In this investigation, the high-velocity oxygen fuel (HVOF) deposition technique was implemented to administer vanadium carbide (VC) and cupronickel-chromium (CuNiCr) composite coatings onto SS316 stainless steel. The significance of this research lies in its direct relevance to addressing corrosion-related challenges in marine environments. Preceding and subsequent to the execution of electrochemical corrosion examinations within a 3.5% sodium chloride (NaCl) medium at ambient temperature, a comprehensive scrutiny of the surface topographies of both the coated and uncoated specimens was conducted through scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The outcomes manifest that the intermetallic binder composed of copper (Cu), nickel (Ni), and chromium (Cr) within the coatings undergoes deterioration under the influence of the NaCl medium, thereby inducing localized pitting corrosion phenomena across the substrate. Intriguingly, the incorporation of VC within the coating formulation conspicuously amplifies the corrosion resistance attributes of the treated surface, thereby ameliorating the occurrence of confined corrosive pits. Amidst the assortment of coatings subjected to scrutiny, the VC imbued surface attains the most favorable outcome, showcasing minimal corrosion rate of 72.38×10−3 mm/a. In contrast, the SS316 base substrate exhibits the most escalated corrosion rate calculated at 783.82×10−3 mm/a.
In order to solve the formation of brittle compounds in brazed joints, an innovative rare earth modified reduced graphene oxide reinforced AgCuTi composite brazing filler was designed to achieve brazed joints with Ag-Cu eutectic as the main organization almost free of brittle compounds, and at the same time, the dispersion of graphene in the joint interfaces was improved. Microanalysis and discussion of the brazing fillers with and without Ce modification showed that the Ce modified reduced graphene oxide was more uniformly dispersed in the brazing fillers. The interfacial microstructures of C/C composites-C/C composites joints with and without Ce modified brazing fillers were compared, and the effect of graphene content on the organization and properties of the joints was investigated. The results showed that the shear strength of the joints was significantly enhanced by using Ce modified brazing fillers. When the graphene content was 0.5 wt.%, the average shear strength of the brazed joints obtained by using Ce modified brazing fillers was 31.82 MPa, increased by 50%.
With the rapid development of the aerospace industry, there is an increasing demand for miniaturized parts made of Inconel 718 foils. However, the grain size effect on the plastic deformation behavior of thin sheets is significant, which considerably limits the fabrication and application of micro-components from Inconel 718. In this study, a series of uniaxial tensile tests and scanning electron microscopy experiments were conducted on Inconel 718 foils with different grain sizes to investigate the grain size effect on plastic deformation behavior. The grain size, orientation, and kernel average misorientation were characterized via electron backscatter diffraction to elucidate the deformation mechanism associated with the grain size effect. The results demonstrate that as the grain size increased, the number of grain orientations transforming into gradually decreased owing to weakened grain rotation and coordination under tensile stress, leading to a significant reduction in yield strength and maximum tensile strength. Additionally, the plastic deformation within the grain interior diminished significantly, while grain boundary sliding became a prominent deformation mechanism during tension as grain size increased, resulting in decreased fracture strain and ductile fracture characteristics. Finally, a mixed material constitutive model incorporating grain size and strain was developed for microforming research on Inconel 718 foils.
Due to the increased service temperature of turbine blades, the high temperature conditions seriously deteriorate the mechanical properties of nickel-based superalloys, thus it is necessary to prepare the anti-oxidation coating. This research investigated the microstructure evolutions and oxidation behaviors of simple and silicon-modified aluminide coatings at 1000 °C for 200 h. After oxidation, serious spalling out and failure appeared due to spinal NiCr2O4 and volatile Cr3O phase formation in the IN718 superalloy. For the aluminide coating, the formation of stable α-Al2O3 oxide film significantly improved the oxidation resistance, with a mass gain of only 0.1 mg/cm2 during the oxidation of 100–200 h. The silicon-modified aluminide coating exhibited the lowest mass gain, rapidly formed stable SiO2 oxide film due to the existence of the Cr9.1Si0.9 phase and maximum grain size in the external coating, and the internal Al2O3 oxide together with the coating formed the pinning effect, effectively preventing the delamination of the oxide film. However, the formation and growth of the Ni3Si phase generated microcracks, leading to its rate of mass gain surpassing that of aluminide coating during oxidation of 100–200 h, which illustrates that effectively regulating the Si content is imperative to prolonging the service life of turbine blades.
