The microstructure, mechanical properties and corrosion resistance of Zr-30%Ta and Zr-25%Ta-5%Ti alloy prepared by spark plasma sintering (SPS) technology were investigated. The experimental results showed that the Zr-Ta-Ti alloys made by the SPS processing have a low level of porosity with the relative density of 96%–98%. The analyses of XRD and TEM revealed that the Zr-30Ta alloy consists of α+β phase, and the Zr-25Ta-5Ti alloy belongs to the near β type alloy containing a small amount of α and ω phases. With the addition of Ti, the elastic modulus of the alloys was decreased from (99.5±7.2) GPa for Zr-30Ta alloy to (73.6±6.3) GPa for Zr-25Ta-5Ti alloy. Furthermore, it is shown that, in comparison to CP-Ti and Ti-6Al-4V alloy, the Zr-Ta-Ti alloy produced in this work offers an improved corrosion resistance due to the more stable ZrO2 and Ta2O5 generated in the passivation film on the surface of the alloys. This study demonstrates that Zr-Ta-Ti alloys are a promising candidate of novel metallic biomaterials.
Functionalized implants demonstrate an upgraded approach in orthopedic implants, aiming to achieve long term success through improved bio integration. Bioceramic coatings with multifunctionality have arisen as an effective substitute for conventional coatings, owing to their combination of various properties that are essential for bio-implants, such as osteointegration and antibacterial character. In the present study, thin hopeite coatings were produced by Pulsed laser deposition (PLD) and radio frequency magnetron sputtering (RFMS) on Ti64 substrates. The obtained hopeite coatings were annealed at 500 °C in ambient air and studied in terms of surface morphology, phase composition, surface roughness, adhesion strength, antibacterial efficacy, apatite forming ability, and surface wettability by scanning electron microscope (SEM), X-ray diffraction (XRD), atomic force microscope (AFM), tensometer, fluorescence-activated cell sorting (FACS), simulated body fluid (SBF) immersion test and contact angle goniometer, respectively. Furthermore, based on promising results obtained in the present work it can be summarized that the new generation multifunctional hopeite coating synthesized by two alternative new process routes of PLD and RFMS on Ti64 substrates, provides effective alternatives to conventional coatings, largely attributed to strong osteointegration and antibacterial character of deposited hopeite coating ensuring the overall stability of metallic orthopedic implants.
Chrome steels are used in bearings since they possess high strength and wear resistance. However, when those parts are in service, failure happens due to sliding friction before the lifetime. To improve the durability of the American Iron and Steel Institute (AISI) 52100 chromium steel, in this work, the effect of laser surface texturing (LST) was analyzed. With the different patterns of circle and ellipse comparing with the untextured samples, the wear behavior was investigated using the pin-on-disc tribometer. The lubricant used for wear analysis is semisolid lithium grease National Lubricating Grease Institute lubricant (SKF NLGI-3). Sliding wear analysis was conducted at different loads of 10 N, 30 N and 50 N for the sliding speed of 750 r/min and 1400 r/min. The wear morphology was analyzed using a scanning electron microscope(SEM). The roughness of the samples was found using a white light interferometer. The effect of different patterns like circle and ellipse, alter the friction and wear properties of chromium alloy was observed compared with the untextured samples. LST shows considerable reduction in friction and wear for ellipsoidal pattern compared with the circular pattern because of wear debris and lubricant getting trapped.
Implementation of manganese-bismuth (MnBi) alloys as high-performance permanent magnets is a challenge for physicists and engineers because the ferromagnetic low-temperature phase (LTP) is not exclusively obtained. In this work, melting powered by four commercial magnetrons of 2000–2500 W in a microwave furnace is demonstrated as a new route to alloy MnBi. Under an argon atmosphere, microwave heating transferred to pieces of broken Bi ingots and Mn flakes for 2 h gave rise to products of inhomogeneous composition and morphology. Scanning electron micrographs were classified into three regions according to morphology and elemental composition. Cubic-like clusters characterized as Mn precipitated over light solidified Bi-rich regions, and the MnBi phase was formed in homogeneous regions with a balanced composition between Mn and Bi. A ferromagnetic hysteresis loop was obtained in the ground powder with a coercivity of 40 kA/m. Subsequent annealing at 553 K under a pressure of 414 kPa for 12 h enhanced the MnBi phase with extended regions of balanced composition. It follows that the coercivity was increased to 60 kA/m. However, remanent magnetization was slightly reduced. This MnBi alloyed by microwave radiation can be further used in rare-earth-free magnets.
