Bed Layer Research Articles

The diffusion process of the dense medium and its effects on the beneficiation of 0–6 mm oil shale in the continuous vibrating air dense medium fluidized bed

As an important alternative energy resource, oil shales have a large number of potential applications. In ore, many inorganic mineral impurities can be produced simultaneously during the mining process. Through the physical separation methodology, the impurities can be effectively removed and the concentrate can be enriched. This study analyzed the diffusion process of heavy-medium oil shales and its impact on the separation of the oil shale in a continuous vibrating air dense medium fluidized bed (CVADMFB). The migration characteristics of the dense medium along the transverse (X-axis) and longitudinal (Z-axis) direction were systematically analyzed. The effects of the operating parameters (vibration amplitude and frequency, gas velocity) on the stability of the bed density were studied, and the optimum parameters were determined. Then, the oil shale was separated under the optimal factors. The results showed that in the transverse (positive X-axis) direction, the trajectories of particles migrating from the sidewall to the center of the bed were formed at the feeding end and then gradually spread to the discharge end. Finally, the transversal diffusion process was completed. However, due to the limitations of the particle migration area in the longitudinal diffusion process, the backmixing problem arises during the migration process of the dense medium and it gradually disappears as the beneficiation evolves. Finally, the uniform mixing is completed. In the process of oil shale separation under the optimal process parameters, the rapid-loose zone, the segregation layer zone, and the separation checking zone are formed successively along the longitudinal direction of the bed layer. When the vibration amplitude (A), frequency (f), and the operating gas velocity (Uv) were 2.5 mm, 26 Hz, and 0.152 m/s, respectively, the oil content and the yield of the concentrate were 10.12% and 33.2%. The oil content and the yield of the tailings were 0.71% and 66.8%, respectively. The probable error E was 0.11 g/cm3. The results show that the oil shale can be effectively purified and upgraded by CVADMFB.

Geoelectric investigation of the suitability of a proposed foldot ventures potable water factory site, Ipinsa, near Akure, southwestern Nigeria

This study is aim at determining the suitability of sitting a potable water factory within Chief Akin Omosebi layout off Ipinsa-Ilara road, near Akure, Ondo State, Nigeria by evaluating the groundwater potential, the aquifer overlying layer protective capacity and the foundation beds competence of the area. A total of twenty (20) vertical electrical soundings (VES) data were acquired along five (5) traverses using Schlumberger array with maximum half-current electrode separation of 150 m. Three curve types were delineated in the area (K, KH and KQ). The VES results delineated three to four geoelectric layers across the study area. The resistivity of the top soil, lateritic weathered layer, clayey sand weathered layer and weathered bedrock/fresh bedrock varies from 187 - 1212, 682 - 4164, 219 - 1157 and 77 - 3525 ohm-m respectively. This study reveals that the area is characterized by high groundwater potential and competent subsurface layers that can serve as foundation bed, but the aquifer layer must be well protected from pollution since the overlying layer(s) longitudinal conductance is less than 1.0 mhos which indicates that the underlying aquifer unit(s) are vulnerable to surface pollution. Keywords : Groundwater potential, aquifer overlying layer, protective capacity, longitudinal conductance and foundation beds competence.

Interlayer adhesion and fracture resistance of polymers printed through melt extrusion additive manufacturing process

This study aims to establish the relationships between the process parameters, mesostructural features (interlayer neck and void sizes), and the fracture resistance of 3D printed parts. The proposed method enables the decoupling of bond quality and mesostructure effects on the overall fracture behavior. Double cantilever beam specimens of acrylonitrile butadiene styrene (ABS) were designed, printed, and fracture tested. The apparent fracture resistance (Jc,a), the interlayer fracture resistance (Jc,i), and the microstructure were characterized. The fracture results and the microscopic examinations indicate that Jc,a is strongly correlated with the process parameters through both the interlayer adhesion as well as the mesostructure. Nozzle and bed temperatures and layer height were found to have significant effects on the fracture behavior. For instance, the Jc,a increased by 38% with a 20 °C increase in the nozzle temperature. This originated from 15% increase in the interlayer fracture resistance and 23% increase in the actual fracture surface area (interlayer neck size). The quality of interlayer bond was explained in terms of temperature, pressure, and time of the process. This work quantifies the relationships between the printing process and the fracture behavior and provides novel tools and insights in the design and analysis of printed materials.

