Considerable Volume Fraction Research Articles

Influence of raster angle on tensile properties of FDM additively manufactured plates made from carbon reinforced PET-G material

Tensile properties of thin plate specimens made from short carbon fiber reinforced PET-G material are experimentally evaluated for various raster angles (printing directions). In additive manufacturing (AM), raster angle is recognized as one of the key printing parameters which strongly influences the strength and stiffness of the final part. The relatively high average value of ultimate tensile strength was obtained for specimens printed with the 0? raster angle, compared to the value obtained for specimens printed with the 90? raster angle - 52.2 MPa and 25.4 MPa, respectively. Similarly, noticeably higher average value of modulus of elasticity was obtained for specimens printed with the 0? raster angle, compared to the value obtained for specimens printed with the 90? raster angle - 4752 MPa and 1569 MPa, respectively. Scanning electron microscopy (SEM) was used for analysis of specimens? fracture surfaces. SEM images revealed considerable volume fraction of voids (porosity). ?he porosity, together with weak bonding between two adjacent rasters, could be one of key factors for poor tensile properties of samples printed with rasters perpendicular to direction of load application (90? raster angle).

Experimental study of the temperature effect on two-phase flow properties in highly permeable porous media: Application to the remediation of dense non-aqueous phase liquids (DNAPLs) in polluted soil

The remediation of aquifers contaminated by viscous dense non-aqueous phase liquids (DNAPLs) is a challenging problem. Coal tars are the most abundant persistent DNAPLs due to their high viscosity and complexity. Pumping processes leave considerable volume fractions of DNAPLs in the soil and demand high operational costs to reach cleaning objectives. Thermally enhanced recovery focuses on decreasing DNAPL viscosity to reduce residual saturation. The oil industry has previously applied this technique with great success for enhanced oil recovery applications. However, in soil remediation, high porous media permeabilities and product densities may invalidate those techniques. Additionally, the impacts of temperature on coal tar's physical properties have not been thoroughly discussed in available literature. Here, we investigated how coal tar's physical properties, the capillary pressure-saturation curve and the relative permeability of two-phase flow in porous media depend on the temperature and flow rate experimentally. Drainage and imbibition experiments under quasi-static (steady-state) and dynamic (unsteady-state) conditions have been carried out at 293.15 K and 323.15 K in a 1D small cell filled with 1 mm homogeneous glass beads. Two different pairs of immiscible fluids have been investigated, coal tar-water and canola oil-ethanol. Results demonstrated similar trends for temperature effect and values of fluid properties for both liquid pairs, which backs up the use of canola oil-ethanol to model coal tar-water flow. It was found that there is no temperature effect on drainage-imbibition curves or residual saturation under quasi-static conditions. In dynamic conditions, the DNAPL residual saturation decreased by 16 % when the temperature changed from 293.15 K to 323.15 K. This drop was mainly linked to decreasing viscous fingering, as well as the appearance of wetting phase films around the glass beads. Both phenomena have been observed only in dynamic experiments. A high enough pumping flow rate is needed to generate dynamic effects in the porous medium. Ethanol and oil's relative permeabilities also increase with temperature under dynamic measurement conditions. Our findings indicate that flow rate is an important parameter to consider in thermal enhanced recovery processes. These effects are not taken into account in the classically used generalized Darcy's law for modeling two-phase flow in porous media with temperature variation.

The formation mechanism of pores and unbonding in the Al2O3/Al2O3 joints brazed by 50Bi2O3–35B2O3–15ZnO glass

50Bi2O3–35B2O3–15ZnO (mol. %) glass referred to as Bi50 glass, was used to braze Al2O3 ceramics. The phase transformations and wettability of the Bi50 glass on Al2O3 substrates at different temperatures were investigated. The results showed that the chemical compatibility of Bi50 glass and Al2O3 substrates at 650 °C was excellent. However, Al2O3/Al2O3 joints having a considerable volume fraction of pores and unbonding were obtained when the joining procedures were carried out by a one-step brazing method. Based on the experiments and simulation results, the prime determinants responsible for the presence of the pores and unbonding within the brazing joints can be divided into two aspects: (i) the intrinsic causes leading to the formation of closed pores (ii) the external factors causing the failure of pores and glass separation. Ultimately, an advanced joining procedure named two-step brazing was proposed, and joints nearly free of defects were acquired.