Ultra-large plate forgings are foundation of heavy machinery, but many parts of the type cannot be made by conventional technologies due to the characters of extreme manufacturing in terms of size and quality requirements. This paper introduced a systematically method called cylinder unfolding method (CUM) for producing large plate forgings, by using a serial of operations including “splitting”, “unfolding”, and “flattening” of a thick cylinder obtained from saddle forging. The technological route of CUM was presented in detail with an example of plate forging with the horizontal sizes of 6100 mm and thickness of 300 mm. The deformation features of saddle forging for fabricating transitional cylinders were analyzed, and then the subsequent handling steps including splitting, unfolding and flattening of the cylinder, as well as the auxiliary processing, were addressed. The practice proved that CUM can provide an efficient way for manufacturing ultra-large plate forgings and meet the strict requirements in geometry and mechanical performance, without highly increasing the investments of forming equipment and tooling.
This study reports the investigations for repair of thermoplastic based automotive bumpers and bars with modified friction stir welding (MFSW) process. For MFSW, consumable tool of polyamide6 (PA6) composite has been used for joining of acrylonitrile butadiene styrene (ABS) composites. The dissimilar thermoplastics were processed for maintaining a useful range of melt flow properties followed by preparation of feed stock filament for fused deposition modeling (FDM) process through screw extrusion. Finally, 3D printed PA6 based consumable rapid tool (RT) was prepared for MFSW. The joints prepared were subjected to flexural, hardness, morphological and thermal testing. The study has suggested the that maximum mechanical strength was obtained for sample welded at 1400 r/min, 50 mm/min transverse speed and 3 mm plunge depth, whereas the minimum mechanical strength was obtained for sample welded at 1000 r/min, 30 mm/min transverse speed and 2 mm plunge depth. The results are also supported with thermal analysis and photomicrographs.
Approximately 2.0–3.0 t of copper slag (CS) containing 35%–45% iron is generated for every ton of copper produced during the pyrometallurgical process from copper concentrate. Therefore, the recovery of iron from CS utilizes a valuable metal and alleviates the environmental stress caused by stockpile. In this paper, a new method has been developed to realize the enrichment of iron in CS through the selective removal of silica. The thermodynamic analyses and experimental results show that the iron in CS can be fully reduced into metallic iron by carbothermic reduction at 1473 K for 60 min. The silica was converted into free quartz solid solution (QSS) and cristobalite solid solution (CSS). QSS and CSS are readily soluble, whereas metallic iron is insoluble, in NaOH solution. Under optimal leaching conditions, a residue containing 87.32% iron is obtained by decreasing the silica content to 6.02% in the reduction roasted product. The zinc content in the residue is less than 0.05%. This study lays the foundation for the development of a new method to comprehensively extract silicon and iron in CS while avoiding the generation of secondary tailing.
Before-after study with the empirical Bayes (EB) method is the state-of-the-art approach for estimating crash modification factors (CMFs). The EB method not only addresses the regression-to-the-mean bias, but also improves accuracy. However, the performance of the CMFs derived from the EB method has never been fully investigated. This study aims to examine the accuracy of CMFs estimated with the EB method. Artificial realistic data (ARD) and real crash data are used to evaluate the CMFs. The results indicate that: 1) The CMFs derived from the EB before-after method are nearly the same as the true values. 2) The estimated CMF standard errors do not reflect the true values. The estimation remains at the same level regardless of the pre-assumed CMF standard error. The EB before-after study is not sensitive to the variation of CMF among sites. 3) The analyses with real-world traffic and crash data with a dummy treatment indicate that the EB method tends to underestimate the standard error of the CMF. Safety researchers should recognize that the CMF variance may be biased when evaluating safety effectiveness by the EB method. It is necessary to revisit the algorithm for estimating CMF variance with the EB method.
Focusing on data imbalance and intraclass variation, an improved pedestrian detection with a cascade of complex peer AdaBoost classifiers is proposed. The series of the AdaBoost classifiers are learned greedily, along with negative example mining. The complexity of classifiers in the cascade is not limited, so more negative examples are used for training. Furthermore, the cascade becomes an ensemble of strong peer classifiers, which treats intraclass variation. To locally train the AdaBoost classifiers with a high detection rate, a refining strategy is used to discard the hardest negative training examples rather than decreasing their thresholds. Using the aggregate channel feature (ACF), the method achieves miss rates of 35% and 14% on the Caltech pedestrian benchmark and Inria pedestrian dataset, respectively, which are lower than that of increasingly complex AdaBoost classifiers, i.e., 44% and 17%, respectively. Using deep features extracted by the region proposal network (RPN), the method achieves a miss rate of 10.06% on the Caltech pedestrian benchmark, which is also lower than 10.53% from the increasingly complex cascade. This study shows that the proposed method can use more negative examples to train the pedestrian detector. It outperforms the existing cascade of increasingly complex classifiers.
