Porosity Shape Research Articles

Bending and free vibration analysis for FGM plates containing various distribution shape of porosity

In this paper hyperbolic shear deformation plate theory is presented for bending and the free vibration of functionally graded plates with considering porosities that may possibly occur inside the functionally graded materials (FGMs) during their fabrication. Four different porosity types are used for functionally graded plates. Equations of motion are derived from Hamilton's principle. In the solution of the governing equations, the Navier procedure is implemented. In the numerical examples, the effects of the porosity parameters, porosity types and geometry parameters on the bending and free vibration of the functionally graded plates are investigated. It was found that the distribution form of porosity significantly influence the mechanical behavior of FG plates, in terms of deflection, normal, shear stress and frequency.

Terahertz time-domain spectroscopy for powder compact porosity and pore shape measurements: An error analysis of the anisotropic bruggeman model

Terahertz time-domain spectroscopy (THz-TDS) is a novel technique which has been applied for pore structure analysis and porosity measurements. For this, mainly the anisotropic Bruggeman (AB-EMA) model is applied to correlate the effective refractive index (neff) of a tablet and the porosity as well as to evaluate the pore shape based on the depolarisation factor L. This paper investigates possible error sources of the AB-EMA for THz-TDS based tablet analysis. The effect of absorption and tablet anisotropy – changes of pore shape with porosity and density distribution – have been investigated. The results suggest that high tablet absorption has a negligible effect on the accuracy of the AB-EMA. In regards of tablet anisotropy the accuracy of the porosity determination is not impaired significantly. However, density distribution and variations in the pore shape with porosity resulted in an unreliable extraction of the tablet pore shape. As an extension of the AB-EMA a new concept was introduced to convert the model into bounds for L. This new approach was found useful to investigate tablet pore shape but also the applicability of the AB-EMA for an unknown set of data.

Non-graphitizable resin coating on polyacrylonitrile-based polyHIPE to prepare high surface area graphitic carbon foam and the investigation of its electrochemical performance as an anode of lithium-ion batteries

A novel facile route was proposed for low-temperature stabilization of polyacrylonitrile (PAN)-based polyHIPE polymers to prepare high surface area graphitic carbon foam (CF) under mild carbonization conditions. In this respect, poly(acrylonitrile-co-divinylbenzene) foams with a distinctive microstructure of polyHIPE foams were coated by a non-graphitizable resin to eliminate the complicated and high-temperature stabilization process before pyrolysis. The prepared nanoporous CFs were characterized by different techniques including nitrogen sorption analysis, Raman spectroscopy, scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM). Experimental results revealed that the proposed strategy successfully preserved the foam framework and porosity shape after pyrolysis at 900 °C. The prepared CFs exhibited a high BET specific surface area and a pore volume of 879 m2 g−1 and 0.59 cm3 g−1, respectively. The Raman spectroscopy and HR-TEM results confirmed the successful stabilization and the formation of graphitic domains in the CFs. The obtained CFs when utilized as an anode of Li-ion batteries (LIBs), and showed improved rate capabilities compared to a commercial graphite anode and stable cycle performance up to several hundred cycles. The results revealed the potential applications of the prepared CFs in the batteries specialized for high-power devices.

Particle shape influence on the deformation resistance of carbonate sands under drained condition

The carbonate sand has high porosity and irregular particle shape compared with the quartz sand. Under dynamic loads, the carbonate sand perhaps experiences drained or partial drained shear, and the contribution of particle shape to its deformation resistance was still unrevealed. In this paper, particle shapes of five samples were first quantitively evaluated. Then, monotonic and cyclic tests under drained condition were carried out based on the simple shear apparatus. The particle size and shape were quantitively measured after the tests, and the particle breakage degree and its breakage mode were discussed. It is found that before phase transformation points (PT points), the irregular particles mobilize greater shear resistance. The particle breakage reduces the deformation resistance after the PT point due to its depression effect on the volume shear dilation. In cyclic shear, irregular particles have larger volume contraction due to the particle breakage, and the surface grinding is the major breakage mode. Under the same cyclic stress ratio (CSR), the irregular particles show smaller shear strain amplitudes, indicating that the irregular particles have stronger resistance to deformation. It is also found that the particle shape mainly influences the deformation resistance when the overall regularity (OR) is less than 0.8.

The Dielectric Function of “Astrodust” and Predictions for Polarization in the 3.4 and 10 μm Features

Abstract The dielectric function of interstellar dust material is modeled using observations of extinction and polarization in the infrared, together with estimates for the mass of interstellar dust. The “astrodust” material is assumed to be a mix of amorphous silicates and other materials, including hydrocarbons producing an absorption feature at 3.4 μm. The detailed shape of the 10 μm polarization profile depends on the assumed porosity and grain shape, but the 10 μm spectropolarimetric data are not yet good enough to clearly favor one shape over another, nor to constrain the porosity. The expected 3.4 μm feature polarization is consistent with existing upper limits, provided the 3.4 μm absorption is preferentially located in grain surface layers; a separate population of non-aligned carbonaceous grains is not required. We predict the 3.4 μm polarization feature to be (Δp)3.4 μm/p(10 μm) ≈ 0.016, just below current upper limits. Polarization by the same grains at submillimeter wavelengths is also calculated.

