Combination Of Densification Research Articles

Extrusion‐based additive manufacturing of alumina ceramics through controlled extrusion pressure

AbstractThe development of dense alumina ceramics through additive manufacturing necessitates the careful analysis of various parameters. The extrusion pressure during printing is a crucial but often overlooked factor in the literature. This study investigates the impact of extrusion pressure on the densification and mechanical properties of alumina ceramics. The primary objective is to analyze extrusion pressure to achieve superior physical and mechanical characteristics while maintaining minimal shrinkage. All other printing parameters were kept constant, and the extrusion pressure was varied from 1 to 2.85 bar during the extrusion‐based additive manufacturing of alumina green bodies. The printed and sintered samples were analyzed for linear shrinkage, density, compressive strength, and microhardness. The results indicate that an extrusion pressure in the 2.2–2.5 bar range leads to alumina ceramics with the best combination of densification and other mechanical properties. Additionally, the interparticle bonding mechanisms contributing to the improved properties of the alumina ceramics were examined. This study provides valuable insights into the role of extrusion pressure in the additive manufacturing process, underscoring its significance in achieving high‐quality alumina ceramics.

Effect of unilateral surface compression technique and heat treatment on industrial application performance of poplar

The utilization of unilateral surface compression technique offers significant advantages such as reduced volume loss of wood and energy consumption, making it highly promising for widespread applications. This work focused on fast-growing poplar (Ctrl) as research subject. The unilateral surface compression technique was employed to prepare compressed wood (USW), while superheated steam was utilized to suppress rebound effects (resulting in the formation of US＆HW). The results showed that the combination of densification and heat treatment technology significantly enhanced the application performance of wood. Compared to Ctrl, the densified area exhibited a significant reduction in the volume of cell cavities, with a stepped distribution evident on the VDP. Furthermore, heat treatment resulted in a decrease in the relative amount of hydroxyl in the wood, as well as a slight increase in crystallinity. This effectively reduced deformation in dense wood, resulting in a 20.02% reduction in its recovery rate, without causing excessive damage to the VDP. Additionally, Heat treatment resulted in a darker wood color, reduced glossiness, increased roughness, and further increase the water contact angle of the compressed wood. The mechanical performance of US＆HW achieved an excellent grade, with a score of 48, while all six processing performance grades of US＆HW exceeded Grade 3, surpassing those of both USW and Ctrl. The finishing performance of the US＆HW was good, although slightly lower than that of USW in terms of ball impact performance. And the adhesion, hardness and abrasion resistance indexes of the paint film meet the requirements of excellent products in the standard.

An experimental study of the contact mechanical behaviour of marble spheres under cyclic loading

A series of cyclic compression tests of marble spheres and scanning electron microscopy (SEM) imaging measurements were performed in this work. The cyclic compression tests of marble spheres reveal three different fracture types: Hertzian cracks, oblique fractures and multi-meridian fractures. The displacement of marble spheres with Hertzian cracks or oblique fractures in cyclic compression tests can be significantly larger than the displacement (0.31 mm) corresponding to sample breakage in monotonic compression tests. The SEM observations reveal that mineral fragmentation, plastic shear sliding and crack closure occur in the local contact area, resulting in obvious residual displacement. Hertzian cracks were produced by the combination of densification and shear strength degradation under cyclic loading. Typical two-stage behaviour of cumulative residual displacement and dynamic secant stiffness evolution with the number of cycles was clearly observed. The occurrence of Hertzian cracks or oblique fractures produced significant cumulative residual displacement. The present laboratory results also show that the increase in amplitude can result in a significantly larger cumulative residual displacement and that the number of cycles of marble sphere failure in meridian fracture significantly increases with an increase in the frequency of cyclic loading. The upper contact force ratio and amplitude ratio significantly influence the dynamic secant stiffness evolution. The dynamic secant stiffness of tests under amplitude ratios of 0.7 and 0.8 shows a clear decreasing trend after the initial decelerating stage, which may be related to the loosening and decohesion of mineral particles caused by local significant fragmentation.

