Bed Layer Research Articles

Impact force of post-fire debris flows over erodible beds

After wildfire events, water repellent soil is often found in the subsurface layer of channel bed in the burnt area. Debris flows generated from burnt basins and ensuing entrainment of the channel bed pose imminent threat to infrastructure and human lives. However, the fundamental interaction mechanisms of debris flow overriding water repellent bed and resulting impact force on debris-resisting barriers have yet to be elucidated. In this study, physical flume experiments are conducted to simulate post-fire debris flows overriding and entraining a sand bed with varied wettability. Compared to a wettable bed, water repellent sediment exhibits a tremendous increase in the erosion depth and subsequent impact force on the barrier. The test results demonstrate that debris flows overriding water repellent sediment can be particularly hazardous and the effects of water repellency need to be captured by the design criteria of debris resisting barriers in burnt basins.

Kinematic mode of operation of potato harvester auger

The digging work parts of modern potato harvesters, when working on loamy soils with low humidity, do not meet the agrotechnical requirements. Modern machines should perform pruning, lifting, and moving the potato bed layer to the separating organs without unloading and collapsing with the least energy consumption, losses, and damage to tubers. The authors proposed combined digging work parts with passive plowshares and active augers. The purpose of the study is to substantiate the operating mode of the potato harvester auger. The basic principles and methods of classical mechanics, mathematical analysis, and statistics were used in this study. Based on theoretical studies, analytical dependences for determining the operating mode of the auger are obtained. To ensure pruning, lifting, and moving of the tuberous, the kinematic mode indicator should be in the range of 4.08 - 4.15.

Production of ultrapure biomethane from stratified bed in non-adiabatic and non-isothermal plate pressure swing adsorption

Biomethane is a renewable and clean source of energy, which can be employed to abate the greenhouse gases emissions and support the sustainable developments. Novel plate pressure swing adsorption mediated by a stratified bed containing UiO-66 followed by un-treated biomass-based adsorbent was used for production of ultrapure biomethane from biogas mixture of 30 % CO2 (balanced by CH4). Plate PSA design was proposed due to the exchangeable heat between the adsorption and desorption bed in non-isothermal/non-adiabatic conditions. Breakthrough experiments of CH4 and CO2 for individual and layered bed were conducted to understand the gases behavior in the different systems. The results were also used to determine the appropriate range of PSA operating parameters i.e., the adsorption pressure and adsorption/blowdown time. A quadratic model was built to optimize the pressure and CO2 content in the biogas feed for maximum bio-CH4 purity in the adsorption line. The results revealed that the introduction of UiO-66 layer which was positioned before the un-modified biomass adsorbent improved bio-CH4 purity to 99.99 % and recovery of 69.6 % under the adsorption pressure of 2 bar at room temperature. The optimum point to achieve the ultrapure bio-CH4 was located at pressure of 2 bar, CO2 content of up to 50 % and adsorption/blowdown time of 4 min. In this work, a new layering strategy consisting of different strata of un-treated biomass-based adsorbent and microporous UiO-66 adsorbent was introduced for bio-CH4 purification using plate PSA under non-adiabatic/non-isothermal conditions.

Fused Deposition Modelling of Polymer Composite: A Progress.

Additive manufacturing (AM) highlights developing complex and efficient parts for various uses. Fused deposition modelling (FDM) is the most frequent fabrication procedure used to make polymer products. Although it is widely used, due to its low characteristics, such as weak mechanical properties and poor surface, the types of polymer material that may be produced are limited, affecting the structural applications of FDM. Therefore, the FDM process utilises the polymer composition to produce a better physical product. The review's objective is to systematically document all critical information on FDMed-polymer composite processing, specifically for part fabrication. The review covers the published works on the FDMed-polymer composite from 2011 to 2021 based on our systematic literature review of more than 150 high-impact related research articles. The base and filler material used, and the process parameters including layer height, nozzle temperature, bed temperature, and screw type are also discussed in this review. FDM is utilised in various biomedical, automotive, and other manufacturing industries. This study is expected to be one of the essential pit-stops for future related works in the FDMed-polymeric composite study.

