Porosity Shape Research Articles

Effect of Porosity Shape, Size and Distribution on Stress Intensity Factors in Spot Welded Joints: A Finite Element Study

Effect of Porosity Shape, Size and Distribution on Stress Intensity Factors in Spot Welded Joints: A Finite Element Study

Hydrodynamic Stability Analysis for MHD Casson Fluid Flow through a Restricted Channel

Flow instability is a major challenge experienced in medical, engineering and industrial settings globally. For instance, flow instability linked with irregular cardiac output of the heart leads to organ malfunctioning in the medical field, it also encourages mechanical vibrations in the case of fluctuating flow rate, and several other applications. In this study, linear stability analysis is conducted to monitor the behavior of a small disturbance that is imposed on hydromagnetic Casson fluid that flows steadily through a saturated porous medium. A new variant of the Orr-Sommerfield equation is obtained and solved numerically by using spectral point collocation weighted residual approach with eigenfunction expansion of the Chebyshev polynomial as the admissible trial function. Based on the QZ algorithm, numerical results are obtained for wave and Reynold’s numbers, wave velocity as functions of Magnetic field intensity and porosity shape parameters. Results are validated against previously released data. The biophysics of the heart, particularly in cardiac rhythm analysis, as well as several other medicinal and technical applications, is among the areas where the current work has applicability.

Fluorinated covalent-organic polymers as stationary phase for analysis of organic fluorides by open-tubular capillary electrochromatography.

Fluorinated porous materials, which can provide specific fluorine-fluorine interaction, hold great promise for fluoride analysis. Here, a novel fluorinated covalent-organic polymer was prepared by using 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,3,5,6-tetrafluorotelephtal aldehyde as the precursors and introduced as stationary phase for open-tubular capillary electrochromatography. The as-synthesized fluorinated covalent-organic polymer and the modified capillary column were characterized by infrared spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectrometry. Based on strong hydrophobic interaction and fluorine-fluorine interaction provided by fluorinated covalent-organic polymer coating layer, the modified column showed powerful separation selectivity toward hydrophobic compounds, organic fluorides, and fluorinated pesticides. Additionally, the fluorinated covalent-organic polymer with good porosity and regular shape was uniformly and tightly coated on the capillary inner wall. The obtained highest column efficiency could reach up to 1.2 × 105 plates⋅m-1 for fluorophenol. The loading capacity of the modified column can reach 141pmol for trifluorotoluene. Besides, the relative standard deviations of retention times for intraday run (n=5), interday run (n=3), and between columns (n=3) were all less than 2.55%. Significantly, this novel fluorinated material-based stationary phase shows great application potential in fluorides analysis.

Investigation of the Shape and Detectability of Pores with X-ray Computed Tomography

Component porosity is a quality attribute in additive manufacturing (AM). One possibility for the non-destructive three-dimensional determination of porosity or pore shape is X-ray computed tomography (CT), which enables an investigation of the influence of AM process parameters on the appearance and characteristics of the pores. Since there is no porosity standard for CT, a traceable determination of the measurement uncertainty is not possible. Using a digital twin of the CT system, an estimation of the CT measurement uncertainty is in principle possible. In this contribution, experimental CT analyses of powder bed fusion samples made of Ti64 and PA12 are compared with CT simulations. The results show a size-dependent influence on the shape and detectability of the pores. Using the CT model, a simulated shape- and material-dependent probability of detection (POD) is calculated.

Development of Three-Dimensional (3D) Biodegradable Polyglycolic Acid Fiber (PGA) Preforms for Scaffold Applications: Experimental Patterning and Fiber Volume Fraction-Porosity Modeling Study.