Experimental study on the behaviour of granular column-treated soft clay under shear loading

ABSTRACT Compacted granular columns are frequently used to mitigate construction difficulties over soft soil deposits through a combination of densification, increasing load-bearing capacity and improvement in consolidation features. The behaviour of granular columns under vertical loading has been well recognised; however, this research is aimed to investigate the behaviour of granular column-reinforced soft soil subjected to shear stress. In this contribution, large-scale direct shear tests were performed, and the influence of undrained shear strength of clay, diameter of granular column and relative density of aggregates was examined. In general, the use of granular column has been shown to improve the shear resistance of the composite ground, which was found to be much significant at lower undrained shear strength of the soft clay. Increasing density of aggregates from Dr = 50% to 90% caused a large portion of the shear stress to be sustained by the accumulated friction of aggregates as the internal friction angle of the treated clay increased from 0 to 28°. In addition, test results revealed that the use of highly compacted column yields a lowered shear displacement at failure, which was indirect evidence of stiffness improvement of the composite ground.

Effects of drainage control on densification as a liquefaction mitigation technique

Ground densification is among the most popular techniques for liquefaction mitigation employed in practice. Yet, the effects of densification, especially in combination with strategies that enhance or inhibit drainage to or from the densified area, on the performance of the soil-foundation-structure system are not well understood. This paper describes dynamic centrifuge experiments to evaluate these effects, considering 3- and 9-story, moment-resisting frame structures with different embedment depths, founded on layered liquefiable soil deposits. The experiments compared structures mitigated with densification alone, and mitigated with a combination of densification and either prefabricated vertical drains (enhancing drainage) or a flexible impermeable latex barrier (inhibiting drainage) around the densified area. Ground densification tended to reduce the foundation settlement, although not to acceptable levels (based on limiting values typically considered in design and performance assessment), but amplified the drift and acceleration demands on the superstructure. The addition of a flexible impermeable barrier around the densified area did not have a notable influence on foundation settlement. However, it increased the excess pore pressures under the edges of the 3-story structure by inhibiting outward flow, amplifying its foundation rotation compared to the case with densification alone. In the case of the heavier and deeper, 9-story structure, adding a barrier around the densified zone restricted the locally inward flow from the adjacent loose soil. This helped reduce net pore pressures under the edges of the structure after strong shaking, foundation rotation, and seismic demand on the superstructure. Enhancing drainage around the densified zone, on the other hand, notably reduced permanent foundation settlement and rotation during all motions nearly to acceptable limits, but amplified accelerations, imposing additional seismic demands on the structure, which could lead to damage if not considered in design. These results demonstrate the importance of considering the structure's dynamic properties and force-deformation behavior, foundation and ground motion properties, and soil-structure interaction when planning the geometry of ground densification and drainage.

Simulation of wheel tracking test for asphalt mixture using discrete element modelling

This study investigated the simulation of wheel tracking test and the high-temperature rutting behaviour of an asphalt mixture by using the discrete element method (DEM). Based on the DEM software named as Particle Flow Code in three dimensions (PFC3D), a micromechanical model of an asphalt mixture composed of coarse aggregates, asphalt mastic, and air voids was built and a two-dimensional virtual wheel tracking test was simulated. Based on the virtual wheel tracking test, the distribution of displacement and contact forces within test specimen were analysed. It is proved that the built virtual wheel tracking test can capture the rutting deformation caused by the combination of densification and lateral flow deformation. It is also indicated that, within an asphalt mixture, the aggregate skeleton is the main bearing body for the compressive forces, while the compressive and tensile forces between aggregate and mastic are severer than that within asphalt mastic. It is important to guarantee the stability of the aggregate skeleton and the bonding strength between aggregate and asphalt mastic to resist rutting deformation.

REVIEW ON DENSIFICATION OF PALM RESIDUES AS A TECHNIQUE FOR BIOMASS ENERGY UTILIZATION

Due to the tremendous amount of palm biomass residues produced during the palm oil extraction from fresh fruit bunch (FFB), it is inevitable to harness these biomass energy sources to cope with the depletion of fossil fuels and increase in global energy demand scenarios. Densification is one of the favourable techniques to improve the storage and transportation of biomass fuels in order to prevent dumped areas adjacent to palm mills and to prevent from becoming another waste product. This article reviews comprehensively on how type of palm biomass, compaction pressure and temperature, binder, pre- and post-treatments affect the physical and combustion properties of the palm biomass briquettes produced. Based on the previous researches, generally it can be said that the type of palm biomass, the compaction pressure and temperature, and type of binder affect both the physical and combustion performance of densified palm biomass. However, the effect of particle size could be observed only on the physical characteristics of densified products, whereas the effect on the combustion properties remains unclear. In addition, treatments such as pyrolysis, dry and wet torrefaction (hydrothermal treatment), and steam explosion have potential to be applied during briquette production in order to improve the combustion properties. In this review article, it is also suggested that the combination of densification and followed by wet torrefaction will enhance the combustion properties of palm biomass briquettes.