Analysis of the kinetic energy recovery behind a tidal stream turbine for various submergence levels

Tidal turbines are commonly deployed at sea sites with water depths of up to 50 m to ease their deployment and quick maintenance operations. In these relatively shallow water depth conditions, the vertical expansion of tidal stream turbine wakes is restricted by the proximity of the rotor blades to the bottom bed and free-surface layer. These physical constrains can lead to changes in the flow mechanisms that drive momentum recovery behind the turbines, e.g. limiting the vertical fluxes of velocity. Understanding how the wake recovers depending on the submergence ratio is of utmost importance to designing the future multi-row tidal turbine arrays. Here, we adopt high-fidelity Large-Eddy Simulations (LES) with an Actuator Line Method (ALM) to represent the turbine's rotor to analyse the mean flow and transport equation for mean kinetic energy (MKE) behind a single bottom-fixed tidal turbine for four water depth values. Our results show that the close proximity of the turbine blade tip to the free-surface can notably constrain the wake expansion, with very shallow conditions leading to a limited contribution to the MKE replenishment of the turbulent momentum exchange over the vertical direction. Conversely, under such shallow conditions, the horizontal flux of MKE is enhanced over the lateral boundaries of the downstream wake. Our study evidences that the ratio of water depth to turbine diameter plays a relevant role in future tidal arrays and needs to be correctly accounted for in numerical models to provide reliable results.

Mathematical Simulation of Iron Ore Fines Sintering Process with Solid Fuel Segregation Distribution and Corresponding Heat Pattern Study

The fuel segregation distribution sintering process, with a high fuel dosage in upper layer and a low fuel dosage in bottom layer of the sintering bed, was studied to handle uneven heat distribution problems in the conventional iron ore sintering process. A mathematical simulation method was adopted to contrastively study the fuel segregation distribution sintering process and the conventional iron ore sintering process. The accuracy of the model was verified through the sintering experiments. In addition, different heights of the upper and bottom sintering beds were discussed to assess the fuel segregation distribution sintering technology. In contrast to the conventional iron ore sintering process, the temperature evolution in the sintering bed using the fuel segregation distribution sintering technology tended to be more reasonable and the heat accumulation in the upper bed increased, which meant that the melt quantity index increased from 2178 to 2387 K·min−1, and cooling rate decreased from 360 to 199 K·min−1. The drawbacks of the conventional iron ore sintering process, such as the heat shortage in upper bed and excess heat in lower bed, were therefore improved, which was also proven to promote the sinter quality.

Laser Powder Bed Fusion of Intermetallic Titanium Aluminide Alloys Using a Novel Process Chamber Heating System: A Study on Feasibility and Microstructural Optimization for Creep Performance

A laser powder bed fusion process operating at elevated temperatures is introduced capable of fabricating crack-free and dense intermetallic titanium aluminide alloy specimens as well as demonstrator components using a base plate heating up to 900 °C and a unique heating system of the uppermost powder bed layer up to 1200 °C. Two so-called 4th generation alloys, TNM and TNM+, were used for this study. The microstructure and its evolution during subsequent heat treatments were investigated and explained by employing scanning electron microscopy, hardness testing, X-ray diffraction, differential scanning calorimetry and thermodynamic equilibrium calculation. Selected specimens were subjected to creep tests at 750 °C. The microstructures after processing consist of extraordinarily fine lamellar γ-TiAl/α2-Ti3Al-colonies with globular γ and βo-TiAl grains for both the TNM and TNM+ alloy, exhibiting a microstructure gradient from the last consolidated powder layer down to the starting layer due to cellular reaction, which increases the amount of globular γ and βo at the boundaries of the γ/α2-colonies. During annealing in proximity to the γ-solvus temperature, banded microstructures might form, as the α-grain size is only partially controlled by heterogeneously distributed γ/β-phase, which stems from the process-related Al loss. Additionally, the occurrence of thermally-induced porosity is investigated. Optimizing the microstructure to a homogenized, almost fully lamellar microstructure, involved annealing in the β-single phase field region and led to improved creep properties. Finally, TNM demonstrator components with complex geometries, such as aero engine blades and turbocharger turbine wheels, are fabricated by employing the novel laser powder bed fusion process.

