Porosity Fraction Research Articles

Evolution of Mineral-Accessible Surface Area Induced by Geochemical Reactions

Mineral dissolution and precipitation reactions occur in a wide range of porous media systems, driven by deviations from an equilibrium between solid and fluid phases. Reactions occur at mineral surfaces in contact with reactive fluids or accessible mineral surface areas. These mineral surface areas can be determined using a multiscale imaging approach and have been shown to improve the simulation of mineral reaction rates in porous media compared to other estimates of reactive surface area. As reactions progress, mineral surface area evolves, and reactive transport simulations often use a simplified model assuming spherical grains to estimate mineral surface area evolution. This, however, does not depict the evolution of reactive surfaces in porous media systems with varying mineral accessibility. This work aims to quantitatively assess the evolution of accessible mineral surface area in porous media for a multimineralic system undergoing mineral dissolution reactions induced by acid exposure. Before and after the reaction, accessible mineral surface areas are determined from 2D scanning electron microscopy, and 3D X-ray computed tomography imaging of a sandstone sample. The quantified evolution of accessible surface area is compared to the calculated mineral surface area evolution using current approaches. Results show an overall increase in total surface area due to the reaction; however, individual mineral surface areas may increase or decrease. Variation is observed in mineral surface area values measured from imaging and equations used in models. The evolution of mineral surface area is largely impacted by the total surface area as well as the pore connectivity rather than porosity and volume fraction evolution.

Bending-bending coupled static analysis of functionally graded and porous pretwisted cantilever beams using initial values method

In this study, the bending-bending coupled static behavior of functionally graded and porous pretwisted cantilever Timoshenko beams is reported. Symmetric power-law distribution is employed as the material profile and it is assumed that porosity can disperse over the cross-section in two forms namely, even and uneven distributions. Two different yet equivalent forms of governing equations are obtained by formulating the problem in the fixed and curvilinear coordinate systems, respectively. The initial values method is adopted as the solution methodology. While the fundamental matrix is computed numerically by using the multiplicative integral of Volterra to obtain the solution in the fixed coordinate formulation, the matrix exponential which allows for obtaining exact expressions is utilized in the curvilinear coordinate formulation. Exact analytical deflection expressions are presented for space-fixed vertical tip force and body-fixed uniform distributed force cases. It is shown that both formulation approaches yield consistent results with each other and those obtained from the finite element analyses. In addition, several parametric studies that investigate the effects of the volume fraction index, porosity coefficient, and porosity distribution on the tip deflections are presented.

High density Fe-based soft magnetic composites with nice magnetic properties prepared by warm compaction

The influences of compacting temperature (Tc), molding pressure (Pm), contents of lubricant (Cl) and binder (Cb) on the compacted density (ρc) and its comprehensive soft magnetic properties for the FeSiCr soft magnetic composites (SMCs) fabricated by warm compaction were systematically studied. Appropriate increase of Tc is beneficial to improve the surface lubrication effect of magnetic powders during the forming process of SMCs, thus giving rise to the increase of ρc and the decrease of porosity fraction for the SMCs. Under this situation, the resistance of domain rotation and domain wall displacement in the SMCs during magnetization process is reduced, which is finally in favor of the improvement of SMCs’s soft magnetic properties. The results of loss separation show that the Ph value plays a dominant role in the variation trend of Pcv value for the FeSiCr-SMCs in the test frequency range of 20–200 KHz, wherein the ratio of Ph/Pcv is large than 81 %. Under the optimized process parameters of Tc= 110 ℃, Pm= 600 MPa, Cl= 1.5 wt. % and Cb = 2.5 wt. %, the ρc of FeSiCr-SMCs increases by 8.14 % to 6.38 kg/m3, and the SMCs exhibit better comprehensive soft magnetic properties compared with those at Tc = 25 ℃. Hereinto, μe increases by 19.89 % to 45.8 @ 100 kHz, Pcv decreases by 26.11 % to 495.8 kW/m3@f= 100 kHz, Bm= 50mT, and μe % reached 85.5 % at H = 8000 A/m. These results indicated that the warm compaction process is one of the effective ways to further promote Fe-based SMCs to meet the development requirements of high-frequency, miniaturization and high-power of electronic equipment.

