Dense Walls Research Articles

Direct numerical simulation of flow over dissimilar, randomly distributed roughness elements: A systematic study on the effect of surface morphology on turbulence

Direct numerical simulations of flow over fourteen dense rough walls with varying geometry are conducted. The effect of a departure from same-size element roughness on turbulence statistics is studied, and the correlation of the roughness function with wall-normal fluctuations at the roughness crest is examined.

Titanium Foams Processed Through Powder Metallurgy Route Using Lubricant Acrawax as Space Holder Material

In the present work titanium foams have been synthesized using acrawax as the space holder material. Acrawax has generally been used as a lubricant for easier compaction of aluminium alloy powders. This study deals with the use of this space holder material in the form of beads for creating pores in titanium metal matrix. Acrawax facilitates the formation of continuous dense cell walls which is difficult to obtain using ordinary space holder materials. Moreover, acrawax is compressible in nature and it facilitates the formation of better and uniformly sized pores. Titanium foams have been synthesized utilizing acrawax in two different sizes. The effect of using differently sized acrawax on the cell walls and mechanical properties has also been carried out in this study.

Grain morphologies and microstructures of laser melting deposited V-5Cr-5Ti alloys

A laser melting deposition (LMD) technique has been applied to fabricate thin wall V-5Cr-5Ti samples. By applying a scanning speed of 400 mm/min, laser powers of 1200W, 1400W, 1600W, and 1800W, and scanning strategies of single directional scanning and dual directional scanning, full dense thin wall samples have been successfully prepared. Microstructures at the bottom region of walls mainly consist of coarse columnar grains, showing a 〈100〉 fiber texture. Microstructures in the middle and at the top regions of walls mainly consist of fine columnar grains or equiaxed grains, showing random textures. Columnar dendritic growth takes place for columnar grains. The columnar dendrites grow epitaxially from parent grains, following one [100] axis closest to the heat flux direction. However, the integral growth directions of columnar grains are opposite to the heat flux direction. Including a small deviation of one [100] axis from heat flux direction, the growth space of columnar dendrites also counts for the success in competitive growth for columnar grains. Deposition height, laser power, and scanning strategy show significant effects on the grain structure evolutions of thin wall samples, due to their effects on the temperature gradient. As the deposition height increases, columnar to equiaxed transitions (CETs) have been observed for all samples. The CETs happen faster for higher laser power, and for dual directional scanning compared to single directional scanning. Due to the differences in local composition caused by microsegregation, clusters containing lath-like precipitates are observed to delineate the dendrites. The effects of processing parameters on microstructures can be represented by a metric of volumetric energy density. A decrease of energy density will lead to CETs.

Manufacturing of thin wall structures in AlSi10Mg alloy by laser powder bed fusion through process parameters

Laser powder bed fusion (LPBF) process allows to manufacture customized metal porous 3D parts known to have many interesting combinations of physical and mechanical properties. Therefore, the minimum resolution obtainable by this process is of high importance in the design of porous functional parts e.g. thin walls. Knowledge of the relationship between process parameters and material employed is fundamental to obtain these kinds of structures with LPBF. A series of experiments were carried out with a laser-melting system with laser power up to 200 W and a spot of 100 μm to analyze the influence of the manufacturing strategy in the construction of thin walls in AlSi10Mg alloy. The results showed that it is possible to have well defined dense thin walls using appropriate building strategies, providing also useful information for the design rules definition of the LPBF process. The results also showed that the energy density is not able to provide information on the complexity that involves the melt pools formation and propagation. A mathematical model was also developed to build well defined thin walls directly through the process parameters and to reduce the mismatch between as-designed and as-manufactured thin wall structures. The verification of such model was made building thin walls in AlSi10Mg and then comparing them to the as-designed structures.

