Combined Effects Of Porosity Research Articles

Densification and microstructural correlation with thermo-mechanical strength of TiO2-doped (Al1-xCrx)2O3 (x=0.1, 0.3) solid solution ceramics

In this work, TiO2-doped (Al1-xCrx)2O3 (x = 0.1, 0.3) ceramics were prepared in the range of 1600 °C–1700 °C under a slightly reducing atmosphere. The lattice parameter calculations only showed a minor increment with TiO2 doping, implying a meager solid-solubility limit (also detected by EDS semi-quantification). The grain size of (Al1-xCrx)2O3 is directly proportional to the TiO2 amount and sintering temperature. Beyond the TiO2 solid solubility limit, exaggerated grain growth and excessive pore formation were observed at higher sintering temperatures. The highest flexural strengths were observed without TiO2 at a higher sintering temperature and with 1 wt% TiO2 at lower sintering temperatures. However, higher TiO2 inclusion has deleterious effects on flexural strengths, as the failure occurs via a combined effect of porosity and larger grains.

Research on the Performance of Superhydrophobic Cement-Based Materials Based on Composite Hydrophobic Agents.

The utilization of a novel monolithic superhydrophobic cement material effectively prevents water infiltration and enhances the longevity of the material. A method for improving superhydrophobic concrete was investigated with the aim of increasing its strength and reducing its cost by compounding superhydrophobic substances with water repellents. The experimental tests encompassed the assessment of the compressive strength, contact angle, and water absorption of the superhydrophobic cementitious materials. The findings demonstrate that an increase in the dosage of isobutyltriethoxysilane (IBTES) progressively enhances the contact angle of the specimen, but significantly diminishes its compressive strength. The contact angle of SIKS mirrors that of SIS3, with a superior compressive strength that is 68% higher. Moreover, superhydrophobicity directly influences the water absorption of cementitious materials, with a more pronounced superhydrophobic effect leading to a lower water absorption rate. The water absorption of cementitious materials is influenced by the combined effect of porosity and superhydrophobicity. Furthermore, FT-IR tests unveil functional mappings, such as -CH3 which can reduce the surface energy of materials, signifying successful modification with hydrophobic substances.

Combined effects of porosity and degree of saturation on the mechanical properties and deformation behaviour of rocks

To reveal the roles of pores and fissures in the rock-weakening effect of water, this study used porosity to quantitatively characterize pores and fissures in rocks. Based on the results from mechanical tests on rock specimens with different porosities and degrees of saturation, the combined effects of the porosity and water content on the mechanical properties and deformation behaviour of rocks were investigated. The test results indicated that the rock-weakening effect of water was markedly more significant if the pores and fissures in the rock were highly developed. The test data showed that the ratio of saturated specimen strength/dry specimen strength of porous rock can be even lower than 0.1. The least-squares regression method was used to derive the impact of rock porosity on rock weakening due to the effect of water. Based on the results, a practical engineering method for modifying the mechanical parameters of wet rocks with highly developed pores and fissures was proposed. This method can be used to calculate the stress–strain state of rocks more accurately.

Experimental Investigation of the Effect of Groundwater on the Relative Permeability of Coal Bodies around Gas Extraction Boreholes.

Water infiltration in boreholes is a common problem in mine gas pre-extraction, where water infiltration can significantly reduce the efficiency of gas extraction and curtail the life cycle of the borehole. It is important to evaluate the effect of groundwater on the permeability of the coal body around a gas extraction borehole. In order to determine the seepage parameters of the fractured coal body system around the borehole, a water–gas two-phase seepage test was designed to determine the relative seepage parameters of the fractured coal media seepage system. The main conclusion is that the relative permeability of gas can be effectively increased by increasing the negative extraction pressure at the early stage of extraction to accelerate drainage to reduce the water saturation of the coal seam. Under the combined effect of porosity and seepage pressure, the relative permeability of gas and water in the fractured coal rock body shows three stages. The dependence of the total permeability on the effective stress is closely related to the stages in the evolution of the pore structure, and the total effective permeability decreases with the increase in the effective stress. A decrease in porosity can lead to a decrease in permeability and an increase in the non-Darcy factor. Through an in-depth analysis of the damage and permeability pattern of the coal body around the perimeter of the dipping borehole, the efficient and safe extraction of gas from dipping boreholes in water-rich mines is thus ensured.

