Industrial grinding processes always involve multiple sequential passes, such as rough, semi-rough, semi-finish, finish, and spark-out, for the surface and geometrical accuracy generation. The design of multi-pass grinding process parameters usually requires in-depth heuristic knowledge or complex process modeling. However, when multiple process output objectives must be achieved, either heuristic knowledge or analytical modeling is incapable in dealing with the large number of process parameters or decoupling the dependency of individual pass with its neighboring passes. In this paper, a hybrid Non-dominated Sorting Firefly Algorithm (NSFA) is proposed by incorporating the non-dominated sorting algorithm with the firefly algorithm. The developed NSFA is capable in searching the optimal whole set of grinding process parameters at improved convergence speed and with less iterations, which is proved by comparing with Non-dominated Genetic Algorithm (NSGA-II) and Nondominated Particle Swarm Optimization (NSPSO). Finally, a variable-pass internal grinding for engineering ceramics is carried out to verify the efficacy of the proposed NSFA. With the process output objectives of minimal grinding time and geometric error, the optimized process by the NSFA can realize the achievement of all process quality objectives simultaneously with the grinding efficiency increased by 32.4%. Keywords Hybrid Firefly Algorithm• Non-dominated sorting • Multi-pass grinding • Process optimization List of Symbols T Total grinding time n Total number of passes d 0 , d f Initial and final diameter d err or Diameter error of final product c 0 , c f Initial and final cylindricity r 0 , r f Initial and final roundness Ra 0 , Ra f Initial and final roundness B Xuekun Li
The perovskite crystal structure determines the appearance of ferroelectricity and the determination of the polarization direction of ferroelectric ceramics. When the polarization direction has a certain order, different domain structures will combine to form a multiparticle system with a specific morphology, the topological structures that exist in ferroelectrics. In this study, the domain structure of potassium sodium niobate (<em>K</em><sub>0.5</sub><em>Na</em><sub>0.5</sub><em>NbO</em><sub>3</sub>) thin films under different hysteresis electric fields and thicknesses was observed by the phase field method. According to the different switching paths of the domain structure under the electric field, the domain is divided into fast and slow switching process. Based on this, a method is proposed to first determine the domain switching state of the desired experiment and then conduct directional observation. Through the analysis of the domain structures combined with the polarization vector, a clear multi-domain combined vortex-antivortex pair topological structure was observed for the first time in <em>K</em><sub>0.5</sub><em>Na</em><sub>0.5</sub><em>NbO</em><sub>3</sub> films. The vortex structure was further analyzed for its switching process, and it was observed that this vortex topological microstructure can make the domain more likely to switch, so that more small-scale polarization vectors can be ordered to form the desired multiparticle system topology. This polarization vector ordering is similar to the microscopic phase boundary formed by the specific polarization directions on both sides of the morphotropic phase boundary (MPB) for the improvement of the dielectric properties of ferroelectric materials.
In this work, atomically K1−xNaxNbO3 thin films are taken as examples to investigate the reversible and irreversible effects in a horizon plane, i.e., the changes of domain structures, phase states, free energies, etc., under a z-axis alternating current field via a phase-field method. The simulation results show the driving forces during the charging and discharging process, where there is a variation for the angles of the domain walls from 180° to 90° (and then an increase to 135°), which are the external electric field and domain wall evolution, respectively. As for the phase states, there is a transformation between the orthorhombic and rhombohedral phases which can’t be explained by the traditional polarization switching theory. This work provides a reasonable understanding of the alternating current field effect, which is essential in information and energy storage.
Indentation techniques are usually simple and effective methods to characterize ceramics properties. This article establishes a numerical model of Vickers indentation by using the general exponent Drucker-Prager model, which is suitable for materials whose compressive yield strength is much higher than tensile strength. In addition, a standard method for calculating the diagonal length of indentation is also proposed. Using this FE model, several numerical simulations of Vickers indentation process are conducted. Then, through measuring the indentation morphology with the proposed method, the Vickers hardness is calculated, which has excellent agreement with the experiment results. The comparison results of simulation and experiment show that the proposed numerical model is robust and effective. It is very promising in modeling the indentation process.
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