Preliminary isolation and morphological observation of Enterocytozoon hepatopenaei infecting the shrimp Penaeus vannamei

PDF HTML阅读 XML下载 导出引用 引用提醒 南美白对虾肝肠胞虫的分离及形态学观察 DOI: 作者: 作者单位: 江苏省海洋水产研究所, 江苏 南通 226007 作者简介: 乔毅(1987-),男,助理工程师,主要从事水生动物病害学研究.E-mail:qiaoyishou@yeah.net 通讯作者: 中图分类号: S945 基金项目: 江苏省重点研发计划（现代农业）项目（BE2017384）；江苏省海洋水产研究所青年科学基金项目（SQ201705）；江苏省渔业科技项目（Y2017-020）；2018年农业生态环境保护项目（171821104022292002）；江苏省中央引导地方科技发展专项资金项目（YDZX20173200001267）. Preliminary isolation and morphological observation of Enterocytozoon hepatopenaei infecting the shrimp Penaeus vannamei Author: Affiliation: Jiangsu Institute of Oceanology and Marine Fisheries, Nantong 226007, China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了研究江苏地区感染南美白对虾（，EHP）的形态学特点，分析与国外报道的差异性，本研究以江苏地区感染肝肠胞虫的南美白对虾肝胰腺组织为研究材料，通过蔗糖密度梯度离心等方法进行肝肠胞虫初步分离纯化，构建一种肝肠胞虫荧光染色检测方法，显微观察肝肠胞虫的孢子形态结构。结果发现感染江苏地区南美白对虾的肝肠胞虫孢子主要分布在35%~40%浓度的蔗糖层面，可推算其密度为1.15~1.17 g/mL。荧光显微镜下可见孢子椭圆或圆形，呈亮蓝色，孢子微小但可计数，显微观察可见肝肠胞虫孢子大小约为1.7 μm×0.9 μm，外壁上有大量白色瘤状物，疑似胞壁蛋白，孢子表面布满细小褶皱，孢子具有一个细胞核，极丝4~6圈，细胞壁由一相对薄的电子透亮的孢子内壁和电子致密的孢子外壁组成。结论认为江苏地区南美白对虾肝肠胞虫的形态结构与国外报道的吻合，本研究建立的肝肠胞虫分离纯化、荧光染色方法以及取得的肝肠胞虫形态学资料可为其检测和研究提供参考。 Abstract:is a new species of microsporidia found to be affecting shrimp culture. Previous studies have shown that shrimps infected with grow slowly. In recent years, slow growth has been observed in Enterocytozoon hepatopenaei infection has been reported. To study the morphological characteristics of in Jiangsu Province and interpret the differences in context of the reports from other studies conducted abroad, this study used Penaeus vannamei cultured in Jiangsu Province as the research material. Preliminary isolation and purification of through sucrose density gradient centrifugation was performed. A method of diagnosing using Fluorescent Brightener 28 staining was established and the spore morphology was observed under a microscope. The results showed that the spores of were mainly distributed along the sucrose gradient of 35%-40%, and their buoyant density was 1.15g/mL-1.17g/mL. The spores were elliptical or round, bright blue, and small, but countable under the fluorescence microscope. The spores were approximately 1.7 μm×0.9 μm. The spore surface is covered with small folds and there is a large amount of white nodules present on their outer wall, which may be wall protein; the cell wall is composed of a relatively thin, electron-transparent inner wall and an electron dense spore wall. The spores have a nucleus, and 4-6 coils of the pole filament. The morphological structure of in Jiangsu was consistent with the reports abroad. The methods of isolation, purification, and fluorescent staining developed, as well as the morphological data of obtained in this study provide reference for diagnosis and research. 参考文献 相似文献 引证文献

Nanostructured Al <sub>2</sub>O <sub>3</sub>-YAG-ZrO <sub>2</sub> Ternary Eutectic Components Prepared by Laser Engineered Net Shaping

The present work proposed a novel 3D printing approach for fabricating ternary eutectic ceramics (Al2O3-YAG-ZrO2, or AYZ in short) using laser engineered net shaping (LENS) technique. Highly dense (≥ 98%) thin wall components with refined eutectic microstructures were successfully fabricated. The as-fabricated ceramic eutectics mainly consist of cellular eutectics with three phases interpenetrated. In each deposited layer, the solidified microstructure changes from planar to cellular along building direction. The evolution of characteristic dimension of microstructure can be well interpreted using Jackson-Hunt relationship. Irregular interpenetrating to regular fibrous eutectic structure transition occurs at boundary region of LENSed specimens, primarily due to much higher solidification rate. The texture of Al2O3 // YAG // ZrO2 is recognized at the interior region of LENSed eutectic part along building direction, but gradually tilts from central to edge due to change of cellular growth direction. The LENSed AYZ samples exhibit almost isotropic property, and have mechanical performances comparable to those fabricated using conventional direction solidification methods.