Manganese dioxide (MnO2) is considered one of the most promising cathode materials for aqueous zinc-ion batteries because of its high theoretical capacity, high working voltage, and environmental friendliness. However, its severe capacity fading is caused by unstable crystal structure and manganese dissolution during discharge. Based on these reasons, dicyandiamide (DCDA) was used to coat α-MnO2 and the effect mechanism of DCDA on the electrochemical performance of α-MnO2@DCDA was systematically investigated. The results indicate that the physical confinement function of the DCDA not only improves significantly the structural stability of α-MnO2 but also inhibits dissolution of manganese during discharge. More importantly, electrostatic interaction between nitrogen atoms in DCDA and cations in electrolyte can inhibit Mn2+ dissolution during discharge and promote Mn2+ deposition during charging, effectively inhibiting the loss of manganese active material. Compared with unmodified α-MnO2 cathodes, α-MnO2@DCDA cathodes exhibit significantly improved cycling stability, with a stable capacity of 102.6 mA·h/g after 1500 cycles at a high current density of 3 A/g, with a capacity retention rate exceeding 60%. This work provides an effective way to achieve stable cycling of MnO2-based zinc-ion batteries.
The non-ammonia thiosulfate leaching system is considered to be an attractive and eco-friendly route for gold leaching without the usage of cyanide or ammonia. In this paper, the role of four organic carboxylic acids, named oxalic acid (Ox), malic acid (Mal), citric acid (Cit), and tartaric acid (Tart) in copper-thiosulfate system has been studied comparatively. Based on the available thermodynamic data, a series of E h–pH and species distribution diagrams for copper-Ox/Mal/Cit/Tart-thiosulfate system under various conditions have been constructed from thermodynamic calculation. The results show that thiosulfate is the only effective complexing agent for aurous ions, while the organic carboxylic acids work as a copper ligand. The copper-Mal/Cit/Tart-thiosulfate system exhibits potential advantages over the traditional copper-ammonia-thiosulfate system, such as wider pH range and lower thiosulfate consumption. The calculation also indicates the redox potentials of Cu(II)/Cu(I) for the leaching systems are in the subsequence of E 0[Cu(Ox)2 2−/Cu(S2O3)3 5−] >E 0[Cu(NH3)4 2+/Cu(S2O3)3 5−] >E 0[Cu2(Mal)2H−2 2−/Cu(S2O3)3 5−] ≈E 0[Cu2(Cit)2H−2 4−/Cu(S2O3)3 5−] > E 0[Cu(Tart)2H−4 6−/Cu(S2O3)3 5−]. Increasing thiosulfate concentration leads to a sharp decline in the content of copper-Ox/Mal/Cit/Tart complex, and the stability of the formed cupric complex follows the descending order of tartaric acid>citric acid>malic acid>oxalic acid.
The dissolution behaviors of Cu and Fe from copper slags were investigated with photochemical reactions. Experiments were run intermittently with a quartz glass jacket in a glass reactor, by submerging ultraviolet (UV) lamps and using glass tube as an air supply distributed under the reactor. The behaviors of UVA (365 nm), UVB (311 nm), UVC (254 nm), and vacuum-UV (VUV) (185 nm) light at different wavelengths in a leaching solution were examined. All experiments were conducted comparatively in the presence and absence of UV lamps under identical conditions. The adaptation of the radical formation mechanism to the leaching environment and its usability in leaching by creating an oxidative solution medium were investigated. In the experiments in the UV light (185 nm) and non-UV light environments under optimum conditions, the copper extraction rates were obtained as 85.1% and 70.7%, respectively. In conclusion, the metal dissolution (Cu) behaviors at optimum conditions during leaching from copper slags in the photoreactor systems with UV (185 nm) light were more efficient than those without UV light. Moreover, photochemical reactor is a new approach to adapt them to hydrometallurgy applications and examine the process.
In this paper, sinter samples of limonitic nickel laterite were adopted for Fe-Cr-Ni alloy preparation at lower costs. Based on the thermodynamics analysis, smelting characteristics of sinter samples of S1 (4.84 wt% Cr2O3) and S3 (7.72 wt% Cr2O3) were revealed by the optimization of smelting process parameters. When smelting durations were kept at 60 min and 90 min for S1 and S3 and smelting temperature, coke dosage and slag basicity were maintained at 1600 °C, 20 wt% and 1.0, respectively, the qualified Fe-Cr-Ni alloys containing 84%–88 wt% Fe, 5.6%–9.3 wt% Cr and 1.55%–1.70 wt% Ni were prepared with the recovery rates of Fe, Cr and Ni of over 96%, 90% and 98%, respectively. Higher Cr2O3 content of sinter leads to the prolongation of smelting duration, which is adverse to the reduction of coke ratio and the increase of stainless steel output. The comprehensive furnace burdens including Ni-bearing sinter and Cr-bearing pellets will be developed in the follow-up study for the more efficient preparation of high-Cr ferronickel.