Benthic foraminiferal turnover across the Paleocene–Eocene Thermal Maximum (PETM) event in Eastern Desert, Egypt

Benthic foraminiferal fauna are analyzed quantitatively and qualitatively at three stratigraphic sections in Eastern Desert of Egypt (Serai, Duwi, and Um El Huetat). These sections embrace the Paleocene–Eocene Thermal Maximum (PETM) interval which is represented by the occurrence of five distinctive beds. These beds constitute the Dababiya Quarry Member at the lower part of Esna Formation. The occurrence of them indicates an expanded and relatively continuous record across the P/E boundary. The organic-rich clay layer (bed no. 1 of the Dababiya Quarry Member) marks the start of the PETM event. This bed is characterized by the extinction of all benthic foraminiferal fauna except for the occurrence of rare agglutinated foraminiferal species. The presence of these species indicates an oceanic anoxic event at the sea floor. High concentration of phosphatic contents including fish remains occurred in the middle part of the PETM (bed nos. 2 and 3 of the Dababiya Quarry Member) with the continuous absence of benthic foraminiferal fauna except for few specimens at the top of bed 3. Bed nos. 4 and 5 of the Dababiya Quarry Member represent the upper part of the PETM and the initial stage of sea floor recovery. Low diversity and abundance of benthic foraminiferal taxa occurred within these beds, represented by Valvulineria scrobiculata, Lenticulina midwayensis, Loxostomoides appliane, and Siphogenerinoides eleganta. This phenomenon continues upward during the post-PETM event. The Paleocene velasco-type benthic foraminifera Angulogavelinella avnimelechi and Coryphostoma midwayensis species are extinct within the advent of the PETM event. The benthic foraminiferal assemblages at the studied sections are dominated by midway-type fauna with little representative of velasco-type fauna. The velasco-type species are represented with high abundance at Serai section and with low densities at Um El Huetat section, while at Duwi section, they rarely occurred. This suggests outer neritic-upper bathyal (150–400 m) setting at Serai section and mostly middle-outer neritic (50–150 m) setting at Um El Huetat and Duwi sections.

Investigation of a novel combination of adsorbents for hydrogen purification using Cu-BTC and conventional adsorbents in pressure swing adsorption

This study is an attempt to simulate and analyze a lab-scale two-bed pressure swing adsorption in order to investigate the performance of three different adsorbents (Cu-BTC as a new generation adsorbent, activated carbon, and zeolite 5A) with different feed compositions, and find a novel combination of layered bed. Four different flows of steam methane reforming reactor were considered as inlet feeds for hydrogen purification. Comparison of the feeds with different compositions showed that in the presence of high amounts of impurities, an adsorption bed of Cu-BTC produces hydrogen at a higher purity than activated carbon, zeolite 5A, or an activated carbon-zeolite 5A layered bed. The simulation results from feed 4 (H2:CO2:CO:CH4 = 0.4574:0.3174:0.0622:0.1630) with high amounts of impurities, showed that the use of Cu-BTC leads to hydrogen purity of up to 97.22%, while activated carbon, zeolite 5A, and the layered bed cannot improve the purity beyond 86.46%. This work shows that Cu-BTC is capable of being used in the first layer of layered beds. This was confirmed by comparing the performance of the three combinations of Cu-BTC, activated carbon, and zeolite 5A. The first configuration of the three adsorbents, in which the Cu-BTC was used as the first layer, purified hydrogen up to + 99.99% and recovered it up to 21.25%.

Anacoracid sharks and calcareous nannofossil stratigraphy of the mid-Cretaceous ‘upper’ Gearle Siltstone and Haycock Marl in the lower Murchison River area, Western Australia