Prediction of the Influence of Printing Parameters on the Residual Stress Using Numerical Simulation

Abstract Fused Deposition Modeling is an additive manufacturing technology that is used to create a wide range of parts and applications. Along with its benefits, there are some challenges regarding the printed parts’ mechanical properties, which are associated with printing parameters like layer thickness, printing speed, infill density, printing temperature, bed temperature, infill pattern, chamber temperature, and printing orientation. One of the most crucial challenges in additive manufacturing technology is the residual stress, which significantly affects the parts like fatigue life, cracks propagation, distortions, dimensional accuracy, and corrosion resistance. Residual stress is hard to detect in the components and sometimes is costly to investigate. Printing specimens with different parameters costs money and is time-consuming. In this work, numerical simulation using Digimat-AM software was employed to predict and minimize the residual stress in printed Acrylonitrile Butadiene Styrene material using Fused Deposition Modeling technology. The printing was done by choosing six different printing parameters with three values for each parameter. The results showed a significant positive correlation between residual stress and printing temperature and infill percentage and a negative correlation with layer thickness and printing speed. At the same time, we found no effect of the bed temperature on the residual stress. Finally, the minimum residual stress was obtained with a concentric infill pattern.

Breeding of Indian Spiny Loach, Lepidocephalichthys thermalis (Valenciennes, 1846) under Captive Conditions

The breeding of Indian spiny loach, Lepidocephalichthys thermalis was standardized under laboratory conditions at Madhavarm campus, Tamil Nadu Dr Jayalalithaa Fisheries University, Chennai, Tamil Nadu, India during May–August, 2014. Three different conditions were maintained in the breeding tanks which included gravel bed at the bottom with floating aquatic plants, gravel bed at the bottom without plants and soft sand layer bed at the bottom without plants. Spawning took place in the tanks provided with gravel bed at the bottom with and without plants. The eggs were transparent, adhesive and found attached to the plants and gravels. The incubation period ranged from 20–30 h at a temperature of 29.5°C. The newly hatched larvae were transparent with an average body length of 2 mm when observed microscopically. On day 1, larvae were thread- like with two external gill filaments on either side of the head and a pair of pectoral fin and a rounded caudal fin. On day 5, larvae developed four external gill filaments on either side of the head with prominent eyes, dark pigmentation with an average total length of 3.5 mm. On day 10, larvae had well-developed dorsal fin and a pair of anal fin. On day 10, larvae had an average total length of 13 mm with two pairs of barbels. Four weeks old larvae resembled the adults with an average total length of 20 mm. It is concluded that Indian spiny loach could be successfully bred in captive conditions by providing specialized spawning environment.

Artificial neural network and semi-empirical modeling of industrial-scale Gasoil hydrodesulfurization reactor temperature profile

The sulphur content of the desulfurization reactor product is strongly related to the severity of the reaction, which is determined by the reactor bed temperatures. In this study, the potential of neural network and semiempirical regression models to estimate temperature variation in industrial-scale gasoil HDT reactor was examined to achieve improved prediction ability. The reactor consists of 4 beds with 10 temperature indicators to control and monitor the temperature. Model developing Inlet temperature, H2/HC ratio, LCO flowrate, cracked gasoline flowrate, and straight run gasoil flowrate as input layer parameters and bed section outlet temperature as output layer was used. A database with 283 different data was built using daily records of the HDS process from an Iranian refinery. Feedforward backpropagation algorithm with learngdm learning function was used to develop ANN models. The number of neurons in the hidden layer varied between 7–13 to find the most reliable network. The optimum ANN models were selected for reactor temperature profiles on the trial-and-error method. The performance of designed models was tested by computing root mean square error (RMSE), and average absolute deviation (AAD). Comparing the neural network model and regression models, the artificial neural network model is the best model for the reactor bed temperature prediction. The value of AAD for temperatures sensors 1 to 10 in the artificial neural network model obtained 0.128, 0.094, 0.091, 0.1, 0.032, 0.067, 0.052, 0.031, 0.086, and 0.062 respectively, which show good agreement between the actual data and the artificial neural network predicted data for temperature profile in the length of the reactor.