A mesoscale stress model for irradiated U 10Mo monolithic fuels based on evolution of volume fraction/radius/internal pressure of bubbles

Abstract Fracture near the U 10Mo/cladding material interface impacts fuel service life. In this work, a mesoscale stress model is developed with the fuel foil considered as a porous medium having gas bubbles and bearing bubble pressure and surface tension. The models for the evolution of bubble volume fraction, size and internal pressure are also obtained. For a U 10Mo/Al monolithic fuel plate under location-dependent irradiation, the finite element simulation of the thermo-mechanical coupling behavior is implemented to obtain the bubble distribution and evolution behavior together with their effects on the mesoscale stresses. The numerical simulation results indicate that higher macroscale tensile stresses appear close to the locations with the maximum increments of fuel foil thickness, which is intensively related to irradiation creep deformations. The maximum mesoscale tensile stress is more than 2 times of the macroscale one on the irradiation time of 98 days, which results from the contributions of considerable volume fraction and internal pressure of bubbles. This study lays a foundation for the fracture mechanism analysis and development of a fracture criterion for U 10Mo monolithic fuels.

Influence of Heat Treatments on the Microstructural Evolution and Resultant Mechanical Properties in a Low Carbon Medium Mn Heavy Steel Plate

In this study, the microstructural evolution and resultant mechanical properties in a low carbon medium Mn heavy steel plate were investigated in detail. The results show that the introduction of medium manganese alloy design in the heavy steel plate has been shown to achieve the outstanding combination of strength, ductility, low-temperature impact toughness, and strain hardening capacity. It has been found that the austenite phase mainly displays at martensitic lath boundaries and shows lath shape for the heat treating at 873 K (600 °C) for 1 to 10 hours or 893 K (620 °C) for 2 hours, and not all the austenite phase obeys the K–S or N–W orientation relationship with respect to abutting martensitic lath. Although the microstructure in the steel after heat treating at 873 K (600 °C) for 1 to 10 hours is similar to each other, the resultant mechanical properties are very different because the volume fraction and stability of retained austenite vary with the heat treatments. The best low-temperature impact toughness is achieved after heat treating at 873 K (600 °C) for 2 hours due to the formation of a considerable volume fraction of retained austenite with relatively high stability, but the strain hardening capacity and ductility are disappointing because of insufficient TRIP effect. Based on enhancing TRIP effect, the two methods have been suggested. One is to increase the isothermal holding temperature to 893 K (620 °C), and the other one is to prolong the isothermal holding time to 10 hours at 873 K (600 °C). The two methods can significantly increase strain hardening capacity and ductility nearly without harming low-temperature impact toughness. In addition, the stability of retained austenite has been discussed by the quantitative analysis and it has been demonstrated that the stability of retained austenite is related to the chemical composition, size, and morphology. Moreover, the isothermal holding temperature has a great effect on the stability of retained austenite, while the effect of the isothermal holding time is relatively poor.

Three-phase modeling of viscoelastic nanofiber-reinforced matrix

In this paper three-phase fiber-reinforced matrix is analyzed using analytical micromechanical model named simplified unit cell method (SUCM). The system consists of transversely isotropic elastic nanotube and viscoelastic matrix and interphase region. This interphase region comprises considerable volume fraction of the system because of large surface area per unit volume of the nanotubes. However, volume fraction of the interphase in particular short fiber system is considerably small to contribute to the whole properties of it. The presented closed-form solutions are able to predict the effective response of the three-phase fiber-reinforced matrix in any combination of normal and shear loading conditions. To verify the results, creep compliance of Graphite/Epoxy in 10° and 45° and 90° off-axis conditions are compared with existing data. Nanotube/Polycarbonate is also examined to investigate the effect of interphase on viscoelastic behaviors of nanocomposites.