Siversson, M., Cook, T.D., Ryan, H.E., Watkins, D.K., Tatarnic, N.J., Downes, P.J. & Newbrey, M.G. 5 June 2018. Anacoracid sharks and calcareous nannofossil stratigraphy of the mid-Cretaceous Gearle Siltstone and Haycock Marl in the lower Murchison River area, Western Australia. Alcheringa 43, 85–113.Extensive bulk sampling over the past 20 years and greatly improved stratigraphic control permitted a meaningful revision of previously described anacoracid sharks from the ‘upper’ Gearle Siltstone and lower Haycock Marl in the lower Murchison River area, Western Australia. Isolated teeth of anacoracids are rare in the lower three (Beds 1–3) of four stratigraphic units of the ‘upper’ Gearle Siltstone but relatively common in the uppermost layer (Bed 4) and in the lower part of the overlying Haycock Marl. On the basis of calcareous nannofossils, Beds 1 and 2 of the ‘upper’ Gearle Siltstone can be placed in the uppermost upper Albian calcareous nannofossil Subzone CC9b whereas Bed 3 can be referred to the lowermost Cenomanian CC9c Subzone. Bed 1 yielded fragments of strongly serrated anacoracid teeth as well as a single, smooth-edged tooth. The samples from Beds 2 and 3 contained a few small fragments of serrated anacoracid teeth. Bed 4 is barren of calcareous nannofossils but the presence of a dentally advanced tooth of the cosmopolitan lamniform genus Cretoxyrhina in combination with the age of the overlying Haycock Marl indicate deposition within the younger half of the Cenomanian. The unit produced teeth of two anacoracids; Squalicorax acutus sp. nov. and S. bazzii sp. nov. The basal, laminated part of the Haycock Marl is placed in the uppermost upper Cenomanian part of CC10b. It yielded Squalicorax mutabilis sp. nov. and S. aff. S. bernardezi. Exceptionally well-preserved teeth of the former species span a 5:1 size ratio range for teeth of comparable jaw position. The teeth reveal strong ontogenetic heterodonty with a large increase in the relative size of the main cusp with age and the transition from a vertical distal heel of the crown in very young juveniles to a sub-horizontal, well demarcated heel in ‘adult’ teeth. An isolated phosphatic lens in the lower part of the Haycock Marl produced calcareous nannofossils indicative of the CC10b SubZone, most likely the lowermost lower Turonian part. It contains teeth of Squalicorax mutabilis sp. nov., S. aff. S. bernardezi, and S. sp. C.Mikael Siversson* [mikael.siversson@museum.wa.gov.au], Helen E. Ryan [helen.ryan@museum.wa.gov.au] and Peter Downes [peter.downes@museum.wa.gov.au] Department of Earth and Planetary Sciences, Western Australian Museum, 49 Kew Street, Welshpool, Western Australia 6106, Australia; David K. Watkins [dwatkins@unl.edu] Department of Earth and Atmospheric Sciences, University of Nebraska, Lincoln, NE 68588, USA; Todd D. Cook [tdc15@psu.edu] School of Science, Penn State Behrend, 4205 College Drive, Erie, PA 16563, USA; Nikolai J. Tatarnic† [nikolai.tatarnic@museum.wa.gov.au] Department of Terrestrial Zoology, Western Australian Museum, 49 Kew Street, Welshpool, Western Australia 6106, Australia; Michael G. Newbrey‡ [newbrey_michael@columbusstate.edu] Department of Biology, Columbus State University, Columbus, GA 31907-5645, USA. *Also affiliated with: School of Molecular and Life Sciences, Curtin University, Kent Street, Bentley, WA 6102, Australia. †Also affiliated with: Centre for Evolutionary Biology, University of Western Australia, Crawley, Western Australia 6009. ‡Also affiliated with: Canadian Fossil Discovery Centre, 111-B Gilmour Street, Morden, Manitoba R6 M 1N9, Canada.http://zoobank.org/urn:lsid:zoobank.org:pub:97D5131F-C0D5-4A7E-9C9A-0FDF13BFCBBBhttp://zoobank.org/urn:lsid:zoobank.org:act:5977DCC2-355C-4732-8B0A-4BD0EABBA8DEhttp://zoobank.org/urn:lsid:zoobank.org:act:2D7C4147-B756-4434-847A-B0C1C6D167DFhttp://zoobank.org/urn:lsid:zoobank.org:act:33F3B55E-41E0-45B3-8296-A3B95C17B41D

Characteristics of tar abatement by thermal cracking and char catalytic reforming in a fluidized bed two-stage reactor