Methods of Additive Manufacturing for Dental Co-Cr Alloys: Systematic Review

Additive manufacturing is a popular method of producing items directly from digital models through a layer-by-layer material build-up process. To evaluate the Current State of Knowledge on Dental Co-Cr Alloy Additive Manufacturing Techniques. Innovative additive printing technologies have made it possible to produce intricate dental components customized for each patient. This study investigated the manufacturing method (build orientation and process parameters), post-processing techniques, and metallic powders utilized in dental applications (stress relieving, surface finishing). The databases PubMed, Science Direct, Mendeley, and Google Scholar were used to carry out an electronic search. A manual search of pertinent article citations was also carried out; inclination angle, stress relieving, heat treatment, cobalt-chromium, selective laser melting, selective laser sintering, and powder bed fusion, dentistry were some of the keywords utilized. Although this publication tries to contain the most recent study from the previous eleven years (2010–2021), and to explain the materials powders and metal used in dental applications. A cutting-edge technique called additive manufacturing uses a layer-by-layer approach to material build-up to produce things directly from digital models. It is missing a tool, a manufacturing process that produces fully thick metallic components quickly and with good precision. Qualities of additive aspects of production such component design flexibility, part complexity, light- weighting, component consolidation, and functional design are generating specific interest in the additive fabrication of metal for use in automotive, marine, oil & gas, and aerospace industries during powder bed fusion, each layer of the powder bed is only partially fused employing a laser or electron beam as an energy source, the recent and most promising additive manufacturing technologies utilized to produce intricate, low-volume, tiny metallic parts. By using computer-aided design (CAD) technology, recent developments in digital dentistry have changed dental offices and dental laboratories, by utilizing 3D printing because precise metal framework fitting and technique faster.

Spatiotemporal evolution of excess pore pressures in a silty seabed under progressive waves during residual liquefaction

Both transient and residual pore pressure responses are induced as ocean waves propagate over a silty seabed. In this study, the spatiotemporal evolution of excess pore pressure in a silty seabed under progressive waves was physically modelled in a large wave flume. Three typical stages were identified in the process of residual liquefaction via flume observations, including quasi-elastic, intensive build-up of residual pore pressure, and continuous liquefaction stages. During the initial quasi-elastic stage before the liquefaction of the silt bed, the transient pore pressure can be well predicted by the analytical solution based on poro-elastic theory. After that, the residual pore pressure builds up intensively to its maximum value, even in the case that the transient pore pressure is nearly negligible at deep soil layer. Once the residual liquefaction occurs, the poro-elastic theory becomes invalid for describing the pore pressure response. The residual liquefaction is not simultaneously induced within the entire bed, but gradually progresses downward from the shallow layer of the silt bed to deeper. The pore pressure amplitude is significantly amplified after the silt liquefies, while no amplitude-amplification was observed within the un-liquefied silt. An amplification ratio (ζ) is proposed to characterize the amplification effect and distinguish the onset of residual liquefaction. The value of ζ during the continuous liquefaction stage is found to be one order of magnitude larger than that in the quasi-elastic stage. Comparisons with the existing centrifuge tests further indicate that the critical cyclic stress ratio for the silt bed is much smaller than that for the sand bed, implying the silt bed is more prone to residual liquefaction.