The effect of size and shape of pores on the prediction model of compressive strength of foamed concrete

The Balshin’s model is the most well-known of the models used to predict the compressive strength of aerated concrete. Among the pore characteristics such as the amount of porosity, the size of the pores, and their shape, Only the amount of porosity is placed as a specific parameter in the Balshin’s model. The impact of the other two characteristics, on the other hand, is included in the power value of the Balshin’s equation. Compressive strength tests and identifying the characteristics of air voids using microscopic imaging were performed on the mixtures produced in this study, which had weight ratios of sand to the cement of 1, 1.5, and 2, and the percentage of foam volumes of 0, 15, 25 and 35. In this study, a review of some of the factors influencing the change in the pore characteristics was performed, including the porosity of the foamed mixture and the size of sand used, in addition to the effect of the pore characteristics such as size and shape on the compressive strength of the foamed mixture. This study aims to conduct a comparative analysis of the models introduced in previous research to determine the effect of the pore characteristics of semi-structural and structural foamed mixtures (with sand) caused by mixture porosity and the sand size on the Balshin’s model. Among the types of relationships presented for the Balshin’s model, the relationship based on the paste fraction porosity was used. According to the findings of this study, foam porosity is the most important factor influencing pore size change, followed by sand size. The increase in the size of the pores and their non-sphericality decreased the relative compressive strength and, as a consequence, increased the power of the Balshin’s model because the maximum level of stress concentration was created adjacent to the middle diameter of the pores at the period of concrete rupture.

The Relationship Between Fiber Bundle Size and Mechanical Performance of Additively Manufactured Continuous Carbon Fiber Reinforced Thermoplastic Composites.

Additively manufactured continuous fiber-reinforced thermoplastic (CFRTP) composites are still in the early stages of reaching competitive mechanical properties compared with conventional composites. The main reason for this is that their mechanical properties are limited due to weak interlayer strength, porosity, and low fiber fraction. Therefore, the effects of many parameters, such as layer thickness, temperature, printing speed, and fiber fraction, have been extensively studied to improve mechanical properties. With a different perspective on these parameters, this study aimed to investigate the effect of fiber bundle size on the mechanical properties of CFRTP composites. For this purpose, 3K and 6K fiber bundle filaments with the same fiber volume fractions (∼41%) were produced utilizing a polymer impregnation setup. CFRTP samples were printed using fused deposition modeling with polylactic acid as the matrix. The mechanical properties were investigated via three-point bending, interlaminar shear strength (ILSS), and tensile tests. The results showed that fiber bundle size does not particularly influence tensile strength but dominates flexural and ILSS performance. Although increased flexural strength and modulus were observed, the bundle size effect was much more dominant in ILSS tests, and 6K bundle size samples with the same fiber fraction showed much higher strength.

Molecular-Dynamics Analysis of the Mechanical Behavior of Plasma-Facing Tungsten.

We report a systematic computational analysis of the mechanical behavior of plasma-facing component (PFC) tungsten focusing on the impact of void and helium (He) bubble defects on the mechanical response beyond the elastic regime. Specifically, we explore the effects of porosity and He atomic fraction on the mechanical properties and structural response of PFC tungsten, at varying temperature and bubble size. We find that the Young modulus of defective tungsten undergoes substantial softening that follows an exponential scaling relation as a function of matrix porosity and He atomic content. Beyond the elastic regime, our high strain rate simulations reveal that the presence of nanoscale spherical defects (empty voids and He bubbles) reduces the yield strength of tungsten in a monotonically decreasing fashion, obeying an exponential scaling relation as a function of tungsten matrix porosity and He concentration. Our detailed analysis of the structural response of PFC tungsten near the yield point reveals that yielding is initiated by emission of dislocation loops from bubble/matrix interfaces, mainly 1/2⟨111⟩ shear loops, followed by gliding and growth of these loops and reactions to form ⟨100⟩ dislocations. Furthermore, dislocation gliding on the ⟨111⟩{211} twin systems nucleates 1/6⟨111⟩ twin regions in the tungsten matrix. These dynamical processes reduce the stress in the matrix substantially. Subsequent dislocation interactions and depletion of the twin phases via nucleation and propagation of detwinning partials lead the tungsten matrix to a next deformation stage characterized by stress increase during applied straining. Our structural analysis reveals that the depletion of twin boundaries (areal defects) is strongly impacted by the density of He bubbles at higher porosities. After the initial stress relief upon yielding, increase in the dislocation density in conjunction with decrease in the areal defect density facilitates the initiation of dislocation-driven deformation mechanisms in the PFC crystal.