With respect to the newly proposed fluidized bed two-stage (FBTS) gasification process, the researches on tar thermal cracking and catalytic removal by char bed layer were conducted on a FB two-stage reaction apparatus. It shows that the effect of char on tar removal was much related to the reaction temperature and residence time of tar-containing fuel gas in the tar reformer. Under the tested experimental conditions, increasing reaction temperature and residence time can effectively promote tar abatement and generate more H2, CO and CH4. For catalytic reforming by char, the higher reaction temperature and the longer residence time, the lower tar content in fuel gas. Compared to thermal cracking, catalytic reforming of tar by char was more effective in tar removal efficiency and inhibition of carbon deposition, upgrading the quality of fuel gas. The researches indicated that the suitable operational conditions for tar removal by char in the FB two-stage gasification process were at reforming temperature of 1000 °C, and residence time above 0.9 s.

Electrochemical Investigation of Stainless Steel Cladded Carbon Steel Manufactured Via Powder Bed Selective Laser Melting

This study aims to investigate the electrochemical and corrosion properties of 316L-stainless steel cladded carbon steel manufactured using powder bed the selective laser melting (PB-SLM) technique in various environments. The PB-SLM technique involves localized melting of a thin layer of 316L-SS powder bed with Yb - fiber laser. Main parameters of the PB-SLM process such as particle size, particle size distribution, laser power, laser-scanning speed and layer thickness were selected to optimize the density of the cladded layer and the quality of metallurgical bond to the substrate. Using the optimized process parameters, carbon steel substrates were cladded with stainless steel of various thicknesses. Several mechanical and microscopic tests (viz. nano-indentation, X-ray diffraction, Scanning electron microscopy) were performed to characterize both the bulk properties of the stainless steel layer and the interface between the cladding and the substrate. Electrochemical and corrosion properties were tested via. open-circuit potential monitoring, electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP) in electrolytes with acidic to alkaline pH range and with increasing levels of chloride, simulating different application conditions. Scanning vibrating electrode technique was employed to study the galvanic corrosion properties of the stainless steel and carbon steel at the clad-substrate interface.

Seismic hazard assessment at micro level in Gandhinagar (the capital of Gujarat, India) considering soil effects

Gandhinagar City (the Capital of Gujarat, India) falls under Zone III on the seismic zoning map of India where an earthquake of magnitude 6 can be expected. It is a well established fact that the site amplification/ shaking and damage is large in soil covered areas. To estimate the effect of soil on ground motion and to estimate the strong ground motion parameters at surface, soil modeling and the ground response analysis have been conducted along uniformly distributed 14 boreholes drilled upto a depth of 50 m. The methodology is divided into three parts (i) Estimation of depth of Engineering Bed layer (EBL) (a layer with a shear wave velocity 400 m/s ≤ Vs ≤ 750 m/s, N value >80 and minimum soil variation below it) through soil modeling, (ii) Estimation of Ground Motion at EBL due to scenario earthquake at nearby active fault and (iii) Estimation of surface strong ground motion using 1D ground response analysis through SHAKE 2000 program. The EBL is found at a depth of 21–33 m (shallower in central part and deeper in northern and southern parts). The Near-Field scenario earthquake (Eq.) of magnitude Mw 6.0 has been considered along East Cambay Fault (normal fault, 60° dip) located at about ~ 20 km east and Far Field scenario Eq. of Mw 7.6 is considered along Kachchh Mainland Fault located ~270 km west. The Peak Ground acceleration (PGA) of 0.172–0.237 g have been estimated at surface due to near field earthquake scenario. The mean spectral acceleration maps for 0.1–0.4 s, 0.4–0.7 s, 0.7–1.0 s and 1.0–1.5 s have also been computed. The mean spectral acceleration for the period of 0.1–0.4 s has been varying from 0.330 g to 0.508 g, for period of 0.4–0.7 Sec, it has been varying from 0.151 g to 0.161 g and for period between 1.0 and 1.5 Sec, it has been found from 0.83 g to 0.09 g. The PGA is found increased by 5–38% in the first subsurface soil layer in Gandhinagar city. The PGA of the order of 0.059–0.072 g and peak Spectral acceleration of the order of 0.187–0.259 g have been computed (with predominant periods of ~0.1 s and 0.31 s) due to Far-Field Eq. scenario and are found less than Indian code. The PGA and Spectral acceleration (Sa) values are found higher than the Indian code in the period range of 0.1–0.4 s (one to four storey buildings) for Near Field Eq. Scenario.