Exploring the morphology of flax fibres by X-ray microtomography and the related mechanical response by numerical modelling

The external shape and internal lumen of flax fibres are investigated using X-ray microtomography (µ-CT) and finite element (FE) modelling. µ-CT reveals an intricate flax fibre and lumen morphology, with mean porosity contents between 0 and 7.2%. The FE model is based on 3D volumes obtained by X-ray µ-CT and tensile testing in the elastic domain. Numerical results demonstrate the decrease of stiffness as a combined effect of porosity and stress heterogeneity triggered by geometrical considerations. Moreover, stress concentrations induced by both surface roughness and complex lumen shape were observed, highlighting their possible implication in failure mechanisms. However, Young’s moduli are overestimated compared to experimental curves and non-linearities are not considered by the rather strong hypothesis of this model (linear elastic material: no viscosity, plasticity or damage mechanisms taken into account). Future work should include the orientation and reorientation of cellulose microfibrils upon tensile testing, as well as damage mechanisms.

Influence of porosity and permeability of flow distributor on thermal stratification in single media storage tank

A single media single tank system is emerging as a promising technology for thermal energy storage. The incorporation of a porous flow distributor in such a system leads to significant improvement of the thermal stratification in the tank. The performance of the flow distributor depends upon the porous structure of the distributor wall. The influence of the distributor on the thermal stratification is well documented; however, the combined effect of porosity and permeability on the thermocline thickness is not yet explored. The objective of the present study is, therefore, to investigate the interdependent effect of the permeability and porosity of the distributor wall on the thermal stratification in the single media single tank storage system. A numerical analysis is performed to evaluate the establishment and progress of thermocline in the storage tank for a wide range of wall-permeability of the vertically mounted flow distributor. The performance of the flow distributor in minimizing the mixing is analyzed through the velocity and temperature fields, stratification number, MIX number, and span of the logistic cumulative distribution function. Results show that the permeability in the range between 10−9 m2 and 10−8 m2, leads to the best thermal stratification and minimum mixing of energy among the given system configurations. Also, the minimal thermocline thickness is achieved to be ∼13% of the entire tank height which is, to the best of our knowledge, considerably lower than the reported value in literature.

The combined effect of porosity of porous media and longitudinal magnetic field on stability of the modified plane Poiseuille flow

The combined effect of porosity of porous media and longitudinal magnetic field on stability of the modified plane Poiseuille flow

Combined effects of porosity and stress state on the failure behavior of laser powder bed fusion stainless steel 316L

Two primary variables that impact failure behavior of ductile metals are defects and stress state. These factors are especially critical in additively manufactured materials, as components made by additive manufacturing (AM) can have complex shapes that result in the material being subjected to multiaxial stresses under load, and these materials may also contain internal porosity due to AM processing. This study experimentally investigates the effects of both internal pores and stress state on the ductile failure behavior of laser powder bed fusion additively manufactured 316L stainless steel through the introduction of intentional penny-shaped pores of varying size at the center of samples whose geometries result in different stress states. It was found that strain to failure depended strongly on stress triaxiality until a large pore size with a diameter of 1200 µm (4% cross-sectional area of the sample gauge sections), while strain to failure was independent of stress triaxiality, and only a function of pore diameter, with larger pores (9% cross-sectional area or larger).

Model for Predicting the Thermal Conductivity of Concrete

Thermal conductivity of concrete greatly influences the heat transfer of buildings and affected by many factors. This paper presents a prediction model for thermal conductivity of concrete by adopting the theory of Wiener bounds and considering concrete to have four components (water, air, aggregate, and cement mortar). The proposed model considers the combined effects of porosity, water saturation, and the volume fraction of aggregate on the thermal conductivity of concrete by weighting parameters of $${\eta }_{1}$$ , $${\eta }_{2}$$ , $${\eta }_{3}$$ , respectively. By adjusting the weighting parameters of each component, the model can consider the influence of various factors on the thermal conductivity of concrete more comprehensively. Thermal conductivity of each component and expression of weighting parameters are determined by literature and experiments. The proposed model has been verified by the measured thermal conductivity of concrete under different porosities, water content, and volume fractions of aggregate with the prediction accuracy of $$\pm 12\mathrm{\%}$$ . Finally, the regularity of the change in the thermal conductivity of concrete with porosity, water saturation, the volume fraction of aggregate, and temperature is analyzed.