Three-dimensional (3D) biodegradable polyglycolic acid fiber (PGA) preforms were developed as temporary scaffolds for three-dimensional tissue regeneration applications. Three-dimensional biodegradable polyglycolic acid fiber (PGA) preforms including various degrees of interlaced structures called 3D plain, semi-interlaced, and orthogonal woven preforms were designed. Analytical relations and finite element model-based software (TexGen) on fiber volume fraction and porosity fraction were proposed to predict scaffolds' stiffness and strength properties considering micromechanics relations. It was revealed that yarn-to-yarn space, density, and angles of all 3D PGA fiber preforms were heterogeneous and demonstrated direction-dependent features (anisotropy). Total fiber volume fractions (Vfp) and porosity fraction (Vtpr) predicted by analytic and numerical modelling of all 3D scaffolds showed some deviations compared to the measured values. This was because yarn cross-sections in the scaffolds were changed from ideal circular yarn (fiber TOW) geometry to high-order ellipse (lenticular) due to inter-fiber pressure generated under a tensile-based macrostress environment during preform formation. Z-yarn modulus (Ez-yarn) and strength (σz-yarn) were probably critical values due to strong stiffness and strength in the through-the-thickness direction where hydrogel modulus and strengths were negligibly small. Morphology of the scaffold showed that PGA fiber sets in the preform were locally distorted, and they appeared as inconsistent and inhomogeneous continuous fiber forms. Additionally, various porosity shapes in the preform based on the virtual model featured complex shapes from nearly trapezoidal beams to partial or concave rectangular beams and ellipsoid rectangular cylinders. It was concluded that 3D polyglycolic acid fiber preforms could be a temporary supportive substrate for 3D tissue regeneration because cells in the scaffold's thickness can grow via through-the-thickness fiber (z-yarn), including various possible mechanobiology mechanisms.

Bubble collapse near porous plates

The collapse of a gas or vapour bubble near a non-porous boundary is directed at the boundary due to the asymmetry induced by the nearby boundary. High surface pressure and shear stress from this collapse can damage, or clean, the surface. A porous boundary, such as a filter, would act similarly to a non-porous boundary but with reduced asymmetry and thus reduced effect. Prior research has measured the cleaning effect of bubbles on filters using ultrasonic cleaning, but it is not known how the bubble dynamics are fundamentally affected by the porosity of the surface. We address this question experimentally by investigating how the standoff distance, porosity, pore size and pore shape affect two collapse properties: bubble displacement and bubble rebound size. We show that these properties depend primarily on the standoff distance and porosity of the boundary and extend a previously developed numerical model that approximates this behaviour. Using the numerical model in combination with experimental data, we show that bubble displacement and bubble rebound size each collapse onto respective single curves.

Toward accurate prediction of partial-penetration laser weld performance informed by three-dimensional characterization – Part I: High fidelity interrogation

The mechanical response of laser welds in complex load states can be highly variable, underlying the need for models that can accurately predict mechanical behavior to ensure component performance. In Part I of this work, a series of partial penetration welds of 304L stainless steel have been characterized in three dimensions using micro-computed tomography (μCT). The effect of segmentation approaches for handling raw three-dimensional data has been studied in detail. Such characterization enables for comprehensive analysis of the physical distribution and shape of porosity within the weld as well as details on the geometry of the joint, which are used in conjunction with mechanical testing to understand the impact of these factors on weld performance. Joint geometry, in particular the prescribed gap between the plates, has a large impact on the tensile response of weldments, which can be understood to primarily depend on the local load state that develops around the joint. Using high-fidelity three-dimensional data, the mechanical response of individual weldments, including the peak load and displacement to failure, can be accurately predicted using finite element simulations. The details of the modelling approach, and its sensitivity to various idealizations, are the focus of Part II of this work.