Aerosol physical and chemical properties retrieved from ground-based remote sensing measurements during heavy haze days in Beijing winter

Abstract. With the increase in economic development over the past thirty years, many large cities in eastern and southwestern China are experiencing increased haze events and atmospheric pollution, causing significant impacts on the regional environment and even climate. However, knowledge on the aerosol physical and chemical properties in heavy haze conditions is still insufficient. In this study, two winter heavy haze events in Beijing that occurred in 2011 and 2012 were selected and investigated by using the ground-based remote sensing measurements. We used a CIMEL CE318 sun–sky radiometer to retrieve haze aerosol optical, physical and chemical properties, including aerosol optical depth (AOD), size distribution, complex refractive indices and aerosol fractions identified as black carbon (BC), brown carbon (BrC), mineral dust (DU), ammonium sulfate-like (AS) components and aerosol water content (AW). The retrieval results from a total of five haze days showed that the aerosol loading and properties during the two winter haze events were comparable. Therefore, average heavy haze property parameters were drawn to present a research case for future studies. The average AOD is about 3.0 at 440 nm, and the Ångström exponent is 1.3 from 440 to 870 nm. The fine-mode AOD is 2.8 corresponding to a fine-mode fraction of 0.93. The coarse particles occupied a considerable volume fraction of the bimodal size distribution in winter haze events, with the mean particle radius of 0.21 and 2.9 μm for the fine and coarse modes respectively. The real part of the refractive indices exhibited a relatively flat spectral behavior with an average value of 1.48 from 440 to 1020 nm. The imaginary part showed spectral variation, with the value at 440 nm (about 0.013) higher than the other three wavelengths (about 0.008 at 675 nm). The aerosol composition retrieval results showed that volume fractions of BC, BrC, DU, AS and AW are 1, 2, 49, 15 and 33%, respectively, on average for the investigated haze events. The preliminary uncertainty estimation and comparison of these remote sensing results with in situ BC and PM2.5 measurements are also presented in the paper.

Properties and electrokinetic behavior of non-dilute colloidal suspensions

This paper is a critical review of how the fluid properties (e.g., density, viscosity, conductivity, and permittivity) and behaviors (e.g., electrophoretic motion, electrokinetic aggregation, chaining, and instabilities) depend on colloid volume fraction. The review focuses on electrokinetic flows in aqueous solutions with suspensions on the order of a few percent that are not considered concentrated, yet may exhibit several behaviors distinct from dilute systems such as non-linear dependence on the particle volume fraction and unexpected behavior such as chaining, aggregation, and instabilities. This non-dilute regime is applicable to a variety of emerging applications such as field induced pattern formations in colloidal dispersions, electrophoretic deposition of colloidal films, nanofluid based thermal management, micron resolution particle image velocimetry, and field induced separations in lab-on-a-chip devices. These applications are often treated as dilute when in fact they may contain considerable volume fractions of particles with significant variations in the particle mobility, fluid electrical conductivity and permittivity, as well as the fluid behavior. Original results on electric field induced particle chaining and aggregation as well as fluid instabilities that may develop due to variations in conductivity and permittivity fields are briefly presented.