A spatially distributed model for assessment of the effects of changing land use and climate on urban stream quality

AbstractWhile the effects of land use change in urban areas have been widely examined, the combined effects of climate and land use change on the quality of urban and urbanizing streams have received much less attention. We describe a modelling framework that is applicable to the evaluation of potential changes in urban water quality and associated hydrologic changes in response to ongoing climate and landscape alteration. The grid‐based spatially distributed model, Distributed Hydrology Soil Vegetation Model‐Water Quality (DHSVM‐WQ), is an outgrowth of DHSVM that incorporates modules for assessing hydrology and water quality in urbanized watersheds at a high‐spatial and high‐temporal resolution. DHSVM‐WQ simulates surface run‐off quality and in‐stream processes that control the transport of non‐point source pollutants into urban streams. We configure DHSVM‐WQ for three partially urbanized catchments in the Puget Sound region to evaluate the water quality responses to current conditions and projected changes in climate and/or land use over the next century. Here, we focus on total suspended solids (TSS) and total phosphorus (TP) from non‐point sources (run‐off), as well as stream temperature. The projection of future land use is characterized by a combination of densification in existing urban or partially urban areas and expansion of the urban footprint. The climate change scenarios consist of individual and concurrent changes in temperature and precipitation. Future precipitation is projected to increase in winter and decrease in summer, while future temperature is projected to increase throughout the year. Our results show that urbanization has a much greater effect than climate change on both the magnitude and seasonal variability of streamflow, TSS and TP loads largely because of substantially increased streamflow and particularly winter flow peaks. Water temperature is more sensitive to climate warming scenarios than to urbanization and precipitation changes. Future urbanization and climate change together are predicted to significantly increase annual mean streamflow (up to 55%), water temperature (up to 1.9 °C), TSS load (up to 182%) and TP load (up to 74%). Copyright © 2016 John Wiley & Sons, Ltd.

Dense Granular Columns in Liquefiable Ground. I: Shear Reinforcement and Cyclic Stress Ratio Reduction

AbstractThe installation of dense granular columns by various construction techniques can be used to mitigate liquefaction through a combination of densification, increase of lateral stresses, reinforcement, and drainage. The contributing mechanism of shear reinforcement is isolated and explored using nonlinear three-dimensional (3D) finite-element (FE) analysis. FE models representing both dry and saturated conditions were developed to evaluate cases with and without generation and dissipation of excess pore-water pressures. The shear stress and strain distributions between the granular columns and surrounding soil, and the level of shear stress reduction, were investigated for a practical range of treatment geometries, relative stiffness ratios, vertical stresses, and relative densities of the surrounding soil. A set of 10 acceleration time histories were used as input motions. The FE results show that granular columns undergo a shear strain deformation pattern that is noncompatible with the surrounding...

Dense Granular Columns in Liquefiable Ground. II: Effects on Deformations

AbstractDense granular columns can be used to mitigate liquefaction hazards through a combination of densification, increases in lateral stress, reinforcement, and drainage effects. Three-dimensional (3D) nonlinear dynamic finite-element analyses are used to examine the effectiveness of dense granular columns for reducing liquefaction-induced deformations in the event that the triggering of liquefaction in the native soils is not prevented. The finite-element analyses consider unit cells with dense granular columns (improved case) and without granular columns (unimproved case). Parametric analyses are used to isolate aspects related to the different improvement mechanisms. The parametric studies consider a range of area replacement ratios, shear modulus ratios, diameter of granular columns, liquefiable soil depth, hydraulic conductivity, surface pressures, slope angle, penetration resistances in the native soil, and spatial variations in those penetration resistances. A set of 10 acceleration time histori...