In view of the two major problems of the rapid growth of global CO2 emissions and the high cost of mine backfill materials (cement). In this study, a new method of mixing coal gangue (CG), magnesium slag (MS) and fly ash (FA) and preparing a backfill material without cementitious material through carbonation curing was proposed, and two kinds of magnesium slag based full-solid waste backfill materials (CM and CMF) with high strength, low cost and carbon fixation were prepared. Uniaxial compressive strength (UCS), X-ray diffraction (XRD), thermogravimetric differential thermal analysis (TG-DTG), mercury injection (MIP) and other test methods were used to investigate the effects of different curing ages, MS and FA contents on the carbonation properties of CM and CMF. The results showed that carbonation curing significantly improved the early strength of CM and CMF, and the fracture surface became colorless under phenolphthalein indicator at 7 d, reaching the degree of complete carbonation. After 7 d of carbonation curing, the compressive strength of CM and CMF reached 7.048 MPa and 8.939 MPa, which increased 25.2 times and 29.4 times compared with the standard curing, and the compressive strength of CM increased with the increase of MS content, and the compressive strength of CMF first increased and then decreased with the increase of FA content. The backfill effect of carbonized products makes the microstructure of CM and CMF denser, improves the pore size distribution, reduces the cumulative pore volume and total porosity, and promotes the improvement of strength properties. In addition, CM and CMF can absorb up to 16.34% of CO2 through this carbonation curing method. Therefore, this study confirms that the method can not only prepare a CM and CMF without using gelling materials, but also provide a new path for the combination of solid waste disposal, low-cost backfill and CO2 storage.
High-voltage electric pulse (HVEP) technology merits further investigation into its potential applications. The effectiveness of using HVEP to induce pre-damage and deteriorate hot dry rock (HDR) was investigated in this study. Different peak voltages of HVEP were applied to heated-granite flake specimens. Furthermore, the influence of temperature on HVEP stimulating granite was investigated. The results show that when the applied peak voltages exceeded 96 kV, through-fracture failure occurred in the heated-granite specimens, with higher voltages producing more complex through-fracture networks. The microcrack density of granite specimens increased from 8.63 mm/mm2 to 13.26 mm/mm2 when the applied voltage rose from 96 kV to 144 kV. Notably, the difficulty of granite electrical breakdown gradually decreased with the increasing temperature of thermal treatment. Through-fracture failures were observed in all granite specimens heated above 400 °C after three HVEP discharges at 120 kV. The maximum damage caused by HVEP was found within the temperature range of 300–400 °C. Additionally, an escalation in the development of internal pores and cracks as the granite specimen temperature increased was observed by using scanning electron microscopy (SEM), accompanied by an increase in pore size and crack width and depth.
This paper utilizes physical and numerical model experiments to study the deformation and failure mechanisms of goaf-side entries driving adjacent to longwall top coal caving (GEDLTCC) panel. The physical model experiment reveals that the deformation and failure process of GEDLTCC can be divided into four stages: initial deformation stage I (− 47 m to 45 m behind the adjacent panel), rapid deformation stage II (45 to 150 m), deformation stabilization stage III (150 to 240 m) and compaction stabilization stage IV (beyond 240 m). Notably, large deformation of the GEDLTCC surrounding rock primarily occurs during stages II and III. This deformation is primarily attributed to the stress concentration resulting from the lateral cantilever beam structure above the goaf-side entry. Therefore, this paper proposed an innovative approach that employs roof pre-splitting technology to optimize the roof structure, thereby controlling the large deformation of GEDLTCC and automatically retaining entry. Numerical simulations and field applications show that after adopting the automatically retained entry by roof pre-splitting (ARERP) technology, the abutment pressure of the integrated coal and the convergence of roof-to-floor and two ribs were reduced by 6.49%, 79.25% and 60%, respectively. Therefore, ARERP technology can effectively control the deformation of the GEDLTCC.