Intergranular liquation cracking in heat affected zone of a welded nickel based superalloy in as cast condition

The microstructures of the as cast and the heat affected zone (HAZ) of tungsten inert gas welded IN738 superalloy were studied. A different secondary solidification microconstituent was observed in front of some of γ–γ′ eutectic in interdendritic regions of the as cast alloy, which is likely formed by an invariant eutectic type reaction during the terminal stage of the ingot solidification. On welding, the alloy in as cast condition, suffered extensive grain boundary liquation cracking in the HAZ regions while the fusion zone was free of exclusive centerline cracking. Subsolidus liquation reactions of terminal solidification microconstituent, MC type carbides and γ′ precipitate particles present in the preweld alloy in considerable volume fraction, were observed to be major causes of HAZ intergranular liquation and the attendant cracking. Good wetting behaviour of the grain boundary liquid film possibly aided by surface active boron atoms released by the liquation of the terminal solidification reaction product is suggested as an important factor contributing to high susceptibility of the alloy to HAZ cracking in the as cast condition.

Properties of jet engine combustion particles during the PartEmis experiment: Microphysics and Chemistry

The particles emitted from an aircraft engine combustor were investigated in the European project PartEmis. Measured aerosol properties were mass and number concentration, size distribution, mixing state, thermal stability of internally mixed particles, hygroscopicity, and cloud condensation nuclei (CCN) activation potential. The combustor operation conditions corresponded to modern and older engine gas path temperatures at cruise altitude, with fuel sulphur contents (FSC) of 50, 410, and 1270 μg g−1. Operation conditions and FSC showed only a weak influence on the microphysical aerosol properties, except for hygroscopic and CCN properties. Particles of size D ≥ 30 nm were almost entirely internally mixed. Particles of sizes D < 20 nm showed a considerable volume fraction of compounds that volatilise at 390 K (10–15%) and 573 K (4–10%), while respective fractions decreased to <5% for particles of size D ≥ 50 nm.

Modelling the structure and function of extracellular polymeric substances in biofilms with new numerical techniques

The objective of this study is the mathematical description of the structure and function of the extracellular polymeric substances (EPS) in biofilms. The basic assumptions of the EPS biofilm model are: the production of EPS in biofilms is coupled to the growth of micro-organisms the production of EPS is additionally coupled to the substrate conditions the EPS represent a considerable volume fraction of the matrix in biofilms and thus the density of the biofilms is strongly influenced by the EPS sorption of biocides and pollutants in biofilms occurs mainly to EPS the EPS can be used as an energy source during substrate limited phases. The mathematical model has been derived as a system of partial differential equations. The numerical solution of these complex balance equations has been done by a self-adaptive Galerkin-h-p-method. It can be shown, that on the one hand the simulation of substrate conversion and biofilm growth with the EPS-biofilm model yields similar results as the known biofilm models without consideration of the EPS fraction. On the other hand the advantage of the EPS-biofilm model is a better understanding of biofilm structure, which is mainly influenced by the EPS fraction in the biofilm. Furthermore, the sorption of pollutants, such as heavy metals and chlorinated organic substances, can be simulated in more detail.

Reconciliation of the microcrystalline and the continuous random network model for amorphous semiconductors

AbstractWe show by molecular dynamics simulations, that the radial distribution function of an amorphous material does not change significantly by introducing a considerable volume fraction of nanocrystals. The nanocrystals, embedded in a continuous random network, ensure a certain degree of medium range order in the amorphous material. Our simulations, which are on germanium, show that microcrystals smaller than 2 nm can comprise at least 20 % of the volume without significantly changing the radial distribution function from that of pure continuous random network. By increasing the size of the crystals, without altering the crystal to amorphous volume ratio, the radial distribution changes. The molecular dynamics simulations show that the nanocrystals are unchanged at low temperature. At higher temperature the mobility and critical size of the grains increase, transforming the sub-critical crystalline grains into the surrounding continuous random network matrix.