Combined densification and pulsed electric field treatment for selective polyphenols recovery from fermented grape pomace

Abstract The aim of this study is to assess a new process for the valorization of fermented grape pomace using pulsed electric fields (PEF). The combination of densification and PEF treatment was applied on grape pomace of low relative humidity, without any addition of conductive liquid. The kinetics of extraction and the composition of polyphenols were evaluated throughout the subsequent hydro-alcoholic extraction at different temperatures. Optimal parameters of PEF treatment (field strength E = 1.2 kV·cm − 1 ; energy input W = 18 kJ·kg − 1 ; density ρ = 1.0 g·cm − 3 ) increased the content of total polyphenols regardless of the temperature of extraction. The ratio of total anthocyanins to total flavan-3-ols at 20 °C was equal to 7.1 and 9.0 for control and PEF treated modalities, respectively. These results demonstrate the selective nature of PEF treatment in anthocyanin extraction, and thus reveal new possibilities to produce extracts with different biochemical compositions. Industrial relevance This study examines the feasibility of densification combined with PEF pre-treatment of relatively low humidity grape pomace for the enhancement of bioactive compounds extraction. The concentration of total phenolic compounds obtained after PEF treatment showed that the use of this technique is relevant for an industrial use, since solvent amount and extraction time can be reduced. Moreover, the selective nature of PEF opens the opportunity to produce extracts of different biochemical compositions. This process is an alternative to conventional pre-treatments of raw material (e.g. dehydration and grinding), which have impacts on product quality and are more energy consuming.

Study on the supply capacity of crop residue as energy in rural areas of Heilongjiang province of China

Abstract Heilongjiang is the most northeastern province of China. The climate of Heilongjiang consists of very cold winters, leading to large energy demands for space heating by local residents. Rich food crop yields in Heilongjiang results in large amounts of crop residues. To fully accommodate rural energy demand and facilitate the effective utilization of crop residues, this study builds a mathematical model of supply capacity of crop residues as energy, then, based on the data from a field survey and literature review, calculates the local annual effective heat demands for living, the supply rates for effective heat of different crop residue utilization patterns, and the supply capacities of crop residues as energy in rural areas of Heilongjiang. Results show that the supply capacity of traditional direct burning of crop residues is less than 1, indicating that direct burning of crop residues cannot fully supply rural living heat demands. The supply capacity of densification is more than 1.6, indicating that introducing densification can not only achieve full supply for rural living heat demands, but also result in a large proportion of crop residues remaining for other uses. Because part of the crop residues is converted to products other than gas, dry distillation can only supply 55% of the rural living heat demands. Introducing efficient technologies of crop residue utilization for energy in rural areas of Heilongjiang can make the available amount of energy from crop residues larger than the amount of energy demand. This study found that the combination of densification and dry distillation of crop residues can be used as a high-efficiency centralized supplement of living heat, achieving multiple benefits such as use of alternatives to fossil fuel energy, economic development, environment protection, and improvement in quality of life.

Effect of Temperature on Densification and Deformation Behaviour of Pure Aluminium Powders Processed by Equal Channel Angular Densification and Pressing

Abstract In this study, a dense bulk material was produced from pure aluminum powders by the equal channel angular densification (ECAD) and the equal channel angular pressing (ECAP) method. The combination of densification and ECAD/ECAP tests were carried out at temperatures of 50 °C, 100 °C, and 200 °C, a pressing speed of 1 mms−1, and a pressure in the range of 10–30 metric tons. By using these parameters, for the first time pure aluminum powders were successfully densified into fully bulk materials without additional sintering process. After the ECAD/ECAP tests, the specimens were characterized regarding microstructure, grain size, hardness, and density. The mean grain size was remarkably decreased with an increasing ECAP pass number. With the application of the ECAD/ECAP process, the severe plastic deformation entails that the particles are consolidated into fully dense materials at much lower temperatures and shorter times, as compared to the conventional sintering process. Finally, determining the effective ECAP temperature was very important to control the nano-scaled microstructure, hardness, and density, repectively.

Impact of the Combination of Densification and Thermal Modification on Dimensional Stability and Hardness of Poplar Lumber

With a view to evaluating the impact of the combination of densification and thermal treatment on dimensional stability and surface hardness, poplar (Populus lasiocarpa Oliv.) lumber was densified under three compression ratios (10, 18, and 25%), three press temperatures (130, 150, and 170°C), and two pressure holding times (15 and 35 min). It was subsequently thermally treated at three temperatures (180, 190, and 200°C) and three exposure times (1.5, 2.5, and 3.5 h). Density, density profiles, water-soaked radial (thickness) swelling, and surface hardness were examined. The results showed that the density of poplar was increased by 8–24% due to densification. Compared to the densified specimens, the average water-soaked radial swelling was reduced by 43% through thermal treatments. Compared to the nondensified and non-thermally treated specimens, the maximum water-soaked radial swelling was reduced by 38% after thermal treatment at 200°C for 3.5 h. When the compression ratio of 10, 18, or 25% was applied for the densification, the average surface hardness was increased from 18.9 to 27.1, 34.6, or 43.9 MPa, respectively. These hardness values are similar to or greater than that of birch, which is commonly used for hardwood flooring. It was concluded that the combination of densification and thermal treatment could convert the low-grade poplar into high-value products with improved dimensional stability and surface hardness.

