Numerical simulation for machining S-tube by abrasive flow with various particle volume fractions

Abrasive flow machining has become an economical and efficient ultra-precision process for machining complex-shaped pipe parts, and processing effect is exceedingly subject to particle volume fraction. In this paper, aiming at uncovering the influence of various particle volume fractions on the machining result of abrasive flow finishing, based on fluid mechanics theory, mixed phase model and discrete phase model were conducted, FLUENT software was resorted to simulate the numerical characteristics of the solid-liquid two-phase flow field in the inner channel of S-tube with different-particle-volume-fraction abrasive flows, the mechanism of erosion and wear of particles was uncovered, which provides a theoretical basis for abrasive flow machining S-tube structured components

A Mandrel Feeding Strategy in Conical Ring Rolling Process

A mathematical model for radial conical ring rolling with a closed die structure on the top and bottom of driven roll, simplified as RCRRCDS, was established. The plastic penetration and biting-in conditions in RCRRCDS process were determined. A mandrel feeding strategy for RCRRCDS process was proposed. The mandrel feed rate and its reasonable value range were deduced. The coupled thermal-mechanical FE model of RCRRCDS process was established. The reasonable value range of the mandrel feed rate was verified by using numerical simulation method. The results indicate that the reasonable value range of the mandrel feed rate is feasible, the proposed mandrel feeding strategy can realize a steady RCRRCDS process, and the forming quality of conical ring rolled by using the proposed feeding strategy is better than that of conical ring rolled by using a constant mandrel feed rate

The Effects of Forming Parameters on Conical Ring Rolling Process

The plastic penetration condition and biting-in condition of a radial conical ring rolling process with a closed die structure on the top and bottom of driven roll, simplified as RCRRCDS, were established. The reasonable value range of mandrel feed rate in rolling process was deduced. A coupled thermomechanical 3D FE model of RCRRCDS process was established. The changing laws of equivalent plastic strain (PEEQ) and temperature distributions with rolling time were investigated. The effects of ring’s outer radius growth rate and rolls sizes on the uniformities of PEEQ and temperature distributions, average rolling force, and average rolling moment were studied. The results indicate that the PEEQ at the inner layer and outer layer of rolled ring are larger than that at the middle layer of ring; the temperatures at the “obtuse angle zone” of ring’s cross-section are higher than those at “acute angle zone”; the temperature at the central part of ring is higher than that at the middle part of ring’s outer surfaces. As the ring’s outer radius growth rate increases at its reasonable value ranges, the uniformities of PEEQ and temperature distributions increase. Finally, the optimal values of the ring’s outer radius growth rate and rolls sizes were obtained

Giant photoinduced lattice distortion in oxygen-vacancy ordered SrCoO2.5 thin films

Despite of the tremendous efforts spent on the oxygen vacancy migration in determining the property optimization of oxygen-vacancy enrichment transition metal oxides, few has focused on their dynamic behaviors non-equilibrium states. In this work, we performed multi-timescale ultrafast X-ray diffraction measurements by using picosecond synchrotron X-ray pulses and femtosecond table-top X-ray pulses to monitor the structural dynamics in the oxygen-vacancy ordered SrCoO2.5 thin films. A giant photoinduced strain ({\Delta}c/c > 1%) was observed, whose distinct correlation with the pump photon energy indicates a non-thermal origin of the photoinduced strain. The sub-picosecond resolution X-ray diffraction reveals the formation and propagation of the coherent acoustic phonons inside the film. We also simulate the effect of photoexcited electron-hole pairs and the resulting lattice changes using the Density Function Theory method to obtain further insight on the microscopic mechanism of the measured photostriction effect. Comparable photostrictive responses and the strong dependence on excitation wavelength are predicted, revealing a bonding to anti-bonding charge transfer or high spin to intermediate spin crossover induced lattice expansion in the oxygen-vacancy films.Comment: 12 pages, 4 figures, support materia