Percolation through voids around toroidal inclusions.

In the case of media comprised of impermeable particles, fluid flows through voids around impenetrable grains. For sufficiently low concentrations of the latter, spaces around grains join to allow transport on macroscopic scales, whereas greater impenetrable inclusion densities disrupt void networks and block macroscopic fluid flow. A critical grain concentration ρ_{c} marks the percolation transition or phase boundary separating these two regimes. With a dynamical infiltration technique in which virtual tracer particles explore void spaces, we calculate critical grain concentrations for randomly placed interpenetrating impermeable toroidal inclusions; the latter consist of surfaces of revolution with circular and square cross sections. In this manner, we study continuum percolation transitions involving nonconvex grains. As the radius of revolution increases relative to the length scale of the torus cross section, the tori develop a central hole, a topological transition accompanied by a cusp in the critical porosity fraction for percolation. With a further increase in the radius of revolution, as constituent grains become more ringlike in appearance, we find that the critical porosity fraction converges to that of high-aspect-ratio cylindrical counterparts only for randomly oriented grains.

Parameters Optimization and Repeatability Study on Low-Weldable Nickel-Based Superalloy René 80 Processed via Laser Powder–Bed Fusion (L-PBF)

This work aims to investigate the processability of René 80 via laser powder–bed fusion (L-PBF). René 80 is a poorly weldable Ni-superalloy, currently processed via investment casting to fabricate turbine blades working at an operating temperature of about 850 °C. The L-PBF parameters optimization aims to increase part integrity and enhance processing repeatability. This part was tackled by creating a complete design of experiments (DOE) in which laser power, scan speed and hatching distance were varied accordingly. Optimizing the abovementioned parameters minimized the crack density and pore area fraction. Hence, five parameter sets leading to a crack density lower than 100 µm/mm2 and a pore fraction between 0.045% and 0.085% were selected. Furthermore, the intra-print repeatability was studied by producing three specimens’ repetitions for each optimal set of parameters in the same build. The porosity value obtained was constant among repetitions, and the crack density (around 75 µm/mm2) had a slight standard deviation. The third step of the research assessed the inter-prints repeatability by producing a replica of the five selected parameter sets in a different build and by comparing the results with those studied previously. According to this latter study, the porosity fraction (ca. 0.06%) was constant in intra- and inter-print conditions. Conversely, crack density was lower than 100 µm/mm2 only in three sets of parameters, regardless of the intra- or inter-build cross-check. Finally, the best parameter set was chosen, emphasizing the average flaw fraction (least possible value) and repeatability. Once the optimal densification of the samples was achieved, the alloy’s microstructural features were also investigated.

Modelling of hydrogen diffusion in a steel containing micro-porosity. Application to the permeation experiment

Two numerical models based on non-equilibrium and local equilibrium approaches respectively were developed to simulate hydrogen transport in porous metals, taking account of gaseous hydrogen trapping inside the micro-porosities. They were applied to the case of hydrogen permeation in a cast steel at room temperature. Numerical simulations revealed that the two models are equivalent under certain conditions. A parametric analysis was performed to explore the effect of external hydrogen fugacity, hydrogen solubility and porosity fraction on the hydrogen diffusion behavior. A comparison between experimental permeation data and the numerical results showed reasonable agreement considering no input parameter was adjusted.

Scaling analysis for rapid estimation of lack of fusion porosity in laser powder bed fusion

Lack-of-fusion porosity due to insufficient melting of the adjacent tracks and successive layers is a persistent problem in laser powder bed fusion (LPBF). A novel functional relation is proposed here following dimensional analysis for rapid estimation of the lack-of-fusion porosity fraction as a function of important process variables and alloy properties. The estimated values of the porosity fractions are found to be in fair agreement with the corresponding independent experimentally measured results for LPBF of five commonly used alloys for a wide range of process conditions. The proposed functional relation is used further to construct a set of process maps that can aid in the selection of important LPBF conditions to avoid lack-of-fusion porosity on the shop floor without doing any calculations.