Prediction of bed level variations in nonuniform sediment bed channel

In the present study, a numerical model, based on one-dimensional de Saint-Venant equations along with sediment continuity equation, is developed for prediction of bed levels in non-cohesive sediments in aggrading alluvial channels. One-dimensional, unsteady flow equations and sediment continuity equations are solved using ‘shock-capturing’, second order accurate, explicit MacCormack finite difference scheme while considering upstream and downstream boundary conditions in the channel. Series of experimental investigations have been undertaken for measurements of bed and water levels in an aggrading channel due to overloading of nonuniform sediments, extracted from the bed of Tapi River at Surat City, in a flume installed in Advanced Hydraulics Laboratory of SVNIT, Surat, India. A satisfactory coupling between the water flow and sediment flow has been achieved. The sediment continuity equation is used for the each size class to compute the volume of each size class after each time step at any computational node in the computational grid. The fractional bed and suspended load transport capacities for different size fractions have been computed using fractional transport laws for nonuniform sediments. The active bed layer concept has been implemented in finite difference scheme to consider the interaction and exchange of sediment and water flow near the mixing layer. The performance of developed numerical model has been satisfactorily verified with independent experimental data of nonuniform sediment bed. Also, consideration of sediment nonuniformity in computation of bed level variation has been demonstrated by comparing the results based on sediment transport functions of uniform and nonuniform sediments.

Microbial diversity of thermophiles with biomass deconstruction potential in a foliage-rich hot spring.

The ability of thermophilic microorganisms and their enzymes to decompose biomass have attracted attention due to their quick reaction time, thermostability, and decreased risk of contamination. Exploitation of efficient thermostable glycoside hydrolases (GHs) could accelerate the industrialization of biofuels and biochemicals. However, the full spectrum of thermophiles and their enzymes that are important for biomass degradation at high temperatures have not yet been thoroughly studied. We examined a Malaysian Y‐shaped Sungai Klah hot spring located within a wooded area. The fallen foliage that formed a thick layer of biomass bed under the heated water of the Y‐shaped Sungai Klah hot spring was an ideal environment for the discovery and analysis of microbial biomass decay communities. We sequenced the hypervariable regions of bacterial and archaeal 16S rRNA genes using total community DNA extracted from the hot spring. Data suggested that 25 phyla, 58 classes, 110 orders, 171 families, and 328 genera inhabited this hot spring. Among the detected genera, members of Acidimicrobium, Aeropyrum, Caldilinea, Caldisphaera, Chloracidobacterium, Chloroflexus, Desulfurobacterium, Fervidobacterium, Geobacillus, Meiothermus, Melioribacter, Methanothermococcus, Methanotorris, Roseiflexus, Thermoanaerobacter, Thermoanaerobacterium, Thermoanaerobaculum, and Thermosipho were the main thermophiles containing various GHs that play an important role in cellulose and hemicellulose breakdown. Collectively, the results suggest that the microbial community in this hot spring represents a good source for isolating efficient biomass degrading thermophiles and thermozymes.

A Metallographic Review of 3D Printing/Additive Manufacturing of Metal and Alloy Products and Components

Applications and examples of light and electron micrographs illustrating microstructures, which describe metallurgical phenomena in 3D printing/additive manufacturing of metal and alloy products and components, are presented along with extensive process and processing parameter descriptions and review. Examples include microstructures that have defined turbine blade fabrication and optimization over the past half century, including contemporary electron beam melting fabrication of turbine blade alloys and other novel microstructures and architectures, which result from layer by layer, non-equilibrium melt solidification and epitaxial growth involving powder bed laser and electron beam fabrication. Phase transformations and second-phase formation by rapid cooling in metal and alloy components fabricated by laser and electron beam melting technologies are illustrated for a range of high-temperature materials. Using a range of examples, the advantages of fabricating complex (especially porous) biomedical and related commercial products are described. Prospects for future developments of direct 3D metal and alloy droplet printing, as a key component of the digital factory of the future, are described. This technology is compared with more conventional solidification and powder bed layer building thermo-kinetics, especially in the context of large structure and component fabrication.

Post-tonsillectomy taste dysfunction: Myth or reality?

