Evolution mechanism of microstructure and microhardness of Ti–6Al–4V alloy during ultrasonic elliptical vibration assisted ultra-precise cutting

The ultra-precision Ti–6Al–4V alloy parts are growing used in medical and aerospace industries, and which always work in the extreme working conditions such as high temperature, high pressure, and variable load. Thus, the requirements for machining accuracy and surface quality of parts are getting higher and higher. The ultrasonic elliptical vibration assisted cutting (UEVC) technology has been proved to be an effective method for the ultra-precision machining of Ti–6Al–4V alloy. However, in the UEVC process, the evolution mechanism of microstructure and microhardness, which directly affect the service performance and life, is unrevealed. In this paper, the comprehensive investigations of microstructural plastic deformation, grain refinement, phase transformation and microhardness of machined surface layer under conventional cutting (CC) and UEVC processes are carried out. The experimental results indicated that, due to the effects of UEVC technology, the plastic deformation area show obvious compression deformation, the depth of plastic deformation is less than 10 μm, there is no obvious phase transformation on the machined surface layer material, and the hardening rate of machined surface is more than 20%. These findings show the UEVC technology has a unique influence on the microstructure and microhardness of Ti–6Al–4V alloy, which have important implications for the cutting parameter design of ultra-precision Ti–6Al–4V alloy parts

Design and test of urea hydrolysis reactor for vehicle

Ammonia production technology of urea-SCR system for vehicle is mainly used in pyrolysis. The reaction is complex, and there are some side effects. So a kind of urea hydrolysis device for vehicle is designed. Based on the in-depth analysis of ammonia production technology’s mechanism of urea hydrolysis for vehicle, the modified extended UNIQUAC equation and PHS equation of state were used to solve the thermodynamic model, and the experimental verification was carried out on the JX493ZLQ3 diesel engine. The results show that the design of urea hydrolysis reactor is in agreement with the experimental results. In the environment of urea hydrolysis, the higher the hydrolysis temperature, the faster the urea hydrolysis and the faster the production of ammonia. Under the same conditions, the hydrolysis rate of urea was the same, the higher the initial quality, the more ammonia produced. The method is suitable for the ammonia production technology of urea hydrolysis for vehicle and can be used for the formation of urea hydrolysis SCR system

Design and test of urea hydrolysis reactor for vehicle

Ammonia production technology of urea-SCR system for vehicle is mainly used in pyrolysis. The reaction is complex, and there are some side effects. So a kind of urea hydrolysis device for vehicle is designed. Based on the in-depth analysis of ammonia production technology’s mechanism of urea hydrolysis for vehicle, the modified extended UNIQUAC equation and PHS equation of state were used to solve the thermodynamic model, and the experimental verification was carried out on the JX493ZLQ3 diesel engine. The results show that the design of urea hydrolysis reactor is in agreement with the experimental results. In the environment of urea hydrolysis, the higher the hydrolysis temperature, the faster the urea hydrolysis and the faster the production of ammonia. Under the same conditions, the hydrolysis rate of urea was the same, the higher the initial quality, the more ammonia produced. The method is suitable for the ammonia production technology of urea hydrolysis for vehicle and can be used for the formation of urea hydrolysis SCR system

Study of Flexural Response in Strain Hardening Cementitious Composites Based on Proposed Parametric Model

Strain hardening cementitious composites (SHCCs) are widely used in projects due to their excellent deformation resistance and large energy absorption capacity. However, determining tensile strain capacity is still a challenge for engineers. The current popular approach is to use inverse methods to predict the tensile behavior of SHCCs, such as the UM method (Qian and Li) and the JCI (Japan Concrete Institute) method. The key to these two approaches is to acquire the exact relationship between the bending and the uniaxial response. In this paper, a reasonable linear constitutive model of the SHCCs is modified. Initially, the moment-curvature diagrams are discussed by material parameters. The results reveal that the moment-curvature response is quite sensitive to the variations in the parameter of transition strain α, post-cracking tensile stiffness η, and strain softening stiffness μ, however, for the compressive parameters, the moment-curvature responses influence on flexural behavior is insignificant. Moreover, the load-deflection curve in the mid-span of SHCC, based on the consideration of shear effect, is simulated under a four-point bending test (FPBT). The results show a remarkable consistency with the experimental data when compared to the previous simulations. It is expected that this modified method can enhance an accurate program in order to obtain the tensile capacity

Effect of Different Silane Coupling Agents In-Situ Modified Sepiolite on the Structure and Properties of Natural Rubber Composites Prepared by Latex Compounding Method