Structural Mechanical Properties of 3D Printing Biomimetic Bone Replacement Materials

One of the primary challenges in developing bone substitutes is to create scaffolds with mechanical properties that closely mimic those of regenerated tissue. Scaffolds that mimic the structure of natural cancellous bone are believed to have better environmental adaptability. In this study, we used the porosity and thickness of pig cancellous bone as biomimetic design parameters, and porosity and structural shape as differential indicators, to design a biomimetic bone beam scaffold. The mechanical properties of the designed bone beam model were tested using the finite element method (FEM). PCL/β-TCP porous scaffolds were prepared using the FDM method, and their mechanical properties were tested. The FEM simulation results were compared and validated, and the effects of porosity and pore shape on the mechanical properties were analyzed. The results of this study indicate that the PCL/β-TCP scaffold, prepared using FDM 3D printing technology for cancellous bone tissue engineering, has excellent integrity and stability. Predicting the structural stability using FEM is effective. The triangle pore structure has the most stability in both simulations and tests, followed by the rectangle and honeycomb shapes, and the diamond structure has the worst stability. Therefore, adjusting the porosity and pore shape can change the mechanical properties of the composite scaffold to meet the mechanical requirements of customized tissue engineering.

Carbon black based self-sensing cement composite for structural health monitoring – A review on strength and conductive characteristics

Even though concrete buildings have high strength and durability, they are susceptible to damage from hazards, aging, etc. In concrete structures, carbon-based conductive compounds with the potential to increase the electrical conductivity of concrete are preferred. However, it was extremely difficult to handle the high cost that prevented the widespread use of conductive materials in concrete. Carbon black, a low-cost carbon-based conductive substance supports the development of self-sensing cement composite, which has significant applications in Structural Health Monitoring (SHM). This review concentrates on the alteration of compressive strength, split tensile strength, flexural strength and conductive characteristics of concrete properties using carbon black. Utilizing a scanning electron microscope (SEM), the volume and shape of porosities inside the carbon-black embedded cement composite were analyzed. The review revealed that self-sensing cement composite based on carbon black has high durability, cheap cost, and sensitivity. The analysis found that the carbon content, size, and conductivity of the carbon black utilized significantly impact the piezoresistivity of cement composites. Nevertheless, with an increase in carbon black concentration and under conventional curing, cement composites' compressive strength and flexural strength are significantly diminished. The conductivity of the cement composite is directly proportional to the concentration of carbon black; however, the piezoresistivity of the cement composite is not considerably attained beyond the percolation threshold. The review concludes that, despite the inclusion of carbon black with acceptable strength and good sensing characteristics, the carbon-black embedded self-sensing cementitious composite is an appropriate material for structural health monitoring of various concrete infrastructures under various environmental conditions.

Modeling comparison and theoretical study of mass transfer characteristics for desiccant coated air channel under isothermal dehumidification

Coupled heat and mass transfer phenomena are encountered in desiccant coated dehumidifier, and their numerical modeling is becoming indispensable. In this study, three conjugate heat and mass transfer models were compared to clarify the effects of interparticle mass transfer and local kinetic non-equilibrium on modeling accuracy, and the models were validated by experiment results of silica gel and FAM Z01 coated dehumidifiers with single one air channel. Furthermore, a parametric study on the separate mass transfer characteristics of the dehumidifier under isothermal dehumidification was conducted based on one of the improved models. Results demonstrated that the effect of interparticle mass transfer should be involved, while the local kinetic non-equilibrium tends to be considered for desiccants with steep isotherm shape. Parametric study revealed that as air velocity increases, both air- and solid-side mass transfer change significantly, while desiccant layer thickness, interparticle porosity and isotherm shape mainly affect solid-side mass transfer. The average mass transfer Biot numbers Bim of desiccant layer with relative low thickness of 0.1 mm under various parameters are in the same order of magnitude as 1, indicating that the mass transfer resistance on solid side cannot be ignored generally.