Planet gear systems (PGSs) are key components of transmission mechanisms. Structural and material characteristics of gearbox and shaft can affect the support stiffness and vibrations of PGSs. The ring gear flexibility should affect the vibrations of PGSs too. However, most previous work did not completely consider the effects of the ring gear flexibility on the vibrations of PGSs and flexible supports of ring and sun gears. Thus, this paper presents a flexible-rigid coupling multi-body dynamic (FMBD) model for a PGS with the flexible supports and ring gear flexibility. A finite element model of ring gear is established to formulate the ring gear flexibility. The influences of clearance and damping of planet bearings on the vibrations of PGS are considered. The effects of flexible supports and ring gear flexibility on the vibrations of PGS under different moment and speed conditions are studied. The statistical parameters and peak frequencies of PGS from the proposed FMBD and previous rigid multi-body dynamic (RMBD) models are compared. The results denote that the flexible support has a great effect on the vibrations of PGS. This paper can provide some guidance for the support structure design and vibration control for PGSs.
Condition assessment is one of the most significant techniques of the equipment’s health management. Also, in PHM methodology cycle, which is a developed form of CBM, condition assessment is the most important step of this cycle. In this paper, the remaining useful life of the equipment is calculated using the combination of sensor information, determination of degradation state and forecasting the proposed health index. The combination of sensor information has been carried out using a new approach to determining the probabilities in the Dempster-Shafer combination rules and fuzzy c-means clustering method. Using the simulation and forecasting of extracted vibration-based health index by autoregressive Markov regime switching (ARMRS) method, final health state is determined and the remaining useful life (RUL) is estimated. In order to evaluate the model, sensor data provided by FEMTO-ST Institute have been used.
The topography of gear meshing interfaces is one of the key factors affecting the dynamic characteristics of the gear transmission system. In order to obtain the contact characteristics of meshing gear pair with different surface micro-topographies, an interface feature model and a tribo-dynamics coupling model for the gear system are proposed in this paper. The effects of the gear tooth surface micro-topography on the oil film distribution, contact damping and friction are considered. The time-varying meshing stiffness and the static transmission error are included in the abovementioned models. An exemplary gear pair is analyzed using the proposed models to investigate the influence of the surface micro-topography on the dynamic characteristics of gear system under different micro-topographies and input torque conditions. Simulation results show that the effects of gear tooth micro-topography on the gear dynamic responses (including the friction and the vicious damping at the gear meshing interface and the vibration in the direction of offline of action) are highly dependent on the regularity of tooth surface. The vibration and noise can be significantly controlled by manufacturing a regular gear tooth profiles instead of random profiles.
In this study, thermo-fluid characteristics of elliptical annular finned tube heat exchanger were numerically studied in detail. Transition SST model was utilized to simulate turbulent flow. Effects of air velocities, horizontal to vertical fin diameter ratios, and fin densities were examined in detail. The simulations indicate superior performance of elliptical fin layout. It was shown that pressure drop of annular elliptical fin can be only one half of that of a circular annular fin while containing comparable heat transfer performance. The vertical elliptical annular fin may even contain a higher heat transfer performance over circular fin. Correlations are proposed to estimate the Nu number and pressure drop based on the annular circular fin. The maximum deviations between the proposed correlations and simulations regarding pressure drop and heat transfer coefficient are 5.6% and 3.2%, respectively. For further elaboration of the superiority of the elliptical layout from the second law perspective, normalized entropy generation was also studied. In all cases, the entropy generation rate in circular fin was higher than that of an elliptical fin.
Aviation heavy-fuel spark ignition (SI) piston engines have been paid more and more attention in the area of small aviation. Aviation heavy-fuel refers to aviation kerosene or light diesel fuel, which is safer to use and store compared to gasoline fuel. And diesel fuel is more suitable for small aviation application on land. In this study, numerical simulation was performed to evaluate the possibility of switching from gasoline direct injection spark ignition (DISI) to diesel DISI combustion. Diesel was injected into the cylinder by original DI system and ignited by spark. In the simulation, computational models were calibrated by test data from a DI engine. Based on the calibrated models, furthermore, the behavior of diesel DISI combustion was investigated. The results indicate that diesel DISI combustion is slower compared to gasoline, and the knock tendency of diesel in SI combustion is higher. For a diesel/air mixture with an equivalence ratio of 0.6 to 1.4, higher combustion pressure and faster burning rate occur when the equivalence ratios are 1.2 and 1.0, but the latter has a higher possibility of knock. In summary, the SI combustion of diesel fuel with a rich mixture can achieve better combustion performance in the engine.