Effects of laser shock peening on mechanical behaviors and microstructural evolution of brass

The mechanical behaviors and the microstructures of brass induced by laser shock peening (LSP) are investigated systematically. The compressive residual stresses (CRS) and the micro-hardness in surface layers are performed using X-ray residual stress tester and hardness tester respectively. The microstructures of the deformation layers are characterized using transmission electron microscopy (TEM). It is found that the CRS and the micro-hardness increasing are accompanied by improving laser pulse energy. The deformation layer induced by 4.5J LSP is divided into top surface layer, SPD layer and MPD layer according to the microstructures and CRS. The equiaxed grain size in the top surface layer after 4.5J LSP impacts is approximately 20 nm to 30 nm. The grain refinement process during LSP impacts can be described as follows: (i) dislocation structures are generated by strain and strain rate induced laser shock wave; (ii) original coarse grains subdivide into sub-grains with dislocation tangles (DTs) and dense dislocation walls (DDWs) forming at their grain boundaries; (iii) dynamic recrystallization (DRX) in sub-grain boundaries takes place due to the dislocation array transitions; (iv) new grain boundaries are formed in sub-grains, then they are subdivided into nano-scale equiaxed grains with the accumulation of plastic deformation.

The Usability of Boric Acid as an Alternative Foaming Agent on the Fabrication of Al/Al2O3 Composite Foams

Pure Al and alumina (2, 5, 10 wt.% Al2O3)-added Al composite foams were fabricated through powder metallurgy technique, where boric acid (H3BO3) is employed as a new alternative foaming agent. It is aimed to determine the effects of boric acid on the foaming behavior and cellular structure and also purposed to develop the mechanical properties of Al foams by addition of Al2O3. Al and Al composite foams with porosity fraction in the range of 46-53% were achieved by sintering at 620 °C for 2 h. Cell morphology was characterized using a combination of stereomicroscope equipped with image analyzer and scanning electron microscopy. Microhardness values were measured via using Vickers indentation technique. Quasi-static compression tests were performed at strain rate of 10−3 s−1. Compressive strength and energy absorption of the composite foams enhanced not only by the increasing weight fraction of alumina, but also by the usage of boric acid which leads to formation of boron oxide (B2O3) acting as a binder in obtaining dense cell walls. The results revealed that the boric acid has outstanding potential as foaming agent in the fabrication of Al and Al composite foams by providing improved mechanical properties.

Effects of torsional deformation on the microstructures and mechanical properties of a CoCrFeNiMo0.15 high-entropy alloy

The effects of torsional deformation on the microstructures and mechanical properties of a CoCrFeNiMo0.15 high-entropy alloy have been investigated. The torsional deformation generates a gradient microstructure distribution due to the gradient torsional strain. Both dislocation activity and deformation twinning dominated the torsional deformation process. With increasing the torsional equivalent strain, the microstructural evolution can be described as follows: (1) formation of pile-up dislocations parallel to the trace of {1 1 1}-type slip planes; (2) formation of Taylor lattices; (3) formation of highly dense dislocation walls; (3) formation of microbands and deformation twins. The extremely high deformation strain (strained to fracture) results in the activation of wavy slip. The tensile strength is very sensitive to the torsional deformation, and increases significantly with increasing the torsional angle.