Lingual branches of the glossopharyngeal nerve (CN Ⅸ) are at risk of injury during tonsillectomy due to their proximity to the muscle layer of the palatine tonsillar bed. However, it is unclear how often this common surgery leads to taste disturbances. We conducted a literature search using PubMed, Embase, Cochrane Library, Google Scholar, PsychInfo, and Ovid Medline to evaluate the available literature on post-tonsillectomy taste disorders. Studies denoting self-reported dysfunction, as well as those employing quantitative testing, i.e., chemogustometry and electrogustometry, were identified. Case reports were excluded. Of the 8 original articles that met our inclusion criteria, only 5 employed quantitative taste tests. The highest prevalence of self-reported taste disturbances occurred two weeks after surgery (32%). Two studies reported post-operative chemical gustometry scores consistent with hypogeusia. However, in the two studies that compared pre- and post-tonsillectomy test scores, one found no difference and the other found a significant difference only for the left rear of the tongue 14 days post-op. In the two studies that employed electrogustometry, elevated post-operative thresholds were noted, although only one compared pre- and post-operative thresholds. This study found no significant differences. No study employed a normal control group to assess the influences of repeated testing on the sensory measures. Overall, this review indicates that studies on post-tonsillectomy taste disorders are limited and ambiguous. Future research employing appropriate control groups and taste testing procedures are needed to define the prevalence, duration, and nature of post-tonsillectomy taste disorders.

Flow pattern transition and coal beneficiation in gas solid fluidized bed with novel secondary distributor

Gas solid fluidized bed (GSFB) is an effective method of dry coal separation. In this study, porous sponge was introduced into a typical gas solid fluidized bed as secondary air distribution layer (PSFB) to stabilize the fluidized bed layer. The difference between PSFB and GSFB in flow pattern transition process was studied. Compared with GSFB, the minimum gas velocity and bed density fluctuation decreased while bed expansion ratio increased in PSFB. Furthermore, the distribution of bubble phase and emulsion phase were more homogeneous in PSFB. Under the operational conditions, the results of coal preparation in a PSFB showed that the ash content of clean coal was 10.25% .The probable error (E) was 0.095 g/cm3, indicating that PSFB could provide a novel way for a good performance of dry coking coal beneficiation.

Four-layer model for prediction of sand bed height in horizontal gas-liquid stratified flow

Gas-liquid stratified flow is the most vulnerable flow regime for sand deposition, owing to the low phase velocities that occur in this flow regime. A theoretical and experimental study is conducted for particle transport in horizontal gas-liquid-solid stratified flow with high particle concentrations.Experimental data are acquired for air, water and spherical glass beads flow with a solid particle concentration of 20,000 PPM. Two particle sizes are utilized, 45–90 μm and 425–600 μm, with superficial liquid velocities of VSL=0.05 and 0.1 m/s and superficial gas velocities of VSG=3.75, 6.7 and 8.6 m/s. Data are acquired for the total particle bed height, demonstrating that it reduces with increasing superficial gas velocity, while increasing with smaller particle size.A new four layer model for gas, liquid, moving bed and stationary bed is proposed for high particle concentrations greater than 10,000 PPM. The gas, liquid and solid particle continuity equations, along with the momentum equations for the gas, liquid and moving bed layers are solved simultaneously, where the stationary particle bed is treated as a boundary. The model enables prediction of the heights and velocities of all four layers. The model predictions for total particle bed height are compared with the experimental data showing a good agreement.

Measurement of the local material depth in a directly-heated pilot rotary kiln based on temperature fields

The heat and mass transfer processes in rotary kilns are greatly influenced by the depth of the material. A method is proposed for automatic measurement of the local material depth in a directly-heated pilot rotary kiln, based on temperature fields in the kiln cross section. By analyzing the motion behavior of the material and the periodic pattern of the temperatures profile, the material region and the gas region are qualitatively identified. A statistical variable is then proposed to estimate the average temperature of the active layer of the material bed, with which the central angle covered by the thermocouples through the material bed can be determined and thus the material depth be estimated using geometrical relationship. The effectiveness of the proposed measuring method for bed depth is tested on a directly heated pilot rotary kiln and compared with results of manual measurement. It is found that the proposed method has good accuracy (maximal error 7%) as well as good stability for all the fourteen testing cases. Results of this work can be used conveniently in the experimental study of rotary kiln process, without introducing any additional hardware.