Numerical Modeling Based on Finite Element Analysis of 3D-Printed Wood-Polylactic Acid Composites: A Comparison with Experimental Data

Wood-polymer composites are increasingly produced through fused deposition modeling (FDM)—an additive manufacturing technique. The versatility of this technology has attracted several industries to print complex shapes and structures. This underscores the importance of studying the mechanical properties of the FDM parts, specifically, their elastic properties. A numerical homogenization methodology is introduced in the present study, focusing on the fundamental aspect of the elastic properties. Investigations were carried out on the influence of various parameters like wood volume fraction, aspect ratio, and internal porosity. The numerical results were validated using analytical models and experimental data. The comparison showed a satisfactory agreement with experimental data, where the relative error did not exceed 10%, leading to a strong conclusion about the validity and effectiveness of the proposed approach.

Vplyv Sr, Zr a Mo na vybrané vlastnosti AlSi5Cu2Mg zliatiny

Hypoeutectic AlSi5Cu2Mg alloy is a relatively new alloy that finds application in the production of high stress cylinder head castings. This work focuses on the investigation of the solubility of the additive elements Sr, Zr, and Mo in AlSi5Cu2Mg alloy. The main objective of the work was to characterize the influence of the additive elements on selected properties of the experimental alloy AlSi5Cu2Mg with respect to the melting method of the additive elements. The additive elements Sr, Zr, and Mo were introduced into the melt in the form of AlSr10, AlZr20, and AlMo10 master alloys were melted in 2 ways in an electric resistance furnace and an electric induction furnace. Depending on the melting method, the experimental alloys were designated Sr-Z, Zr-Z, Mo-Z (electric resistance furnace), and Sr-I, Zr-I, and Mo-I (electric induction furnace). The results showed that the presence of Sr, Zr, and Mo in the AlSi5Cu2Mg alloy led to a negative increase in the area fraction of porosity and a decrease in the physical properties, regardless of the melting method of the master alloys. Based on the summarized results, it was shown that the experimental alloys Sr-I, and Sr-Z did not show a significant increase in mechanical properties. A negative effect on the selected mechanical properties was noted by the experimental alloy Zr-Z. The most favourable combination of mechanical properties was obtained by the experimental alloys Mo-I and Zr-I.

Manufacturing of WC-17Co 3D-objects by Laser Powder Bed Fusion followed by heat-treatment

Conventional tungsten carbide (WC) cermet parts containing a cobalt matrix phase are generally produced via powder sintering. In this study it is shown that cermet parts can also be produced by laser powder bed fusion from WC-17Co powder precursor. Optimal process parameters were found for manufacturing without preheated building plate. Micro-structural analysis revealed noteworthy porosity fraction (1.41%) as well as the presence of small-scale cracks in the as-built specimens. It is further shown that most of these defects can be eliminated by heat treatment at ambient pressure or by hot isostatic pressing. Heat treatment also led to the dissolution of the fragile W2C phase. Hardness test results indicate that the performance of the AM parts was comparable to that of a reference produced via powder sintering. The work is a successful demonstration of manufacturing of cermet parts using laser powder bed fusion.

Halloysite-Decorated Mechanically Robust Polyurethane Nanocomposite Foams for Acoustic Relevance

Noise pollution affects human health and the environment. In this study, halloysite nanoclay (HNC) was employed as a bio-nanofiller with different ratios (1–5 wt %) to improve the thermal, mechanical, and sound absorption capabilities of the flexible polyurethane (FPU) foam. FPU/HNC composites were characterized using X-ray diffraction, Fourier transform infrared, and field emission scanning electron microscopy techniques. In addition, porosity, apparent density, and sol fraction for FPU/HNC composites were investigated. Compared with the unfilled FPU foam, the results of the FPU/HNC 1% sample showed that the density achieved a maximum value of 38.17 Kg/m3, while the porosity was reduced to 83.48%. Moreover, the sol fraction reached the highest value of 13.4% for the FPU/HNC 5% sample. Furthermore, thermogravimetric analysis revealed that adding 1 wt % HNC improved thermal stability than the unfilled FPU. Nevertheless, the DSC measurement proved that HNC increased the glass transition temperature (Tg) for the composites’ soft segments. Intriguingly, the mechanical measurements exposed that the compressive and tensile strength of the FPU/HNC 1% sample was enhanced to 158.93 and 154.45%; at the same time, the elongation at break dropped to 124.04%. Nevertheless, the sound absorption measurements (20 mm thickness) showed a slight shift to the mid-frequency range (315–1600 Hz) for FPU/HNC composites than the unfilled FPU.