Topographic thresholds for gully head formation in badlands

AbstractGully erosion is a particularly damaging process which is not yet sufficiently understood and parameterized. Gully head topographic threshold relative to Hortonian runoff have been studied in cropland, rangeland and forest. This study extends such modelling approach to badlands. Different badlands (eight sites) have been studied in the Mediterranean environment in Italy and Spain, characterized by diversified climatic, lithological, and geological settings under different anthropogenic conditioning. Many badlands have been characterized by their specific human history in addition to their geomorphological properties. Land use, as part of the human history, strongly affected many badland formation and development, through extremely impacting land exploitation (usually overgrazing). The effect of geological and geomorphological processes are usually particularly well visible. While the weakening effect of joints is confirmed, the different geological layer bedding orientation with respect to the slope aspect generates a different development of badland morphologies and different values of gully head thresholds values (as shown in two badlands sites on the same geological material and climate.The selection of Curve Number values, at the base of the introduction of land use into the gully head thresholds, has been more objectively defined in order to reduce arbitrariness in threshold application. The study additionally revises some of the physical basics behind the gully head threshold concept, requiring a description of the soil resistance in terms of frictional and cohesive components. This implies the explicit inclusion of rock fragment into the grain size distribution, which cannot be limited to fine grains. It results into an enriched threshold formulation that allows to describe the condition for gully head initiation and retreat as the result of the tradeoff between the frictional and cohesive components of the soil resistance forces. Eventually, the gully head threshold concept is confirmed and extended to include badlands.

Pre-rig mobilization hazard evaluation in offshore oil and gas prospect drilling: A case study of TM field, offshore Niger Delta

TM Field, located offshore Niger Delta in the Gulf of Guinea (Nigeria), has been evaluated for potential drilling hazards prior to the drilling of a proposed oil well. This is in a region where potential hazards that could inhibit successful drilling exercise have not been adequately studied. The study adopted the modern technique of offshore geohazard evaluation that relies mainly on suites of geophysical and shallow geological investigations which include ocean bathymetry using multi-beam echo sounder, side-scan sonar, sub-bottom profiler, magnetic, and 2D-high resolution seismic reflection surveys. The results were integrated to draw inferences about the risk potential of the field. From the bathymetric survey, water depths were found to range from 345 m to 650 m LAT, with seabed relief being 305 m. Water depth at the proposed well location was found to be approximately 450 m and the seabed was found to slope in the northwestern direction. Seafloor gradient was computed as 0.05 across the whole area. Two shallow sub-surface stratigraphic units, labelled A and B, were delineated. Unit A was directly beneath the seafloor and seemed to be composed mainly of clayey/silty sand. Its thickness ranged from 6 m to 70 m across the study area. Unit B appeared to be a layer of sand and its total thickness was not fully delineated. Observable kinks and displacements at the flanks of seabed undulations/depressions on sub-bottom profiler sections suggested that the depressions may be fault-controlled. On the map generated from the marine magnetic data, a magnetic fault was delineated and this appeared to be coincident with the shallower of the two buried faults on the cross-line seismic section cutting through the proposed well-head location. Interpreted seismic reflection data presented this fault as being inactive. Most of the faults mapped, especially the buried ones, appeared to be inactive except a few. Regions with mapped amplitude anomalies are to be avoided during rig-mobilization operations. Though engineering conditions are expected to vary vertically since layers occur as intercalation, significant lateral variation is not expected within uniform layers of bed. Risk of punch-through associated with clayey formation is expected to be low because the geologic layers are not uniformly and entirely clay. The proposed well-head location was found to be free of potential hazard sources.