Supersolidus liquid phase sintering of water-atomized low-alloy steel in binder jetting additive manufacturing

This work investigates the feasibility of net shape manufacturing of parts using water-atomized (WA) low-alloy steel with comparable densities to conventional powder metallurgy parts via binder jetting additive manufacturing (BJAM) and supersolidus liquid phase sintering (SLPS). In this study, a modified water-atomized powder grade with similar composition as MPIF FL-4405 was printed and pressure-less sintered under a 95% N2–5% H2 atmosphere. Combinations of two different sintering schedules (direct-sintering and step-sintering) and three different heating rates (1, 3, and 5 °C/min) were applied to study the densification, shrinkage, and microstructural evolution of BJAM parts. This study demonstrated that, although the green density of the BJAM samples was ∼42% of the theoretical density, the sintered parts experienced large linear shrinkage up to ∼25% and reached ∼97% density without compromising shape fidelity. This was ascribed to a more homogeneous pore distribution throughout the part before ramping up to the SLPS region. The synergistic effects of carbon residue, the slow heating rate, and the additional isothermal holding stage at the solid-phase sintering region were determined to be the key factors for sintering BJAM WA low-alloy steel powders with resulting minimal entrapped porosity and good shape fidelity.

Experimental test and PFC3D simulation of the effect of a hole on the tensile behavior of concrete: A comparative analysis of four different hole shapes

In this article, the effects of porosity and its geometry on tensile features of concrete were investigated, using the Brazilian test and three dimensions PFC model. In the first step, the PFC sample was calibrated by indirect tensile lab outcomes and uniaxial compression test outputs. In the next step, indirect tensile tests were done on the models consisting of various pore shapes. Cylindrical models consisted of internal pores with different shapes such as rectangular, circular, horizontal notch, and vertical notch. The diameter and or the length of these porosity changes in various values, i.e., 10 mm, 20 mm, and 30 mm. Twelve different configurations of samples were prepared by varying the porosity shapes. The mechanical behavior of samples has been provided in form of stress–strain curves at a constant and slow loading rate of 0.05 mm/min for ensuring the static condition based on Newton’s first law. Concurrent with numerical simulation, an experimental test was done on the concrete slabs containing different pores. The outcomes showed that porosity geometry plays an important role in the fracturing pattern. It was found that the porosity geometry has potent consequences on fracturing process stress and the value of the UCS for rocks. Numerical simulation shows that fracture energy decreased by increasing the dimension of the defect. Crack initiation stress was close to final stress in vertical notch configuration while the difference between the final stress and crack initiation stress has a high value for horizontal notch configuration. The sharper the hole tip, the faster the progressive failure occurred.

Internal and interfacial microstructure characterization of ice droplets on surfaces by X-ray computed tomography

HypothesisCharacterizing the microstructure of an ice/surface interface and its effect on the icephobic behavior of surfaces remains a significant challenge. Introducing X-ray Computed Tomography (XCT) can provide unprecedented insights into the internal (porosity) and interfacial structures, i.e. wetting regime, between (super)hydrophobic surfaces and ice by visualizing these optically inaccessible regions. ExperimentsFrozen droplets with controlled volume were deposited on top of metallic and polymeric substrates with different levels of wettability. Different modes of XCT (3D and 4D) were utilized to obtain information on the internal and interfacial structure of the ice/surface system. The results were supplemented by conventional surface analysis techniques, including optical profilometry and contact angle measurements. FindingsUsing XCT on ice/surface systems, the 3D and 4D (imaging with temporal resolution) structural information can be visualized. From these datasets, qualitative and quantitative results were obtained, not only for characterizing the interface but also for analyzing the entire droplet/surface system, e.g., measurement of porosity size, shape, and location. These results highlight the potential of XCT in the characterization of both droplets and substrates and proves that the technique can aid to develop hydrophobic surfaces for use as icephobic materials.