Effect of high temperature on mechanical properties and porosity of carbon fiber/epoxy composites

In this study, the mechanical behavior and porosity of a T700/epoxy composite material under high temperature conditions were investigated. The 0°/90° compression, tensile, interlaminar, and in-plane shear experiments of composite samples were performed at temperatures from 23°C to 170°C. The true strain–stress curves of composite samples were obtained. The cross section and fracture regions of the tested samples were analyzed by Scanning Electron Microscopy and X-ray tomography to understand the microstructure property relationships. It was observed that the mechanical performance of carbon fiber/epoxy composites generally decreased with increasing temperature. By comparing the fracture morphology, it was found that the fracture mechanism of the composites changed from interfacial debonding to matrix failure with increasing temperature. Three-dimensional visualization of porosities after mechanical experiments under high temperature conditions was reconstituted from X-ray tomography scan images. The results showed that the porosity fraction of the tested samples under high temperature conditions was generally higher than that under lower temperature conditions. Moreover, for the 90° tensile test, the diameter of the pores was mainly located at 4–12 μm and was almost constant along different distances to the failure edge. Meanwhile, compared with the tensile test, larger size of pores in samples of 90° compression tests were observed.

Reservoir Characteristics of the Lower Miocene Carbonate Formations in Kor Mor Gasfield, Kirkuk Area, NE Iraq

This paper presents the evaluations of the reservoir characterization of the Lower Miocene Euphrates, and Jeribe carbonate formations that have been selected for this study in Kor Mor Gasfield in Northeastern Iraq. The Euphrates ranged in thickness between 30 and 65, and Jeribe 30 and 50m in this field, and they are overlain by a thick evaporate cap rock of the Fatha Formation. The two formations are separated by the thin evaporate rock unit of the Dhiban Formation
 The full set of log data for the well Km-9 was used in addition to some general data derived from other eight wells (Km-1 to Km-8). The log data have been used in evaluating the reservoir properties of the two rock units. The detected lithologies from the available mud log and well reports showed that the two formations mostly dolostone and dolomitic limestone were dominated. From the log data, different types of reservoir properties (clay content, clay types, porosity, and fracture index,) have been estimated. The average porosity of the Euphrates reservoir is around of 0.15, and the Jeribe 0.10, the secondary porosity makes a significant fraction of porosity in both units.

How Porosity Affects the Performance of Piezoelectric Energy Harvesters and Sensors

AbstractPorosity has been experimentally employed to enhance the power output of piezoelectric energy harvesters. However, porosity lowers the breakdown voltage of the piezoelectric layer and hampers the pre‐poling of the piezoelectric, which is needed to achieve enhanced performance. Furthermore, the effect of fractional porosity and pore size on the poling conditions and the enhanced power output of the comprising piezoelectric harvesters is not yet known. Here, through finite‐element method simulations, it is shown that the enhanced performance of the porous piezoelectric harvesters is independent of the size and distribution of the pores and only depends on the fractional porosity. Moreover, it is shown that the presence of pores yields the emergence of local stress hot spots that are mainly responsible for improved performance. Moreover, it is suggested that the breakdown issue of the porous piezoelectric layers can be mitigated by poling the structures in a vacuum using electric fields below the threshold field for electron field emission from the piezoelectric layer.