Promotion of the alginate gelling method for preparing Al2O3 honeycomb ceramics

ABSTRACTIn this work, Al2O3 honeycomb ceramics with unidirectionally aligned channels were fabricated by the ionotropic gelation process of alginate/Al2O3 suspensions. By heating the bottom of the suspension container during the gelation step, the heat energy conducted upward from foot to the top surface of the slurry, which has shortened the gelation time from 48 to 10 h and improved efficiency dramatically. Meanwhile, as the heating temperature increased from 25 to 40°C, the porosity of Al2O3 honeycomb ceramics remained unchangeable with the pore size decreasing from 163 to 79 μm for the increasing opportunities for forming capillaries in the primary membrane. By the integrated effect of unidirectional pore channels and dense pore walls, both the compressive strength and water permeability of the sintered samples were higher than those of Al2O3 foam ceramics.

Influence of hydrogen on dislocation self-organization in Ni

The influence of hydrogen on the evolution of the deformation microstructure in Ni at the same specific macroscopic strain has been determined for the first time. The evolution of the microstructure was accelerated by hydrogen as evidenced by the formation of smaller dislocation cells and dense dislocation walls compared to only dislocation cells in the absence of hydrogen. This enhanced evolution is described in terms of the hydrogen-enhanced localized plasticity mechanism.

The evolution of deformation microstructure in electron beam melted Ta-2.5W alloy during cold rolling

The evolution of deformation microstructure in electron beam melted Ta-2.5W alloy was investigated. The morphology of microbands appear different in different reduction levels. The microbands are relatively straight at low to medium strain and can cross the grain boundary. They become wavy when the reduction reaches 70%. The microbands are parallel with rolling direction when the reduction is up to 90%. The average inclination angles between microbands and rolling direction is about 35° at 20% reduction and get smaller and smaller with increasing strain. EPBs are developed when the reduction is 20%. Most of grains contain one or two groups of EPBs occupying almost the whole grain interiors when the reduction is larger than 30%. The EPBs are fragmented, diffused and curved in the early stages of development. When the reduction reaches 40%, the EPBs become more well-developed and homogeneous. The dislocations within EPBs tend to rearrange themselves with increasing strain in a sequence, from tangled dislocations, followed by parallel dislocations and finally into dislocation nets. The evolution of microbands is related with both the cross-slip of dislocations and the splitting of high dense dislocation walls.

Experimental modelling of copper foams processed through powder metallurgy route using a compressible space holder material

The present work is focused on the processing of open cellular copper foams through space holder technique without the use of binders. In this work, moderate pressures were used during the cold compaction of the powders. The main objective was to obtain dense cell walls by limiting the use of binders and use a compressible and lubricant type of space holder material. It has been shown in this study that the use of high compaction pressure helps to decrease/limit the quantity of binder required and this, in turn, yields relatively dense cell walls necessary for better mechanical strength of foams. Using 2N factorial method, mathematical models have been developed to express the final porosity and pore size as functions of the various processing parameters viz compaction pressure, sintering temperature/ time and space holder content. The most significant sintering parameters influencing the porosity and pore size of the processed foams have also been found out.

Recovery Phenomenon During Annealing of an As-Rapidly Solidified Al Alloy

It has been well documented that recovery occurring in metals/alloys produced via solid-state quenching involves only annihilation of supersaturated vacancies. Interestingly, in the present study, we observed completely different mechanisms underlying recovery during annealing of an Al-Zn-Mg-Cu (7075 Al) alloy processed via liquid-state quenching, i.e., rapid solidification (specifically melt spinning herein). The as-melt-spun alloy consists of refined grains containing tangled dislocations inside the grains. Following annealing at 393 K (120 °C) for 24 hours, refined grain structure was still retained and grain sizes essentially remained unchanged, but subgrains separated by dense dislocation walls were generated at grain interiors, with a much lower density of dislocations at subgrain interiors than that in the as-melt-spun 7075 Al alloy and dislocation arrays inside some subgrains. The microstructural evolution suggests the absence of recrystallization and the occurrence of recovery primarily via the annihilation and rearrangement of dislocations and the formation of subgrains. Based on the stored energy in dislocations in, and the annealing temperature of, the as-melt-spun 7075 Al alloy, the recovery phenomenon was analyzed and discussed in detail.