Performance Evaluation of Force Transducer for the Observation of Sediment Entrainment in Rapidly Varied Flows

Abstract Direct measurement of forces within the rough bed layer have been limited by previous spatial-averaging shear force studies. A highly sensitive force transducer assembled with a target sphere was used to measure and record the instantaneous three-dimensional forces of sediment at incipient motion. In the current study, a laser Doppler anemometer, ultrasonic displacement meter, and a force transducer accompanied by video recordings were used to experimentally investigate the incipient motion of sediment. The developed experimental setup have the potential to resolve and improve fundamental classical hypotheses regarding the incipient sediment motion. Experiments conducted in a large recirculating flume verified that the force transducer detects instantaneous forces at incipient motion under varies hydrodynamic conditions. Depth time series, instantaneous horizontal, vertical, and lateral forces are presented for dam-break and tidal breaking bores. Evidence suggests that the uplift vertical force plays an important role in destabilizing and in the incipient motion of particles. A sudden decrease in horizontal force was observed in tidal breaking bore due to flow reversal; however, a rapid rise was observed due to initial impact of dam-break bore. Bore velocity seems to have a larger effect on dam-break force than bore height. Furthermore, lateral force has the least influence during tidal breaking bore, while sediment particles are subjected to additional lateral force during dam-break bore.

STUDY OF THE GAS DYNAMIC OPERATION OF SINTERING MACHINES AT SINTER PLANT No. 5 OF PJSC MMK

A brief equipment description of the Sinter Plant No. 5 at PJSC MMK. The technical and economic inefficiency of the recirculation system based on the direct selection of waste gases from eight vacuum chambers of the sinter machines is shown. The expediency of connecting the vacuum chambers of the recirculation system to the collectors of sinter machines is substantiated. The influence of successive connection of these vacuum chambers to collectors on the gas-dynamic and technological parameters of the sinter machine has been studied. The accompanying factors were taken into account, such as climatic conditions (work with raw iron ore materials in warm time and relatively dry in cold), work with a gradually increasing mix layer bed at sinter machines. The technical inexpediency of using parallel collectors of sinter machines and the expediency of installing a sectional collector are substantiated using the example of a sinter machine with a sintering area of 312 m2 . For a generalized assessment of the influence of the sintering area, the width and length of the sinter machine on the gas-dynamic and technological parameters, the gas-dynamic model of the sintering process was adapted, and the corresponding analysis was carried out. The data obtained can be used in modernization of the existing sinter machines, including Sinter Plant No. 5, and in the design of the new ones.

Experimental and numerical investigation on the mechanical characteristics and failure mechanism of cracked coal & rock-like combined sample under uniaxial compression

The coal and rock bear the load together considering the fact that underground mining is usually operated in layered beds, which results in that the mechanical responses of the coal-rock combined body (CRCB) are distinct from those of pure coal or rock mass. However, the engineering structure of CRCB is mostly in a state of crack development, and therefore it is necessary to investigate the mechanical behavior and failure mechanism of CCRB containing cracks for assessing structural safety and disaster prevention. In this paper, a series of uniaxial compression tests were carried out on cracked coal-rock combined (CCRC) samples, and the strength and deformation characteristics, acoustic emission (AE) features and failure process of samples with various crack inclination angles were analyzed. Based on the stress state of coal and rock section near the interface, the constraint effect was founded and the variation of strength characteristics for the materials on both sides of the interface was discussed. Furthermore, a failure criterion was proposed to predict whether cracks would penetrate the interface, and the results of theoretical analysis agree well with the failure characteristics of the CCRC samples observed in the test. Then a numerical model was developed in PFC2D and its accuracy was verified. The failure pattern is further numerically investigated and the failure criterion is verified again based on the simulated micro-crack evolution behavior near the interface. Besides, the mechanical characteristics and failure features of CCRC sample with respect to different crack lengths, positions and inclination angles are also studied, which helps understand the mechanical behaviors and failure characteristics of CCRB structure more comprehensively.