Development of an Elastoviscoplastic Microstructural-Based Continuum Model to Predict Permanent Deformation in Hot Mix Asphalt

Permanent deformation in hot mix asphalt is caused by a combination of densification (decrease in volume and hence increase in density) and shear deformation. The primary objective of this paper is to develop an elastoviscoplastic model that accounts for the influence of important microstructure properties such as anisotropy and damage on permanent deformation. The model incorporates a yield surface based on the Drucker-Prager function that is modified to capture the influence of stress state on the material response. Also, parameters that reflect the directional distribution of aggregates and damage density in the microstructure are included in this yield surface model. The elastoviscoplastic model is converted into a numerical formulation and is implemented in finite element (FE). The FE model is used in this study to simulate experimental measurements under different confining pressures and strain rates.

Decomposition of Volatile Organic Compounds at Low Concentrations Using Combination of Densification by Zeolite Adsorption and Dielectric Barrier Discharge

The decomposition of toluene at very low concentrations (10–20 ppm) using a combination of densification by zeolite adsorption and dielectric barrier discharge (DBD) was investigated. The characteristics of toluene decomposition using DBD under open and closed-loop flow conditions were determined. Under the closed-loop gas flow condition, a high decomposition ratio (70–93%) and a high energy efficiency [8–19 g/(kW h)] were achieved for the adsorbed toluene (63% of the initial amount) by DBD treatment even at a high flow rate of 150 L/min. Also, by the periodic operation of adsorption/DBD treatment, it was demonstrated that DBD treatment regenerated the honeycomb sheet containing zeolites for subsequent adsorption. The usefulness of this method for the decomposition of hazardous materials at low concentrations was shown.

Combined Densification and Thermo-Hydro-Mechanical Processing of Wood

AbstractThe process of heating and compressing wood to improve its properties or reform it to a new shape has been known for decades. Such improvements are usually accompanied by “shape memory,” where the deformation produced by compression is not permanent, and the material recovers when re-moistened and heated. The combination of densification and a thermo-hydro-mechanical (THM) treatment can transform wood into a new material with improved mechanical properties, decreased sensitivity to moisture, increased durability, and no shape-memory effects. This article presents the principles of combined densification and THM processing, the products and experimental results, the origin of the shape-memory effect and its elimination by THM treatment, and the potential use of THM-processed densified wood in construction applications.

希薄揮発性有機物のゼオライト吸着による濃縮とバリア放電の組合せによる除去

A new scheme of removing volatile organic compounds(VOCs) at low concentration, using a combination of densification by a zeolite adsorption with a barrier discharge, has been tested and demonstrated to be effective. VOCs were first adsorbed in a honeycomb-shaped sheet containing zeolites as an adsorbing agent, and then desorbed and destroyed using a barrier discharge between electrodes, which were separated by the honeycomb-shaped sheet and dielectric barriers. After a proof-of-principle experiment to demonstrate the principle of the scheme, four different types of tests were conducted to quantitatively assess its usefulness. An extrapolation to a real size system was made from the obtained experimental results.

Abnormal grain growth of sputtered CuNi(Mn) thin films

The evolution in both stress and microstructure was investigated on sputtered Cu0.57Ni0.42Mn0.01thin films of 400 nm thickness during the first temperature cycle up to 550 °C. Samples from stress–temperature measurements up to various maximum temperatures were analyzed by x-ray diffraction, scanning and transmission electron microscopy, and Auger electron spectroscopy. The columnar grains with lateral diameters of about 20 nm in the as-deposited state coarsen to about 400 nm above 300 °C. Probably due to the impurity (Mn) drag effect, the coarsening occurs by abnormal grain growth rather than by normal grain growth, starting near the film–substrate interface. The stress development results from a combination of densification due to grain growth and plastic stress relaxation.