Current-Induced Generation and Synchronous Motion of Highly Packed Coupled Chiral Domain Walls.

Chiral domain walls of Neel type emerge in heterostructures that include heavy metal (HM) and ferromagnetic metal (FM) layers owing to the Dzyaloshinskii-Moriya (DM) interaction at the HM/FM interface. In developing storage class memories based on the current induced motion of chiral domain walls, it remains to be seen how dense such domain walls can be packed together. Here we show that a universal short-range repulsion that scales with the strength of the DM interaction exists among chiral domain walls. The distance between the two walls can be reduced with the application of the out-of-plane field, allowing the formation of coupled domain walls. Surprisingly, the current driven velocity of such coupled walls is independent of the out-of-plane field, enabling manipulation of significantly compressed coupled domain walls using current pulses. Moreover, we find that a single current pulse with optimum amplitude can create a large number of closely spaced domain walls. These features allow current induced generation and synchronous motion of highly packed chiral domain walls, a key feature essential for developing domain wall based storage devices.

Sustained Dye Release Using Poly(urea-urethane)/Cellulose Nanocrystal Composite Microcapsules.

The aim of this study is to develop methods to reinforce polymeric microspheres with cellulose nanocrystals (CNCs) to make eco-friendly microcapsules for a variety of applications such as medicines, perfumes, nutrients, pesticides, and phase change materials. Surface hydrophobization treatments for CNCs were performed by grafting poly(lactic acid) oligomers and fatty acids (FAs) to enhance the dispersion of nanoparticles in the polymeric shell. Then, a straightforward process is demonstrated to design sustained release microcapsules by the incorporation of the modified CNCs (mCNCs) in the shell structure. The combination of the mCNC dispersion with subsequent interfacial polyurea (PU) to form composite capsules as well as their morphology, composition, mechanical properties, and release rates were examined in this study. The PU microcapsules embedded with the mCNC were characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The morphologies of the microcapsules were characterized by optical microscopy (OM) and scanning electron microscope (SEM). The rupture stress and failure behavior of the microcapsules were determined through single-capsule compression tests. Oil-soluble Sudan II dye solution in mineral oil was utilized as a model hydrophobic fill, representing other latent fills with low partition coefficients, and their encapsulation efficiency was measured spectroscopically. The release rates of the encapsulated dye from the microcapsules were examined spectroscopically by both ethanol and 2-ethyl-1-hexanol medium at room temperature. The concentration of released dye was determined by using UV-vis absorption spectrometry (UV-vis). The mCNC embedded poly(urea-urethane) capsules have strong and dense walls, which function as excellent barriers against leakage due to their extended diffusion path length and ensure enough mechanical strength from rupture for handling or postprocessing.

Microstructure and mechanical properties of a high strength Cu-Ni-Si alloy treated by combined aging processes

High strength Cu-Ni-Si alloys were potential elastic conductive materials due to their high strength and high electrical conductivity. To address the trade-off between strength and electrical conductivity, a combined aging process has been developed to enhance the properties of a Cu-6.0Ni-1.0Si-0.5Al−0.15Mg-0.1Cr alloy after an initial thermo-mechanical heat treatment. The microstructure evolutions of the studied alloys were investigated by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The mechanical and physical properties were evaluated through hardness measurements, tensile test and conductivity test. The results demonstrated that a hardness value of 381 HV, an ultimate strength of 1155.8 MPa, an elongation of 3.5%, and an electrical conductivity of 25.2%IACS were achieved after an appropriate combined aging process. Cold rolling led to the formation of a dense dislocation wall as a result of dynamic interactions among the dislocations and precipitates. During the second stage of aging, nanoscale precipitates formed in the first stage slowly coarsened and effectively pinned dislocations motion. The combined aging process increased the hardness and strength, without sacrificed the electrical conductivity. This work provided an effective route for balancing the strength and electrical conductivity of copper alloys.