Cemented gangue backfill technology is an important backfill mining method. However, the acid mine water environment could seriously affect the strength of the cemented gangue backfill body (CGBB). In this study, CGBB specimens were placed in different environments (air, water, H2SO4 solution, and H2SO4 solution coupled with load) to test the strength, resistivity, and ultrasonic pulse velocity (UPV) of CGBB at different ages. The acoustic emission (AE) energy of the specimens during loading was monitored, and the microstructure was analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Test results showed that: 1) The strength of CGBB cured in air and water gradually slowed down with age. The strength of CGBB in the H2SO4 solution was greater than that of CGBB cured in air or water in the first 90 d. The strength of CGBB under the coupling of the H2SO4 solution and load decreased more slowly with age than that of the single H2SO4 solution; 2) The resistivity and UPV had a good corresponding relationship with the strength of the CGBB. The failure modes of the CGBB after erosion were various, and the CGBB showed different AE energy characteristics at different stages of loading. The surge of AE energy could be used as a precursor to the failure of CGBB; 3) Erosion products compacted CGBB in the early stages and improved its strength. In the later stage, the CGBB cracked under the action of expansion stress and the strength decreased. Applying a 40% stress-to-strength ratio would resist the erosion of the H2SO4 solution. The research could provide a reference for the design of the corrosion resistance of CGBB.
In paste backfill mining, cemented coal gangue-flyash backfills (CGFB) can effectively control surface subsidence. CGFBs are subjected to water pressure and chloride ion erosion in the gob. Therefore, an improved understanding of the influence of pressurized water and chloride salt erosion on the performance of CGFB is crucial for realizing effective green mining. In this study, CGFB samples were soaked in a NaCl solution at 0, 0.5, 1.5, or 3.0 MPa for 15 d. The mechanical properties of the samples and deterioration mechanisms were investigated using uniaxial compression tests, acoustic emission tests, digital speckle strain measurements, scanning electron microscopy, and X-ray diffraction. The results show that the uniaxial compressive strength (UCS) increased and then decreased with the increase of soaking pressure. When the soaking pressure increased from 0 to 1.5 MPa, the average UCS increased by 43.5%. Then, when the soaking pressure increased from 1.5 to 3.0 MPa, the average UCS decreased by 18.9%. Moreover, water pressure promotes chloride ions into the interior of CGFB and the production of Friedel’s salt. Higher water pressures-chloride salt erosion coupling increases the porosity of CGFB, with the 3.0 MPa sample showing an 8.2% increase in porosity compared to the 0 MPa sample. Thus, internal pore cracks developed and penetrated the samples, which degraded their mechanical properties and reduced their strength and compactness.
Seawater coral aggregate concrete (SCAC) has demonstrated advantages in reducing material cost and energy consumption of marine infrastructure on reefs and islands. However, SCAC exhibits increased brittleness and higher dependency on coral aggregate type as its strength increases. In this study, two types of coral aggregates are used to compare their influence on SCAC performance. Flexible fiber and rigid fiber are blended to improve the strength, toughness, and fracture properties of SCAC. The results show that the compressive strength of SCAC incorporating low-strength coral aggregate is reduced by 30.8% when comparing to that containing high-strength coral aggregate (from 55.6 to 38.5 MPa). Fiber incorporation could mitigate the strength reduction that originated from weaker coral aggregates. A novel constitutive model is proposed to describe the stress-deformation curves of SCAC. Good agreement between the model prediction and test data is observed. Relative to reference group, the fracture energies of SCAC adding 0.1%, 0.2%, and 0.3% polyvinyl alcohol fibers are increased by 10%, 49%, and 88% respectively. The fracture energies of hybrid fiber groups are 46% higher than that of mono fiber groups with the same fiber dosage.
Rice husk ash (RHA) is currently utilized as a supplementary cementitious material in cement products due to its pozzolanic properties. This study aims to investigate the pozzolanic effect (PE) and filler effect (FE) of RHA on the mechanical properties and microstructure of cemented paste backfill (CPB). The effects of RHA content, cement-to-tailings ratio, and mass concentration on the unconfined compressive strength (UCS) of the CPB were investigated. The proportion of UCS that could be attributed to the PE was 67.30%–87.92% higher than the FE in CPB with RHA contents ranging from 10% to 20%. The FE of RHA exerted stronger influence at lower curing times, but the PE played more crucial roles at curing times of more than 3 d. These results provide new insights into the potential use of RHA as a cementitious material for use in backfilling during mining operations.