3D metal printing technology: the need to re-invent design practice

3D printing or additive manufacturing is a novel method of manufacturing parts directly from digital model using layer-by-layer material build-up approach. This tool-less manufacturing method can produce fully dense metallic parts in short time, with high precision. Features of additive manufacturing like freedom of part design, part complexity, light weighting, part consolidation, and design for function are garnering particular interests in metal additive manufacturing for aerospace, oil and gas, marine, and automobile applications. Powder bed fusion, in which each powder bed layer is selectively fused using energy source like laser, is the most promising additive manufacturing technology that can be used for manufacturing small, low-volume, complex metallic parts. This review presents overview of 3D Printing technologies, materials, applications, advantages, disadvantages, challenges, economics, and applications of 3D metal printing technology, the DMLS process in detail, and also 3D metal printing perspectives in developing countries.

Bed-load transport rate based on the entrainment probabilities of sediment grains by rolling and lifting

A function for the bed-load sediment transport rate is derived. This function is obtained by using the entrainment probabilities of the rolling and lifted sediment grains, and by introducing two travel lengths, respectively. The predictions from the new bed-load function agree well with experimental results over the entire experimental range and show significant improvement over the commonly used formula for the bed-load transport rate. The new function shows that, in terms of contributing to the bed-load transport rate, the total entrainment probability of the sediment grains is a weighted summation of those for the lifted and rolling grains, rather than a simple addition of the two. The function is also used to predict the total entrainment probability, saltation length, and the bed layer thickness at a high bed-load transport rate. These predictions all agree well with the experimental results. It is found that, on average, the travel length for the rolling sand grains is about an order of magnitude less than that of the lifted grains.

Vibration Behavior and Reinforcement Effect Analysis of the Slab Track‐Subgrade with Mud Pumping under Cyclic Dynamic Loading: Full‐Scale Model Tests

Mud pumping occurring in the subgrade bed can gradually deteriorate the performance of the slab track‐subgrade, negatively affecting the comfort and safety of high‐speed railway. In this paper, a full‐scale model of the slab track‐subgrade was established to analyze the vibration behavior of the model in normal condition and before and after mud pumping reinforced, as well as the reinforcement effect of mud pumping using low‐viscosity epoxy resin. The research results show that the vibration acceleration and displacement and the settlement of the model in normal condition stabilize gradually with the increasing number of loading cycles. Under the upper layer of the subgrade bed saturated by water, mud pumping occurs in the subgrade bed as soon as the second loading stage reaches to 3.0 × 104 cycles, and the deterioration of mud pumping increases gradually with the increasing number of loading cycles. Moreover, a large volume of slurry composed of water and fine particles is squeezed out of the subgrade bed after the model is subjected to the second cyclic loading stage of 2.0 × 106 cycles, causing contact loss between the concrete base and the subgrade bed, which makes the acceleration and displacement of the concrete base increase abnormally compared with the model in normal condition, as well as the cumulative settlement of the subgrade bed. The model with significant mud pumping in the upper layer of the subgrade bed was reinforced by using low‐viscosity epoxy resin. This effectively controlled the abnormal acceleration and displacement of the concrete base and restored the support capability of the subgrade bed for the concrete base of the slab track structure.

Numerical simulation of the effect of bedding layer geometrical properties on the punch shear test using PFC3D

In this research the effect of bedding layer angle and bedding layer thickness on the shear failure mechanism of concrete has been investigated using PFC3D. For this purpose, firstly calibration of PFC3d was performed using Brazilian tensile strength. Secondly punch shear test was performed on the bedding layer. Thickness of layers were 5 mm, 10 mm and 20 mm. in each thickness layer, layer angles changes from 0o to 90o with increment of 25o. Totally 15 model were simulated and tested by loading rate of 0.016 mm/s. The results show that when layer angle is less than 50o, tensile cracks initiates between the layers and propagate till coalesce with model boundary. Its trace is too high. With increasing the layer angle, less layer mobilizes in failure process. Also, the failure trace is very short. It\'s to be note that number of cracks decrease with increasing the layer thickness. The minimum shear punch test strength was occurred when layer angle is more than 50o. The maximum value occurred in 0o. Also, the shear punch test tensile strength was increased by increasing the layer thickness.