Effect of Randomness of Parameters on Amplification of Ground Motion in Saturated Sedimentary Valley

Based on Biot’s theory and the indirect boundary element method (IBEM), the Monte Carlo method is utilized to generate random samples to calculate the displacement response of a saturated sedimentary valley under SV wave incidence. The purpose of this paper is to explore the effects of randomness of porosity, permeability coefficient, and geometric shape on the seismic amplification effect of saturated complex sites. It is shown that the change of media porosity in the saturated site with defined boundary has relatively little influence on the ground motion, and the influence of the permeability coefficient is slightly larger. While in the site with a random boundary, the influence of both the porosity and permeability coefficient are significant, which cannot be ignored. The conclusion plays an important guiding role in earthquake disaster prevention and mitigation, such as seismic risk analysis and earthquake microzonation in saturated sedimentary valleys.

Prospects for the use of rock crushing screenings from Karelia as a filtering medium

The aim of the research was to study the crushing screenings of gabbrodolerite, quartzite sandstone, and quartzite stored in the pit dumps in the Prionezhsky District of Karelia in order to assess their applicability as non-traditional filtering media in water treatment for the removal of various pollutants. The use of optical microscopy and X-ray diffraction analysis allowed establishing qualitative and quantitative mineral compositions of the screenings studied. According to the results of the study of physical and chemical parameters and the total specific effective activity of natural radionuclides in the screenings, the 0.5–2.0 mm fraction meets the requirements set by the standard for natural granular filtering materials. A comparison of the materials studied with quartz sand (provided by CJSC Pogranskoye Quarry Association) confirmed that their filtering media porosity and grain shape coefficient values are not inferior to those of the standard material. The bulk density of the screenings at 1307–1550 kg/m3 is comparable to the density of the sand at 1650 kg/m3. It seems reasonable to place these screenings in the lower layer of two-layer filter systems and to use them for water clarification and for the removal of mechanical impurities and iron from water. The 2–5 mm fraction of the screenings studied may be used as a loose anti-icing material for treating road surfaces in winter. Introduction of screenings as non-traditional filtering media for water treatment at local mining enterprises contributes to more comprehensive deposit development and helps solving certain economic and environmental problems in the region.

Pore structure and its effect on acoustic velocity and permeability of reef-shoal carbonates in the Tarim Basin, Northwest China

Abstract Experiment and numerical simulation are integrated to investigate the effects of pore structure on physical properties in reef-shoal carbonate samples from the Tarim Basin. The results show three correlation trends between pore structure parameters and physical properties, which closely depend on the pore structure type. The acoustic velocity of the fractured-vuggy type (Structure I) is mainly affected by porosity and pore shape, whereas the fractured and tight types (Structures II and III) are controlled by the pore connection and fractures, respectively. For permeability, the main controlling factor of Structures I and III is porosity, whereas that of Structure II is the volume fraction of fractures. From the pore structure classification, combining pore structure parameters and porosity significantly improves the predictions of acoustic velocity and permeability, confirming that pore structure classification should be prioritized and determining the main controlling factors is critical for the improvement of acoustic velocity and permeability predictions. These results allow better exploration and development of reef-shoal carbonate reservoirs using seismic and acoustic log data.

Annealing Temperature Effects on Humidity Sensor Properties for Mg0.5W0.5Fe2O4 Spinel Ferrite.

The effects of annealing temperature on the structural, physical and humidity sensing properties of stoichiometric Mg0.5W0.5Fe2O4 spinel ferrite are investigated. In order to highlight the influence of sintering temperature on the structural, magnetic and electrical properties, ferrite samples were sintered for 2 h at 850 °C, 900 °C, 950 °C, 1000 °C and 1050 °C and the physical properties and humidity influence on magnesium-tungsten ferrite materials were analyzed. X-ray diffraction investigations confirmed the formation of magnesium-tungsten ferrite in the analyzed samples. SEM micrographs revealed the influence of annealing temperature on the microstructures of the samples and provided information related to their porosity and crystallite shape and size. This material, treated at different temperatures, is used as an active element in the construction of capacitive and resistive humidity sensors, whose characteristics were also investigated in order to determine the most suitable sintering temperature.

