Jinjun Wu

Rapid pressure unloading is essential for the back pressure assembly of injector test systems. In this study, a high-speed unloading valve was developed for the back pressure assembly of an injector test system, and its pressure unloading characteristics were investigated through coupled numerical simulation and experimental testing. An electromagnetic–mechanical–fluid coupled dynamic model was established to describe the interactions among electromagnetic actuation, valve core motion, and hydraulic forces. Three-dimensional CFD simulations were performed to investigate the steady flow and hydraulic-force characteristics, followed by a two-dimensional transient model for analyzing the hydraulic force during valve closure. A coupled Simulink–AMESim model was then established to evaluate the system-level pressure unloading response and compared with experimental measurements under several initial pressure conditions. The CFD results reproduced the variation in flow rate with pressure differential, while sensitivity and uncertainty analyses showed that the quantified factors could not fully account for the discrepancy in absolute flow rate. Three-dimensional CFD revealed both axial and radial hydraulic forces, while 2D–3D comparison supported the use of the two-dimensional model for transient axial-force analysis. The system-level simulation and experimental results exhibited comparable pressure unloading characteristics within the investigated operating range.

To delineate admissible operating conditions of hydrostatic guideways under coupled multi-degree-of-freedom pose variations, a deterministic pose space envelope based on geometric contact and vertical-stiffness performance criteria was developed. The geometric lower boundary represents the onset of asperity interference, whereas the stiffness upper boundary represents a prescribed minimum vertical stiffness and is therefore a performance limit rather than a physical failure limit. Their intersection defines the allowable pose range and central-clearance interval for a prescribed parameter set. The geometric boundary exhibits a symmetric inverted quadrangular-pyramidal shape, while the stiffness boundary forms a smooth dome. Numerical comparisons for an HS50-130 slider at three representative poses gave a maximum relative difference of 3.68% in the individual critical clearances. The method supports operating-limit warning, parameter optimization, and deterministic margin evaluation within the investigated small-angle, quasi-steady scope.

To enhance the aerodynamic performance of Ti6Al4V functional components, this paper systematically investigated the femtosecond laser processing technology for surface drag-reduction microstructures, aiming to fabricate high-performance microstructures. (1) V-shaped, U-shaped, and rectangular micro-grooves were designed based on the boundary layer theory, and their drag-reduction mechanisms were elucidated through CFD numerical simulations. The results indicate that the V-shaped groove achieves a peak drag-reduction rate of 13.1% at a dimensionless depth of h⁺ = 15 and an aspect ratio of 1, primarily due to the formation of a low-velocity zone and the suppression of turbulent bursts by secondary vortices. (2) Through single-factor experiments, the influence laws of femtosecond laser process parameters on the V-shaped groove were explored. (3) Regression prediction models for groove dimensions were established using the Response Surface Methodology (RSM) to optimize the processing parameters. Under the optimized conditions, high-quality V-shaped groove arrays with a width of 55.9 μm and a depth of 55.5 μm were successfully fabricated on the Ti6Al4V surface, characterized by high consistency and a minimal heat-affected zone. This research provides an effective technical solution for the precision manufacturing of high-performance drag-reduction structures on titanium alloy surfaces.

The demand for miniaturized high-temperature components necessitates advanced additive manufacturing techniques, yet the microstructural and mechanical consequences of scaling down the laser powder bed fusion (LPBF) process remain poorly understood. In this study, we systematically investigate the scaling effects of micro laser powder bed fusion (μ-LPBF) versus conventional LPBF on the phase transformation kinetics and performance of the near-α Ti65 alloy. Results demonstrate that μ-LPBF significantly enhances surface integrity, reducing the arithmetic mean roughness (Ra) by 59.5%. Microstructural characterization reveals that the extreme cooling rates intrinsic to the microscale melt pool induce a massive refinement of hierarchical α′ martensite and promote a highly randomized variant selection. Consequently, the strong building-direction crystallographic texture typical of LPBF is substantially weakened, and the proportion of high-angle grain boundaries increases to 91.6%. This microstructural homogenization effectively mitigates mechanical anisotropy, reducing the directional variance in the Schmid factor by 35%. In terms of mechanical properties, μ-LPBF demonstrates exceptional strengthening at both room temperature and 600 °C, achieving a room-temperature yield strength of 1297 MPa and an ultimate tensile strength of 1514 MPa, which represent increases of 16.5% and 8.6%, respectively, compared to those of conventional LPBF. These findings provide critical insights into defect suppression and multiscale microstructural control under extreme thermal gradients, paving the way for the fabrication of isotropic, high-strength micro devices.

