periodic layer formation during solid state reactions has been succeeded [2]. The experimental results shown in this paper proved one of the model’s predicts that the reactive diffusion system Zn/Fe3Si with clamp press annealed at 663K should be mixed controlled. Also, the important influence of the uniaxial compressive stress on the diffusion coefficient was emphasized and the reasons are discussed.