UNSTEADY FLOW OF CASSON LIQUID FILM ON A STRETCHING SHEET WITH RADIATIVE HEAT TRANSFER

Flow of thin uniform Casson liquid film on an unsteady porous stretching sheet is studied both analytically and numerically. Combined effects of porosity, transverse magnetic field, thermal radiation, suction/injection, and thermocapillarity are considered for analysis. Results showed that the film thickness enhances with the Casson parameter, porosity parameter, Hartmann number and injection velocity but the opposite phenomenon is observed for suction velocity, thermocapillary and thermal radiation parameters. The behavior of the temperature field has been discussed with different physical parameters.

Process induced alignment of carbon nanotube decreases longitudinal thermal conductivity of Al2O3 based porous composites

Abstract Alumina (Al2O3) based porous composites, reinforced with zirconia (ZrO2), 3 and 8 mol% Y2O3 stabilized ZrO2 (YSZ) and 4 wt% carbon nanotube (CNT) are processed via spark plasma sintering. The normalized linear shrinkage during sintering process of Al2O3-based composite shows minimum value (19.2–20.4%) for CNT reinforced composites at the temperature between 1650 °C and 575 °C. Further, the combined effect of porosity, phase-content and its crystallite size in sintered Al2O3-based porous composite have elicited lowest thermal conductivity of 1.2 Wm−1K−1 (Al2O3-8YSZ composite) at 900 °C. Despite high thermal conductivity of CNT (∼3000 Wm−1K−1), only a marginal thermal conductivity increase (∼1.4 times) to 7.3–13.4 Wm−1K−1 was observed for CNT reinforced composite along the longitudinal direction at 25 °C. The conventional models overestimated the thermal conductivity of CNT reinforced composites by up to ∼6.7 times, which include the crystallite size, porosity, and interfacial thermal resistance of Al2O3, YSZ and, CNT. But, incorporation of a new process induced CNT-alignment factor, the estimated thermal conductivity (of

Physical modeling of oil charging in tight reservoirs: A case study of Permian Lucaogou Formation in Jimsar Sag, Junggar Basin, NW China

Abstract Modeling experiments of oil charging were conducted to find out patterns and affecting factors of oil migration and seepage in tight reservoirs, and analyze oil migration and accumulation and low limit conditions of tight oil accumulation using core samples from tight reservoir beds of the Permian Lucaogou Formation in the Jimsar Sag of the Junggar Basin. Crude oil charging in tight reservoir beds has two pressure gradient points (start-up pressure gradient and critical pressure gradient, and has two features: low velocity non-Darcy seepage, quasi-linear seepage). During crude oil charging in tight reservoir beds in the Lucaogou Formation, the process of oil saturation increase can be divided into three types: saltation increase, quick increase and stable increase. Samples of quick increase type reached the highest oil saturation, the second place is the stable increase type, and saltation increase type is the last. Oil saturation increase is controlled by the combined effect of porosity, permeability, oil viscosity and displacement pressure gradient. These factors interact and complement one another. By establishing template for oil accumulation in tight reservoir beds, it can be seen that only when pressure gradient breaks through the critical pressure gradient and the oil flow is quasi-linear, can oil saturation reaches the lower limit value (30%) in tight reservoir beds. It is hard for stable tight reservoir beds to become tight firstly and be charged with oil and gas later; while for conventional reservoir beds, after oil and gas charging, the formation compaction, cementation, and secondary mineral outgrowth may be the reasons for the formation of tight oil accumulation with high oil saturation.