The effect of interstitial carbon on the mechanical properties and dislocation substructure evolution in Fe40.4Ni11.3Mn34.8Al7.5Cr6 high entropy alloys

A systematic study of the effects of up to 1.1 at. % carbon on the mechanical properties and evolution of the dislocation substructure in a series of a high entropy alloys (HEA) based on Fe40.4Ni11.3Mn34.8Al7.5Cr6 is presented. Transmission electron microscopy (TEM), synchrotron X-ray diffraction (XRD) and atom probe tomography (APT) were used to show that all the alloys are single-phase f.c.c. random solid solutions. The lattice constant, determined from synchrotron XRD measurements, increases linearly with increasing carbon concentration, which leads to a linear relationship between the yield strength and the carbon concentration. The dislocation substructures, as determined by a TEM, show a transition from wavy slip to planar slip and, at higher strains, and from cell-forming structure (dislocations cells, cell blocks and dense dislocation walls) to non-cell forming structure (Taylor lattice, microbands and domain boundaries) with the addition of carbon, features related to the increase in lattice friction stress. The stacking fault energy (measured via weak-beam imaging of the separation of dislocation partials) decreases with increasing carbon content, which also contributes to the transition from wavy slip to planar slip. The formation of non-cell forming structure induced by carbon leads to a high degree of strain hardening and a substantial increase in the ultimate tensile strength. The consequent postponement of necking due to the high strain hardening, along with the plasticity accommodation arising from the formation of microbands and domain boundaries, result in an increase of ductility due to the carbon addition.

Mechanical properties enhanced by deformation-modified precipitation of θ′-phase approximants in an Al-Cu alloy

The influence of large pre-deformation on the age hardening behaviors, tensile properties and precipitate characteristics in an Al-Cu alloy during artificial ageing was investigated using mechanical property measurements and electron microscopy. Room-temperature rolling of Al-Cu alloy with a thickness reduction of 80% plus a subsequent artificial ageing can result in a strength increase of 35% without sacrificing ductility compared with an alloy that is peak–aged using a conventional heat treatment process (T6). A large quantity of dislocations that accumulated during cold-rolling was retained in the alloy after post-ageing at 150°C. Although dense dislocation walls and dislocation tangles that exist in cold-rolled Al-Cu alloys were expected to cause micro-structural heterogeneity, the plate-shaped precipitates on the {001}Al planes exhibited an exceptionally uniform distribution. Atomic-scale angular dark-field scanning transmission electron microscopy (ADF-STEM) revealed these precipitates are θ′–approximants with a crystal structure similar with the well–known tetragonal θ′ phase but with the body-centered position not fully occupied by Cu. In addition, the precipitate sizes were considerably refined as compared to the θ′ precipitates that were formed in the T6 peak-aged alloys. The microstructure–property relationships in the alloy are discussed to explain the observations. Our results suggest the deformation-modified precipitation may play a vital role in achieving better strength-ductility synergy.

Fabrication, characterization and controlled release properties of oat protein gels with percolating structure induced by cold gelation

Cold-set oat protein isolate (OPI) gels possessing a percolating network structure were successfully prepared using a glucono-δ-lactone (GDL) induced acidification method. The polymer-like percolating structures were established by active OPI monomers as small building block units through abundant cross-linking points. By increasing the GDL concentration, more intra-floc linkages and greater particle volume fractions were created at the supramolecular level, resulting in a dense rough gel wall with superior mechanical properties. In particular, at a 10% GDL content the gel was generated at the OPI isoelectric point (IEP). This OPI gel had a compact network structure with small pores and a thick wall, with an excellent water holding capacity (90%) and comparable mechanical strength (30 kPa) to egg white gel (22–32 kPa). Also, the cold-set OPI gels could resist acidic juice and pepsin digestion, which protected both α-amylase enzyme activity and the viability of probiotics in harsh gastric conditions. The in vitro release experiment demonstrated that OPI gels had the capacity to prevent the premature release of bioactive compounds in simulated gastric fluids, and yet still allowed their gradual release in a simulated intestinal environment where they normally would be absorbed. A convenient and non-toxic method to prepare OPI gels with superior performance has been described. These gels have the potential to act as delivery vehicles for sensitive compounds in food and non-food applications.