The three-dimensional (3D) fractal contact model of the interaction between gear teeth is established considering the actual surface morphology of gear teeth. The time-varying meshing stiffness (TVMS) model of spur gear pair is established and verified by finite element (FE) method based on the loaded tooth contact analysis (LTCA) method and considering the influence of friction between the gear teeth. The meshing characteristics and wear depth under tooth surface wear fault condition are analyzed by incorporating the Archard’s wear model, considering the effects of tooth roughness and friction. The effects of friction and fractal parameters on TVMS and wear depth are analyzed. Friction causes the TVMS at the pitch line position to mutate. The increase in friction coefficient and decrease in fractal dimension result in the increase in wear depth and the decrease in TVMS within the region where two pairs of gear teeth engage in meshing. TVMS shows partial linearity with the change of fractal dimension. The influence of fractal dimension on TVMS and wear depth becomes increasingly prominent with the progression of wear cycles, surpassing the influence of friction coefficient.
Inferior vena cava filter (IVCF) could reduce the risk of fatal pulmonary embolism. However, procedural difficulties often exist during IVCF retrieval, requiring extra devices and venous access. Thus, an effective prediction model is essential to predicting the difficulties in preoperative planning, hence aiding efficient intraoperative cooperation. This study retrospectively analyzed 477 cases of IVCF retrievals in the center of the Third Xiangya Hospital of Central South University from 2011 to 2020, among which 344 cases were defined non-difficult retrieval and 133 cases as difficult retrieval (including 35 failed retrievals). The cases before 2017 were classified as training cohort (TC), while the rest as validation cohort (VC). A nomogram was generated to predict IVCF retrieval difficulty with risk factors validated by univariate and multivariate logistic regression analysis. The study then evaluated the model performance with calibration plot, receiver operating characteristic curve (ROC) and decision curve analysis (DCA). It is shown that IVCF retrieval difficulty increases significantly when factors of embedded top of the filter, leg penetration, and irregular anticoagulation occur. Moreover, the nomogram shows the predictive accuracy values of TC and VC are 0.819 and 0.817, respectively. The calibration curve of TC and VC indicates that the model can effectively predict the risk of difficult retrieval. This nomogram has good predictive effect and low generalization error, which can provide evidence for surgical decision of IVCF retrieval.
Shale oil is an important area for the increasing of crude oil reserves and production. Due to the tight structure and ultra-low permeability of shale oil reservoir, the industrial exploitation needs large-scale hydraulic fracturing. However, compared with marine shale reservoirs, the Chang 73 lacustrine shales of the Ordos Basin present large differences in mineral composition and rock fabric, resulting in strong mechanical heterogeneity. The target interval selection and effective hydraulic fracturing of lacustrine shale oil reservoir requires a thorough understanding of the mechanical behavior and hydraulic fracture propagation in shale rocks. In-situ X-ray CT mechanical tests and triaxial hydraulic fracturing tests on Chang 73 lacustrine shales were conducted. The effects of rock fabric, in-situ stress difference and fluid viscosity on hydraulic fracture vertical propagation were analyzed. The results show that the rock fabric significantly influences the mechanical behavior and failure process of lacustrine shales. The vertical growth of the hydraulic fracture in lacustrine shales is dictated by vertical stress difference and fluid viscosity. When the vertical stress difference is small, the intrinsic weak interfaces in black shale significantly inhibit the vertical growth of hydraulic fracture. With the increase of vertical stress difference, the fracture network volume of black shale increases linearly, however, the fracture volume of laminar shale first increases and then decreases. Increasing the fracturing fluid viscosity could weaken the obstruction effect of weak bedding interfaces and promote the vertical propagation of hydraulic fracture.
Gravity anomalies generated by density non-uniformity are governed by the 3D Poisson equation. Most existing forward methods for such anomalies rely on integral techniques and cell-centered numerical approaches. Once the gravitational potential is calculated, these numerical schemes will inevitably lose high accuracy. To alleviate this problem, an accurate and efficient high-order vertex-centered finite-element scheme for simulating 3D gravity anomalies is presented. Firstly, the forward algorithm is formulated through the vertex-centered finite element with hexahedral meshes. The biconjugate gradient stabilized algorithm can solve the linear equation system combined with an incomplete LU factorization (ILU-BICSSTAB). Secondly, a high-degree Lagrange interpolating scheme is applied to achieve the first-derivate and second-derivate gravitational potential. Finally, a 3D cubic density model is used to test the accuracy of the vertex-centered finite-element algorithm, and thin vertical rectangular prisms and real example for flexibility. All numerical results indicate that our high-order vertex-centered finite-element method can provide an accurate approximation for the gravity field vector and the gravity gradient tensor. Meanwhile, compared to the cell-centered numerical algorithm, the high-order vertex-centered finite element scheme exhibits higher efficiency and accuracy in simulating 3D gravity anomalies.