Investigation of microstructures, defects, and mechanical properties of titanium-zirconium-molybdenum alloy manufactured by wire arc additive manufacturing

Titanium‑zirconium‑molybdenum (TZM), one of the refractory alloys, has extraordinary physicochemical properties, making it ideal for usage in extreme environmental applications (e.g., high-temperature and nuclear). Due to the scalability and near-net shape fabrication, metal additive manufacturing processes have several advantages, leading it to be the possible solution for the fabrication of refractory alloy structures. Wire arc additive manufacturing (WAAM) has several advantages, including high deposition rate, energy efficiency, and cost-effective manufacturing of large components. In this study, we comprehensively investigated the relationships among process, microstructures, mechanical properties, and defects of TZM thin-walls manufactured by WAAM using four heat input conditions: 180A, 200A, 220A, and 240A. The microstructures were investigated using multi-scale material characterization techniques. Columnar grains were generated along the build direction, and carbide precipitates were found uniformly distributed in the Mo matrix. Multi-scale pores and cracks were present in the microstructures. The average microhardness values for the deposits ranged from 188.5 to 193.5 hardness scales of Vickers. The highest yield strength, 195 MPa, was found in the 200A heat input condition. The primary fracture mode was identified as a brittle transgranular. The area fraction of porosity was calculated >1% in each condition, with the largest being 2.04% in the 240A deposit.

Solidification behavior and porosity in electron-beam powder bed fusion of Co–Cr–Mo alloys: Effect of carbon concentrations

An increased carbon content strengthens Co–Cr–Mo alloys for use in a broad range of industrial applications. In this study, we investigated the influence of the carbon content (0.04–2.5 mass%) on the porosity and microstructure of Co–27Cr–6Mo (mass%) alloys during atomization and electron-beam powder bed fusion (EB-PBF). Quantitative X-ray computed tomography clarified that the volume fraction of pores in the raw powders monotonically increased with the carbon content, as a potential effect of the significant reduction in the liquidus temperature. In contrast, the porosity evolution in the investigated alloys during EB-PBF under identical building conditions suggested an influence of carbon concentration that was distinct from that in the powder. These alloys exhibited negligible porosity fraction for 0.04 and 0.22 mass% and a maximum volume fraction (∼0.3 vol.%) at 2.0 mass%, followed by a remarkable reduction caused by further carbon addition. The porosity of the as-built alloys could be correlated to the solidification behavior varying with carbon concentration. The smoother and more flat solidification front during the cellular (0.04 and 0.22 mass%) and eutectic (2.5 mass%) solidification could effectively eliminate the gas bubbles from the melt pool, whereas the complicated morphology at the solid–liquid interfaces during the dendritic growth (1.5 and 2.0 mass%) hindered the pore elimination in the melt pool. Adding carbon significantly increased the Rockwell hardness of the as-built specimens, reaching a significantly high value of HRC59 at 2.5 mass% of carbon, primarily due to the formation of hard carbide precipitates. The obtained findings could be beneficial to reduce entrapped gas pores thereby contributing to the development of highly durable metal components.

Thermal Flow for Radiative Ternary Hybrid Nanofluid over Nonlinear Stretching Sheet Subject to Darcy–Forchheimer Phenomenon

This study examines the bidimensional nonlinear convective flow of ternary hybrid nanofluid upon a nonlinear stretching sheet. Three types of nanoparticles, namely Cu , TiO 2 , Al 2 O 3 , are suspended in the base fluid taken as water with a new composition Cu + TiO 2 + Al 2 O 3 / H 2 O which is termed as ternary hybrid nanofluid. To stabilize the flow and thermal properties of the new composition, the Brownian as well as thermophoresis properties are incorporated into energy and mass equations. The nonlinear thermal radiations and heat absorption/generation terms are included in the energy equation. The effects of the Darcy–Forchheimer phenomenon are also induced in the momentum equation. The set of model equations has shifted to dimension-free form by employing suitable variables. It has concluded in this study that flow characteristics have been declined with augmenting values of volumetric fractions of solid nanoparticles, porosity, and inertia factors and have upsurge with higher values of thermal and nonlinear thermal Grashof numbers. Thermal characteristics have been observed to be augmented with growth in radiation, Brownian motion, thermophoresis, heat generation/absorption, temperature ratio factors, and volumetric fraction of solid nanoparticles. These effects are more significant for ternary hybrid nanoparticles. Concentration profiles have been declined with higher values of Brownian motion factor, Lewis number, and upsurge with growth in thermophoresis factor. It has also been deduced in this investigation that the thermal flow rate is higher for trihybrid nanofluid than hybrid or traditional nanofluids, and a percentage growth in Nusselt number has been shown through statistical chart in support of this work. Current results have been compared with established results and found a fine agreement amongst all results.