Effects of the flow pattern of intertubular liquid film on mass and heat transfer synergies in a falling-film dehumidification system with horizontal pipes are studied. A flow model of the dehumidifying solution between horizontal pipes is established using Fluent software, the rule of transitions of the flow pattern between pipes is studied, critical Reynolds numbers of flow pattern transitions are obtained, and the accuracy of the model is verified by experiments. The mass transfer synergy angle and heat transfer synergy angle are respectively used as evaluation criteria for the mass transfer synergy and heat transfer synergy, and distribution laws of the synergy angles for droplet, droplet columnar and curtain flow patterns are obtained. Simulation results show that the mass transfer synergy angles corresponding to droplet, droplet columnar and curtain flow patterns all rise to a plateau with time. The mean mass-transfer synergy angle is 98° for the droplet flow pattern, higher than 96.5° for the droplet columnar flow pattern and 95° for the curtain flow pattern. The results show that the mass transfer synergy of the droplet flow pattern is better than that of the droplet columnar flow pattern and that of the curtain flow pattern.
Partition of unity based numerical manifold method can solve continuous and discontinuous problems in a unified framework with a two-cover system, i.e., the mathematical cover and physical cover. However, renewal of the topology of the two-cover system poses a challenge for multiple crack propagation problems and there are few references. In this study, a robust and efficient strategy is proposed to update the cover system of the numerical manifold method in simulation of multiple crack propagation problems. The proposed algorithm updates the cover system with a bottom-up process: 1) identification of fractured manifold elements according to the previous and latest crack tip position; and 2) local topological update of the manifold elements, physical patches, block boundary loops, and non-persistent joint loops according to the scenario classification of the propagating crack. The proposed crack tracking strategy and classification of the renewal cases promote a robust and efficient cover renewal algorithm for multiple crack propagation analysis. Three crack propagation examples show that the proposed algorithm performs well in updating the cover system. This cover renewal methodology can be extended for numerical manifold method with polygonal mathematical covers.
To research the characteristics of vented explosion of methane-air mixture in the pipeline, coal mine tunnel or other closed space, the experiments and numerical simulations were carried out. In this work, explosion characteristics and flame propagation characteristics of methane in pipeline and coal mine tunnel are studied by using an explosion test system, combined with FLACS software, under different vented conditions. The numerical simulation results of methane explosion are basically consistent with the physical experiment results, which indicates that the numerical simulation for methane explosion is reliable to be applied to the practice. The results show that explosion parameters (pressure, temperature and product concentration) of methane at five volume fractions have the same change trend. Nevertheless, the explosion intension of 10.0% methane is the largest and that of 9.5% methane is relatively weak, followed by 11.0% methane, 8.0% methane and 7.0% methane respectively. Under different vented conditions, the pressure and temperature of methane explosion are the highest in the pipeline without a vent, followed by the pipeline where ignition or vent position is in each end, and those are the lowest in the pipeline with ignition and vent at the same end. There is no significant effect on final product concentration of methane explosion under three vented conditions. For coal mine tunnel, it is indicated that the maximum explosion pressure at the airproof wall in return airway with the branch roadway at 50 m from goaf is significantly decreased while that in intake airway does not change overwhelmingly. In addition, when the branch roadway is longer or its section is larger, the peak pressure of airproof wall reduces slightly.
The state of clean sand was mainly dependent on its void ratio (density) and confining stress that greatly influenced the mechanical behavior (compression, dilatancy and liquefaction) of clean sand. Confirming whether the confining stress was a state variable of sand required precise element tests at different confining stress, especially the tests under very low confining stress whose test data were very limited. In this study, static-dynamic characteristics of clean sand was comprehensively investigated by a unified test program under low and normal confining stress ranging from 5 to 98 kPa, under monotonic/cyclic and drained/undrained conditions, together with the literature available data under confining stress of 1.0 to 3.0 MPa. For monotonic loading tests, the contraction/dilation phase transition was observed for loose sand at low confining stress, and dilatancy angles were stress-dependent. In addition, the liquefaction resistance was observed to increase with reducing of confining stress, and the axial strain varied from compressive to dilative when confining stress increased. Special attention was also paid to the enhancement effect of membrane, and it was observed that its influence on the test results was limited. In addition, the experimental results were proved reliable by reproducibility.