Islands of the Tectonic Origin in the Shatt Al-Arab River, Southern Iraq

Several factors control the formation of river islands, such as tectonic factors, sedimentation, erosion, and human activities. This research is concerned with islands in the Shatt Al-Arab channel, which are likely to be traced back to tectonic factors in their formation. The islands of the Shatt Al-Arab River are distributed along its axis starting from the islands of Sindbad and Muhammadiyah, 15 km to the north of the city center of Basra, to the islands of Shatit, Al-Dawasir and Minauhi, 70 km south of the city center of Basrah. This study area is part of the Mesopotamia Plain, southern Iraq. The fieldwork period extended from the beginning of September 2012 to June 2013, which included making subsurface sections (longitudinal and transverse) of the bottom of the Shatt Al-Arab channel using the Sub-bottom profile Strata box device, imaging the topography of the river bottom in a side scan sonar, collecting the bottom sediments by a grab sampler. The volumetric analysis method uses the Master Sizer device based on the Folk classification to calculate the volumetric gradient of sediments. The study showed that the tectonic factor has a prominent role in the growth island Maino and as a result of the presence of sub-surface structures for the structure of the Siba, which appeared to affect the subsurface layers of the river bed near the island as it appeared in the survey sections of the Strata box device. There are some islands that more than one factor emerged as a reason for their formation and development, as in the islands of Muhammadiyah and Umm al-Rasas, where tectonic and sedimentary factors interfered in their formation and development due to the influence of sub-surface structures as well as the influence of nearby rivers such as the Karma and Karun Rivers.

Accumulative Plastic Deformation of the Improved Completely Weathered Granite Subgrade in High-Speed Railway

The improvement and reuse of completely weathered granite (CWG) with poor engineering properties for backfilling embankments can help protect the environment and bring great economic benefits. The embankment of high-speed railways demands an extremely low additional subgrade settlement under long-term dynamic loads. To analyze the applicability of the improved CWG used for subgrade filling, a series of laboratory dynamic triaxial and field cyclic loading tests were carried out. On the basis of the test results, a calculation model of accumulative plastic strain considering the dynamic stress ratio and the cement content was established. Using the proposed model and the numerically calculated dynamic stress, the accumulative plastic deformation of an embankment filled with improved CWG under various driving conditions was calculated and discussed. The variation of accumulative plastic deformation of the improved CWG with loading cycles could be described by a power function. The dynamic stress level had a significant influence on the accumulative plastic strain, and the strain in the bottom layer of the subgrade bed was greatly attenuated. Accordingly, most of the accumulative plastic deformation attenuation occurred within the depth range of the subgrade bed. The final total accumulative plastic deformations of the embankment were less than 2 mm (5 mm for the limit value) after 4 million times of high-speed train loadings, proving that the improved CWG can be used for subgrade filling. The influence of the axle load on accumulative plastic deformation was more significant than that of the train speed. The proposed calculation model of the accumulative plastic strain could provide valuable reference for similar railway engineering.

The effect of 3D printing parameters on the shape memory properties of 4D printed polylactic acid circular disks: An experimental investigation and parameters optimization

Additive manufacturing (AM) using Fused deposition modeling (FDM) is one of the advanced fabrication processes which allows for fabricating sophisticated parts with high speed and low cost. Four-dimensional (4D) printing is a novel technology that emerged with the addition of time dimension to three-dimensional (3D) printing of smart materials. In this technology, the structure that 3D printed transforms over time, leading to deformation. The primary purpose of the 4D printing process is to control deformation type and amount during the process, but little research has been done on the controllability of the 4D printing process. This study presents a model to control the amount of deformation by examining the effect of FDM printing method parameters on polylactic acid (PLA) material using response surface methodology (RSM) for the first time. These parameters include layer height, print speed, nozzle temperature, and bed temperature. The results showed that the effect of the parameters on the height of the recovered conical shape were printing speed, layer height, bed temperature, and nozzle temperature, respectively. In the following, using the central composite design (CCD), high-order models were predicted to calculate the process control conditions, i.e., control the type and amount of deformation with a minor error compared to the experimental results. The maximum amount of conical deformation with a height of 17.63 mm was obtained by achieving optimal printing conditions. With the help of controllability obtained from the effective parameters, two shapes, such as a bowl and a straw hat, were created.