The impact of infill percentage and layer height in small-scale material extrusion on porosity and tensile properties

Material extrusion additive manufacturing is prone to introducing porosity within the structure due to the layer-by-layer construction using elliptical beads of material. This open porosity ultimately plays a role in determining the mechanical properties of printed parts. The shape, size, and amount of porosity within a printed part is influenced by a variety of factors, including nozzle diameter, infill percentage, layer height, raster orientation, and print speed. While several studies have investigated these and other parameters’ effects on mechanical performance and porosity, better understanding the interconnected relationships is crucial in balancing the various input parameters to achieve maximum strength. This work initially examined the influence of key print parameters (infill percentage and layer height) on the internal porosity of a printed Acrylonitrile Butadiene Styrene (ABS) part. Then, the print parameters and internal porosity were statistically correlated to final mechanical properties. Porosity was further classified as either open or closed to differentiate between connected voids in the mesostructure from isolated voids within the material itself. Mechanical performance increased with an increasing density and infill percentage, displaying a 224 % increase in elastic modulus and a 150 % increase in ultimate tensile strength. The contribution of layer height was found to be conditional upon the infill percentage.

The design and evaluation of bionic porous bone scaffolds in fluid flow characteristics and mechanical properties

Background and objectiveAt present, there is a lack of efficient modeling methods for bionic artificial bone scaffolds, and the tissue fluid/nutrient mass transport characteristics of bone scaffolds has not been evaluated sufficiently. This study aims to explore an effective and efficient modeling method for biomimetic porous bone scaffolds for biological three-dimensional printing based on the imitation of the histomorphological characteristics of human vertebral cancellous bone. The fluid mass transport and mechanical characteristics of the porous scaffolds were evaluated and compared with those of a human cancellous bone,and the relationship between the geometric parameters (e.g., the size, number, shape of pores and porosity) and the performence of biomimetic porous bone scaffolds are revealed. MethodsThe bionic modeling design method proposed in this study considers the biological characteristics of vertebral cancellous tissue and performs imitation and design of vertebrae-like two-dimensional slices images.It then reconstructs the slices layer-by-layer to form porous scaffolds with a three-dimensional reconstruction method, similar to computed tomography image reconstruction. By controlling the design parameters, this method can easily realize the formation of plate-like (femoral cancellous bone-like) or rod-like (vertebral cancellous bone-like) porous scaffolds. The flow characterization of porous structures was performed using the computational fluid simulation method. ResultsThe flow characterization results showed that the permeability of the porous scaffolds and human bone was 10−8∼10−9m2,and when the porosity of the porous scaffolds was higher than 70%, the permeability was higher than that of human vertebrae with a porosity of 82%. The maximum shear stress of the designed porous scaffolds and human vertebra were less than 0.8Mpa, which was conducive to cell adhesion, cell migration, and cell differentiation. The results of 3D printing and mechanical testing showed good printability and reflected the relationship between the mechanical properties and design parameters. ConclusionsThe design method proposed in this study has many controllable parameters, which can be adjusted to generate diversified functional porous structures to meet specific needs, increase the potential of bone scaffold design, and leave room for meeting the new requirements for bone scaffold characteristics in the future.

Characterisation of defects in die cast aluminium parts

In this paper, the results of computed tomography and destructive testing of a die cast, gas tight aluminium part are compared and analysed with the aim of refining the porosity map. The mapping of the continuity defects detected by the two methods makes it possible to estimate the number, shape and distribution of continuity defects on and in the immediate vicinity of the machined surface, and to compare the characteristics of continuity defects detected by non-destructive and sequential fine machining. Based on the results of the CT scan of a given casting, we also performed destructive testing to find defects in a selected part of the casting by sequential fine machining. The basic criterion for the choice of the cutting parameters was to minimize the plastic deformation (smearing) on the machined surface, i.e. to clearly identify porosity. We then investigated the position, shape and other characteristics of porosity on the surfaces. The results and differences resulting from the two different methods are also analysed.