Bidirectional electromigration rehabilitation (BIEM) is a novel electrochemical rehabilitation method involving the injection of inhibitors into steel bar surface. The BIEM effect and hydrogen embrittlement (HE) risk depend on the electrochemical parameters (current density and duration) and operating condition (stress level and concrete cover thickness) of reinforced concrete structures. Experiments were performed in this study to investigate the relationships between the aforementioned factors. For a small current density group, a linear relationship was established between electric flux and chloride extraction. For a large current density group, the reasonable current density, stress level, and treatment time were obtained. Finally, the querying method of electrochemical parameters combined with treatment time and current density was proposed.
An exploratory discussion is presented on the application of egg-shaped function in elasto-plastic constitutive analysis for soft clay. Two main tasks of the paper are: 1) to propose a complete yield criterion based on egg-shaped function and supplement its definition in the deviatoric section, and then a yield criterion suitable for 3D stress conditions is obtained; 2) to elaborate its numerical implementation based on the drained triaxial tests. During the above discussion, a non-associated flow rule is proposed, in which the stress-dilatancy relationship in most classical theory is replaced by a linear dependence between the stress state parameter η and the rotation angle η of the plastic potential surface. Thereafter, isotropic and kinematic hardening behavior is considered by employing the hardening parameter H, which can be expressed as the function of plastic work Wp. Finally, comparisons between numerical results and test data on Taizhou soft clay are made to verify the effectiveness of the proposed model.
The former studies indicate that loading rates significantly affect dynamic behavior of brittle materials, for instance, the dynamic compressive and tensile strength increase with loading rates. However, there still are many unknown or partially unknown aspects. For example, whether loading rates have effect on crack dynamic propagating behavior (propagation toughness, velocity and arrest, etc). To further explore the effect of loading rates on crack dynamic responses, a large-size single-cleavage trapezoidal open (SCTO) specimen was proposed, and impacting tests using the SCTO specimen under drop plate impact were conducted. Crack propagation gauges (CPGs) were employed in measuring impact loads, crack propagation time and velocities. In order to verify the testing result, the corresponding numerical model was established using explicit dynamic software AUTODYN, and the simulation result is basically consistent with the experimental results. The ABAQUS software was used to calculate the dynamic SIFs. The universal function was calculated by fractal method. The experimental-numerical method was employed in determining initiation toughness and propagation toughness. The results indicate that crack propagating velocities, dynamic fracture toughness and energy release rates increase with loading rates; crack delayed initiation time decreases with loading rates.
The pile-supported subgrade has been widely used in high-speed railway construction in China. To investigate the ground vibrations of such composite foundation subjected to moving loads induced by high-speed trains (HSTs), three-dimensional (3D) finite element method (FEM) models involving the pile, pile cap and cushion are established. Validation of the proposed model is conducted through comparison of model predictions with the field measurements. On this basis, ground vibrations generated by HSTs under different train speeds as well as the ground vibration attenuation with the distance away from the track centerline are investigated. In addition, the effects of piles and pile elastic modulus on ground vibrations are well studied. Results show that the pile-reinforcement of the subgrade could significantly contribute to the reduction of ground vibrations. In particular, the increase of elastic modulus of pile could lead to consistent reduction of ground vibrations. However, when the pile elastic modulus is beyond 10 GPa, this benefit of pile-reinforcement on vibration isolation can hardly be increased further.
In this study, experiments were carried out to investigate aerodynamic characteristics of a high-speed train on viaducts in turbulent crosswinds using a 1:25 scaled sectional model wind-tunnel testing. Pressure measurements of two typical sections, one train-head section and one train-body section, at the windward and leeward tracks were conducted under the smooth and turbulence flows with wind attack angles between −6° and 6°, and the corresponding aerodynamic force coefficients were also calculated using the integral method. The experimental results indicate that the track position affects the mean aerodynamic characteristics of the vehicle, especially for the train-body section. The fluctuating pressure coefficients at the leeward track are more significantly affected by the bridge interference compared to those at the windward track. The effect of turbulence on the train-head section is less than that on the train-body section. Additionally, the mean aerodynamic force coefficients are almost negatively correlated to wind attack angles, which is more prominent for vehicles at the leeward track. Moreover, the lateral force plays a critical role in determining the corresponding overturning moment, especially on the train-body section.