With the increasing demand for eco-friendly, non-petroleum-based natural rubber (NR) products, sepiolite, a naturally abundant, one-dimensional clay mineral, has been identified as a suitable material for reinforcing NR through the latex compounding method. To create superior NR/sepiolite composites, three silane coupling agents with different functional groups were used to modify sepiolite in situ via grafting or adsorption during the disaggregation and activation of natural sepiolite, which were subsequently mixed with natural rubber latex (NRL) to prepare the composites. The results showed that the modified sepiolite improved the dispersion and interfacial bonding strength with the rubber matrix. VTES-modified sepiolite containing C=C groups slightly improved the performance but retarded the vulcanization of the NR composites, and MPTES and TESPT-modified sepiolites containing -SH and −S4− groups, respectively, effectively accelerated vulcanization, inducing the composites to form a denser crosslink network structure, and exhibiting excellent dynamic and static properties, such as the modulus at a 300% increase from 8.82 MPa to 16.87 MPa, a tear strength increase from 49.6 N·mm−1 to 60.3 N·mm−1, as well as an improved rolling resistance and abrasive resistance of the composites. These findings demonstrate that modified sepiolite can be used to produce high-quality NR/sepiolite composites with enhanced properties

A Comparison of Three Sediment Acoustic Models Using Bayesian Inversion and Model Selection Techniques

Many geoacoustic models are used to establish the relationship between the physical and acoustic properties of sediments. In this work, Bayesian inversion and model selection techniques are applied to compare combinations of three geoacoustic models and corresponding scattering models—the fluid model with the effective density fluid model (EDFM), the grain-shearing elastic model with the viscosity grain-shearing (VGS(λ)) model, and the poroelastic model with the corrected and reparametrized extended Biot–Stoll (CREB) model. First, the resolution and correlation of parameters for the three models are compared based on estimates of the posterior probability distributions (PPDs), which are obtained by Bayesian inversion using the backscattering strength data. Then, model comparison and selection techniques are utilized to assess the matching degree of model predictions and measurements qualitatively and to ascertain the Bayes factors in favor of each quantitatively. These studies indicate that the fluid and poroelastic models outperform the grain-shearing elastic model, in terms of both parameter resolution and the ability to produce predictions in agreement with measurements for sandy sediments. The poroelastic model is considered to be the best, as the inversion based on it can provide more highly resolved information of sandy sediments. Finally, the attempt to implement geoacoustic inversion with different models provides a relatively feasible remote sensing scheme for various types of sediments under unknown conditions, which needs further validation

Effects of non-sinusoidal pitching motion on the propulsion performance of an oscillating foil.

Numerical simulations have been used in this paper to study the propulsion device of a wave glider based on an oscillating hydrofoil, in which the profile of the pitching and heaving motion have been prescribed for the sake of simplicity. A grid model for a two-dimensional NACA0012 hydrofoil was built by using the dynamic and moving mesh technology of the Computational Fluid Dynamics (CFD) software FLUENT and the corresponding mathematical model has also been established. First, for the sinusoidal pitching, the effects of the pitching amplitude and the reduced frequency were investigated. As the reduced frequency increased, both the mean output power coefficient and the optimal pitching amplitude increased. Then non-sinusoidal pitching was studied, with a gradual change from a sinusoid to a square wave as the value of β was increased from 1. It was found that when the pitching amplitude was small, the trapezoidal pitching profile could indeed improve the mean output power coefficient of the flapping foil. However, when the pitching amplitude was larger than the optimal value, the non-sinusoidal pitching motion negatively contributed to the propulsion performance. Finally, the overall results suggested that a trapezoidal-like pitching profile was effective for the oscillating foil of a wave glider when the pitching amplitude was less than the optimal value

Propulsion Performance of the Full-Active Flapping Foil in Time-Varying Freestream

A numerical investigation of the propulsion performance and hydrodynamic characters of the full-active flapping foil under time-varying freestream is conducted. The finite volume method is used to calculate the unsteady Reynolds averaged Navier–Stokes by commercial Computational Fluid Dynamics (CFD) software Fluent. A mesh of two-dimensional (2D) NACA0012 foil with the Reynolds number Re = 42,000 is used in all simulations. We first investigate the propulsion performance of the flapping foil in the parameter space of reduced frequency and pitching amplitude at a uniform flow velocity. We define the time-varying freestream as a superposition of steady flow and sinusoidal pulsating flow. Then, we study the influence of time-varying flow velocity on the propulsion performance of flapping foil and note that the influence of the time-varying flow is time dependent. For one period, we find that the oscillating amplitude and the oscillating frequency coefficient of the time-varying flow have a significant influence on the propulsion performance of the flapping foil. The influence of the time-varying flow is related to the motion parameters (reduced frequency and pitching amplitude) of the flapping foil. The larger the motion parameters, the more significant the impact of propulsion performance of the flapping foil. For multiple periods, we note that the time-varying freestream has little effect on the propulsion performance of the full-active flapping foil at different pitching amplitudes and reduced frequency. In summary, we conclude that the time-varying incoming flow has little effect on the flapping propulsion performance for multiple periods. We can simplify the time-varying flow to a steady flow field to a certain extent for numerical simulation