The relative contributions of non-enzymatic glycation and cortical porosity on the fracture toughness of aging bone

The risk of fracture increases with age due to the decline of bone mass and bone quality. One of the age-related changes in bone quality occurs through the formation and accumulation of advanced glycation end-products (AGEs) due to non-enzymatic glycation (NEG). However as a number of other changes including increased porosity occur with age and affect bone fragility, the relative contribution of AGEs on the fracture resistance of aging bone is unknown. Using a high-resolution nonlinear finite element model that incorporate cohesive elements and micro-computed tomography-based 3d meshes, we investigated the contribution of AGEs and cortical porosity on the fracture toughness of human bone. The results show that NEG caused a 52% reduction in propagation fracture toughness (R-curve slope). The combined effects of porosity and AGEs resulted in an 88% reduction in propagation toughness. These findings are consistent with previous experimental results. The model captured the age-related changes in the R-curve toughening by incorporating bone quantity and bone quality changes, and these simulations demonstrate the ability of the cohesive models to account for the irreversible dynamic crack growth processes affected by the changes in post-yield material behavior. By decoupling the matrix-level effects due to NEG and intracortical porosity, we are able to directly determine the effects of NEG on fracture toughness. The outcome of this study suggests that it may be important to include the age-related changes in the material level properties by using finite element analysis towards the prediction of fracture risk.

Effect of pressure, temperature, and oil-saturation on the thermal conductivity of sandstone up to 250 MPa and 520 K

Effective thermal conductivity (ETC) of oil-saturated sandstone (porosity 13%) have been measured over a temperature range from (288 to 520) K and at pressures up to 250 MPa with a steady-state parallel-plate apparatus. The expanded uncertainty of thermal conductivity, pressure, and temperature measurements at the 95% confidence level with a coverage factor of k = 2 were estimated to be 2%, 0.05%, and 30 mK, respectively. The estimated uncertainty in ETC measurement does not include the uncertainty due to contact thermal resistance and radiative conductivity. A rapid increase of ETC was found for oil-saturated sandstone at low pressures between (0.1 and 100) MPa along various isotherms. At high pressures ( P > 100 MPa) a weak linear dependence of the ETC with pressure was observed. The pressure effect is negligible small after the first 100 MPa where bridging of microcracks or improvement of grain contacts take place. The temperature, ∂ ln λ / ∂ T P , and pressure, ∂ ln λ / ∂ P T , coefficients for oil-saturated sandstone were calculated by using the measured ETC. We interpreted measured ETC data for oil-saturated sandstone using various theoretical models in order to check their accuracy, predictive capability, and applicability. We demonstrated that the combined effect of porosity, temperature, pressure, and fluid saturation can be predicted accurately using a Zimmerman's model. The effect of saturating fluids, structure (size, shape, and distribution of the pores), porosity, and mineralogical composition on temperature and pressure dependences of the ETC of oil-saturated sandstone was discussed.

The combined effect of porosity and reactivity of the carbon preforms on the properties of SiC produced by reactive infiltration with liquid Si

This study is focused on the effect of the porosity and chemical reactivity with silicon of the carbon preforms on the properties of SiC pieces produced by reactive infiltration. Petroleum residues were selected as carbon precursor because of their unique combination of properties. On the one hand, semicoke powders with optimum self-sinterability can be obtained from them to develop a wide range of porous carbon preforms without addition of binder to carry out the porosity study. On the other hand, reactivity of the carbon material with silicon can be modified by employing semicokes with different mesophase microstructure obtained from petroleum residues with different chemical composition. SiC yield was strongly affected by the degree of anisotropy of the carbon material, the most ordered carbon being more reactive. SiC pieces made from the optimum carbon preforms (made up by combining the most graphitic carbon and 40% of open porosity) achieved bending strength values of around 260 MPa. Chemical reactivity of carbon substrates was also modified by graphitization treatment. An improvement in the mechanical properties of SiC pieces up to 66% was achieved due to the structural modification caused by graphitization of the carbon preforms. Bending strengths twice the value of commercially available ones were achieved.

Dependence of Mechanical Strength of Brittle Polycrystalline Specimens on Porosity and Grain Size

An empirical equation form, approximating the apparent dependence of the strength of brittle polycrystalline specimens on the combined effect of porosity and grain size, has been developed from concepts and data in the literature. The form is shown to be applicable to data for thoria and chromium carbide specimens.