Ti65 high-temperature titanium alloy, known for its exceptional high-temperature mechanical properties and oxidation resistance, demonstrates considerable potential for aerospace applications. Nevertheless, conventional manufacturing techniques are often inadequate for achieving high design freedom and fabricating complex geometries. This study presents a systematic investigation into the process optimization, microstructure characterization, and mechanical performance of Ti65 alloy produced by laser powder bed fusion (LPBF). Via meticulously designed single-track, multi-track, and bulk sample experiments, the influences of laser power (P), scanning speed (V), and hatch spacing (h) on molten pool behavior, defect formation, microstructural evolution, and surface roughness were thoroughly examined. The results indicate that under optimized parameters, the specimens attain ultra-high dimensional accuracy, with a near-full density (>99.99%) and reduced surface roughness (Ra = 3.9 ± 1.3 μm). Inadequate energy input (low P or high V) led to lack-of-fusion defects, whereas excessive energy (high P or low V) resulted in keyhole porosity. Microstructural analysis revealed that the rapid solidification inherent to LPBF promotes the formation of fine acicular α′-phase (0.236–0.274 μm), while elevated laser power or reduced scanning speed facilitated the development of coarse lamellar α′-martensite (0.525–0.645 μm). Tensile tests demonstrated that samples produced under the optimized parameters exhibit high ultimate tensile strength (1489 ± 7.5 MPa), yield strength (1278 ± 5.2 MPa), and satisfactory elongation (5.7 ± 0.15%), alongside elevated microhardness (446.7 ± 1.7 HV_0.2). The optimized microstructure thereby enables the simultaneous achievement of high density and superior mechanical properties. The fundamental mechanism is attributed to precise control over volumetric energy density, which governs melt pool mode, defect generation, and solidification kinetics, thereby tailoring the resultant microstructure. This study offers valuable insights into defect suppression, microstructure control, and process optimization for LPBF-fabricated Ti65 alloy, facilitating its application in high-temperature structural components.

Unknown time-varying parameters, along with mismatched and matched disturbances, exist in hydraulic systems, worsening position tracking performance and even destabilizing systems. To address this issue, this article proposes an adaptive full-state prescribed performance position tracking control for hydraulic systems subject both to unknown time-varying parameters and to mismatched and matched disturbances. First, a smooth nonlinear term is skillfully introduced into the controller design so that it can simultaneously cope with both unknown time-varying parameters and disturbances. Next, by integrating the adaptive technique and the prescribed performance function, an adaptive full-state prescribed performance position tracking controller is developed for hydraulic systems in which both the transient and steady performance of all the control errors can be prescribed. A stability analysis then confirms both the prescribed transient performance and the asymptotic steady performance of all the control errors. Finally, the superiority of the proposed controller is also validated by comparison with simulation results.

The integrated braking control system (IBC) has become one of the most popular brake-by-wire (BBW) solutions due to its compactness and versatility. Accurate monitoring of wheel cylinder pressure in real time is the basis for brake pressure control, and pressure estimation is a low-cost and reliable method. However, the IBC is an electromechanical hydraulic coupling system that has significant nonlinear behaviors; moreover, vehicle dynamics also have a critical impact on the accuracy of pressure estimation. To solve this problem, this paper proposes a novel adaptive extended Kalman filter (EKF) approach that combines a hydraulic model and a single-wheel model. This novel strategy has better estimation than the hydraulic model when the pressure is accurately estimated by the single-wheel model, while when the single-wheel model is not accurate, the EKF degrades to the hydraulic model. Finally, vehicle experimental data under high- and low-mu braking are collected. The pressure estimation error of the EKF is within 0.4 MPa in the low-mu road and 2 MPa in the high-mu road. It is proven that the proposed pressure estimation strategy is highly effective.