Delayed rockburst experiments with different numbers of unloading surfaces (DNUS) were performed using an independently developed true triaxial multisurface unloading rockburst experimental system. Based on the rockburst excess energy theory, the energy storage characteristics, excess energy, excess energy release rate (EERR), and crack evolution characteristics of rockbursts with DNUS were studied, and the following main conclusions were obtained. The occurrence of rockbursts is mainly due to the generation of an excess energy ΔE. ΔE depends on the elastic strain energy stored in the rock before the rockburst, the energy input by the equipment after the peak, and the residual elastic strain energy. As the DNUS increases, ΔE gradually decreases, but the EERR value increases, and the rockburst becomes increasingly severe; Rapid unloading of the specimen under true triaxial high-pressure loading will produce an unloading platform in the stress–strain curve, causing unloading damage. The damage is mainly concentrated near the free surface in the form of tension failure, and the unloading damage gradually increases with increasing DNUS; Tensile cracks play a dominant role in the damage and destruction of sandstone. In the final rockburst stage, the slope of the shear crack curve was greater than that of the tensile cracks, indicating that shear cracks were a critical factor affecting the instability and failure of the specimen.
Tensile-shear failure commonly occurs during the construction of deep in-situ tunnels. In this paper, direct tensile-shear tests were conducted on rock-like specimens containing regular serrated joints using a self-developed multifunctional rock mechanical test system. The influence of joint undulation angle variation on the tensile-shear strength, temperature, and acoustic emission (AE) was investigated. The results showed that the peak shear strength of the specimen decreased with the increase of joint undulation angle, and the increase of joint undulation angle led to the rock bridge being more prone to tensile failure and made the crack contour exhibit an obvious step-like feature. When approaching failure, the specimens all generated vigorous AE signals and yielded more cracks, which were accompanied by energy dissipation and manifested a decrease in temperature. During the loading process of the three specimens, the AE b values exhibited an overall trend of first increasing and then decreasing, with a dramatic fall near the peak strength. Cracks were classified by RA-AF values, and the results showed that in the initial loading process, the cracks were primarily of pure tensile types. The number of shear and composite cracks increased significantly when the specimens were close to failure.
With the increasing speed of high-speed trains, the periodic short-wave irregularities caused by high-frequency vibration between wheel and rail inevitably cause potential severe damages to vehicle and track components. To gain an insight into the attenuation pattern of high-frequency vibration in the bottom-up transmission, it is necessary to investigate in-depth the vibration characteristics of the coupled vehicle system under high-frequency excitation. First, the spectrum of track irregularities with a wide frequency range is obtained via regression analysis of collected real measured data. Inversion analysis is followed conducted to obtain samples of irregularities within wavelength range of 0.002–100 m. Next, a rigid-flexible wheel-rail coupling dynamics model is built with the wheelset and the rail adopting elastic bodies. High-frequency vibration characteristics of the wheel and rail caused by periodic short-wave irregularities are then simulated and analyzed. The results show that the vibration of the vehicle components distributes in the frequency range of 30–1390 Hz, and the vibration attenuates from the bottom layer to the top layer. Finally, the quantitative limit value for the typical wavelength of periodic short-wave irregularities under the train speed of 400 km/h is further precisely calculated by extracting the influence of the amplitude variations of periodic short-wave irregularities on the wheel-rail interaction.
Floating slab track is widely used in urban rail transit because of its proven vibration attenuation and isolation performance. To investigate the elastic wave propagation in floating slab structure, the characteristic equation for wave dispersion is obtained using generalized plane wave expansion. Double periodicities from unit slab and fastener spacing are considered simultaneously. The complex dispersion curve of the infinite periodic floating slab track is obtained. Eight band-gaps are found to exist in the range from 0 to 300 Hz, and the corresponding theoretical analysis on wave dispersion is provided. An impact test was conducted, which verifies the band-gaps blocking effect on elastic wave propagation. Based on the wave-mode properties, it is found that the band-gap formation mechanism of track structure with double periodicities is different from track structure with a single periodicity, i.e., the localized Bragg scattering or localized resonance modes cannot prevent the propagation of coupled elastic waves in the case of double periodicities. The results in the frequency-wave number domain demonstrate that anomalous Doppler effect occurs in the stopband range and the normal Doppler effect occurs in the passband range.