Numerical analysis of the rapid solidification of gas-atomized Al-8 Wt Pct Fe droplets

A numerical analysis of the microstructural evolution of microcellular and cellular α-Al phase in gas-atomized Al-8 wt pct Fe droplets was represented. The two-dimensional (2-D) non-Newtonian heat transfer and the dendritic growth theory in the undercooled melt were combined, assuming a point nucleation on the droplet surface and the macroscopically smooth solid-liquid interface enveloping the cell tips. It reproduced the main characteristic features of the reported microstructures quite well and predicted a considerable volume fraction of thermal dendritic growth region in a droplet smaller than 10 μm if an initial undercooling was larger than 100 K. The volume fractions of the microcellular region, gA, and the sum of the microcellular and cellular region, gα, were predicted as functions of the heat-transfer coefficient, h, and the initial undercooling, ΔT. It was shown that gA and gα, in the typical atomization processes with h = 0.1 to 1.0 W/C.M2K, are dominated by ΔT and h, respectively, but for h larger than 4.0 W/C.M2 K, a fully microcellular structure can be obtained irrespective of the initial undercooling.

Neutron reflectometry from stereotactic isomers of poly(methyl methacrylate) monolayers spread at the air-water interface

Surface pressure-area isotherms on poly(methyl methacrylate) ‘monolayers’ spread at the air-water interface show that the isotactic polymer is in good solvent conditions, whereas the atactic and syndiotactic isomers are in thermodynamic environments that are worse than ‘theta’ conditions. Neutron reflectometry data have been analysed to give monolayer thickness and composition. At low surface concentrations, the layer thickness of the syndiotactic polymer increases to an eventually constant value although the surface pressure and concentration increase still further. For the isotactic polymer, the layer thickness is essentially constant over the range of surface concentrations investigated. Initially, the monolayers contain a considerable volume fraction of air, which decreases as the surface concentration increases. The monolayer thicknesses obtained are considerably larger than recent estimates from ellipsometry measurements, and possible sources for this discrepancy are discussed.

Morphometry of the Subepithelial Circulation in Sheep Airways: Effect of Vascular Congestion

In order to quantitate the subepithelial microvascular volume and its relation to the airway lumen, we conducted a morphometric analysis of the vascular compartment in the wall of the trachea (within a 55-microns depth from the epithelial basement membrane) and of 1.0 and 0.5-mm bronchioles of sheep. The lungs were fixed by bronchial and pulmonary artery perfusion with glutaraldehyde under three experimental conditions: (1) bronchial artery pressure, 100 mm Hg pulmonary artery pressure, 20 mm Hg (control); (2) bronchial artery pressure, 100 mm Hg, pulmonary artery pressure, 40 mm Hg (pulmonary hypertension, PH); (3) bronchial artery pressure, 100 mm Hg, pulmonary artery pressure, 40 mm Hg (pharmacologic vasodilation with sodium nitroprusside, PH + V). Venous pressures were atmospheric. Under control conditions, the microvascular volume fraction comprised 12, 16, and 15% of the subepithelial tissue in the trachea and 1-mm and 0.5-mm bronchioles, respectively. PH increased the microvascular volume fraction in the bronchioles (p less than 0.05), but it had no effect on the microvasculature in the trachea. PH + V approximately doubled the microvascular volume fraction in the trachea and the bronchioles. PH increased the mean wall thickness, and PH and PH + V decreased the airway cross-sectional area in the 1-mm bronchioles. These observations demonstrate that the microvasculature constitutes a considerable volume fraction of the subepithelial airway tissue and that vascular congestion can narrow the bronchiolar lumen.

Fabrication and properties of rapidly solidified powder-based high-temperature application light-alloy composites

Particulate-reinforced composites based on Al-Fe-Ce and SiC were fabricated by conventional powder metallurgy techniques, namely powder mixing, cold compaction and hot extrusion. Static mechanical properties at ambient temperature and at elevated temperature after prolonged exposure to the test temperature were measured and related to process parameters and the volume fraction of the reinforcement. The addition of SiC particles in considerable volume fractions help to retain the static properties at high temperature, even after prolonged exposure. It was also observed that the mechanical strength increases with decreasing temperature and extrusion ratio. Unavoidable non-uniform distribution of SiC particles and the associated porosity were observed to be responsible for wide variations in the properties within the same extrudate. Attempts to reduce this variation are discussed.