ACOUSTIC PERFORMANCES OF METAL SAMPLES MANUFACTURED BY ADDITIVE TECHNOLOGIES

Porous materials (PMs) have been widely used since the development of powder metallurgy. PM samples are obtained by various methods, while the structure varies from sample to sample. Deviation from a given structure leads to a deviation of the specified properties up to 30%, including acoustic. Selective laser melting (SLM), allows to obtain samples with a low structural deviation (up to 13%) in a wide porosity range P=0.3-0.7. An increase in the sound absorption coefficient and the expansion of the frequency range allows to use such samples in noise reduction units’ designs. Nine samples with different porosity and cell shape were obtained by the SLM method with the use of AlSi10Mg aluminum powder obtained by gas atomization and BB751P nickel powder obtained by plasma centrifugal spraying. The porosity of the samples (P) varied in the range (0.3–0.7), the diameter was D = 34.5 mm, and the height varied in the range of 15–45 mm. The acoustic characteristics comparison of traditional PMs with porous fused material (PFM) by the sound absorption index shows that PM, as a rule, are superior to PFM, while it is approximately equal to porous cast

Modeling of Superelastic–plastic Behavior of Porous Shape Memory Alloys Incorporating Void Shape Effects

A new constitutive model for describing the superelastic–plastic behavior of porous shape memory alloys (SMAs) is proposed. The model incorporates the influences of void shape and hydrostatic pressure as well as the elastic modulus mismatch between austenite and martensite. In addition, the interactions between plastic strain and transformation strain are considered via the plastic back stress. The porous SMAs are considered as two-phase composites with the dense SMA matrix and the second phase representing ellipsoidal voids. Based on Gurson’s formulation, the transformation and plastic flow potentials accounting for the transformation–plasticity coupling are developed. The numerical results present good agreement with available experimental data for various levels of porosity, which proves that the model is capable of capturing stress-induced phase transformation and plastic deformation of porous SMAs. Using the proposed model, the influence of plastic strain on reverse transformation and the effects of porosity and void shape on the pseudoelastic and plastic behavior of porous SMAs are investigated.

Linking elastic and electrical properties of rocks using cross-property DEM

SUMMARY Combining electrical and elastic measurements can be instrumental in lowering the uncertainty of subsurface characterization. Many commonly used rock physics relations for joint electrical–elastic properties are at least partly empirical and often rely on the estimation of porosity as an intermediate step. We combine differential effective medium schemes that relate, respectively, elastic and electrical properties to porosity and pore shape. The resulting expressions are independent of porosity, depending only on pore aspect ratio. Analysis of published joint electrical–elastic data shows that a single aspect ratio model performs well for clean sandstones, allowing us to model Vp/Vs ratios as a function of resistivity. Clay-bearing sandstones are more complex, but our modelling can still identify the correct trends. We speculate about the potential to extend our approach to produce additional cross-property relations.

Effects of spatial energy distribution-induced porosity on mechanical properties of laser powder bed fusion 316L stainless steel

Laser powder bed fusion (LPBF) additive manufacturing (AM) offers a variety of advantages over traditional manufacturing, however its usefulness for manufacturing of high-performance components is currently hampered by internal defects (porosity) created during the LPBF process that have an unknown impact on global mechanical performance. By inducing porosity distributions through variations in print energy density and inspecting the resulting tensile samples using computed tomography, nearly 50,000 pores across 75 samples were identified. Porosity characteristics were quantitatively extracted from inspection data and compared with mechanical properties to understand the strength of relationships between porosity and global tensile performance. Useful porosity characteristics were identified for prediction of part performance. Results indicate that ductility and strain at ultimate tensile strength are the global tensile properties most significantly impacted by porosity and can be predicted with reasonable accuracy using simple porosity shape descriptors such as volume, diameter, and surface area. Moreover, it was found that the largest pores influenced behavior most significantly. Specifically, pores in excess of 125 µm in diameter were found to be a sufficient threshold for property estimation. These results establish an initial understanding of the complex defect-performance relationship in AM 316L stainless steel and can be leveraged to develop certification standards and improve confidence in part quality and reliability for the broader set of engineering alloys.

A Review Study on the Main Sources of Porosity in Al‐Si Cast Alloys

The present study was performed on A356 and B319 alloys in mechanically stirred or degassed condition. Melts were Sr‐modified and grain‐refined. Hydrogen content was varied from less than 0.1 ml/100 g Al to ∼0.4 ml/100 g Al; Fe was increased to 0.8% in B319 alloy. Lanthanum and cerium were added as 99.5% pure metals. Two main techniques were used to investigate porosity formation: fracture surface of tensile or fatigue test bars, or reduced pressure test (RPT) method. Porosity type and shape were examined. The results show that pore size is more influential than small scattered ones from a mechanical point of view. Tensile testing is affected by porosity located at the center of the testing bar, whereas edge porosity is responsible for crack initiation in case of fatigue testing. Intermetallics precipitate in the form of intercepted platelets which restricts the flow of the molten metal, leading to formation of shrinkage cavities. Precipitation of clusters of compounds from the liquid state such as Al2Si2Sr, Mg2Sn, Al3Ti, or added Al2O3particles would as well act as nucleation sites for porosity formation. Most oxides were observed in the form of long branched strings. In some cases, bifilms were also reported in addition to SrO and MgO.

Application of TPMS structure in bone regeneration

Bone defect repair, due to its complex process in nature, has become a costly issue in modern day medicine. This causes a growing demand for a bone substitute that is effective and easy to construct. Recently, triply periodic minimal surface (TPMS) scaffolds, which embody trabecular bone-mimicking hyperboloidal topography, have become a promising candidate for this exact role due to their unique structure to promote many cellular processes. In response to the growing popularity of TPMS scaffolds amongst researchers, this review discusses the effect of different parameters (including pore size, porosity, and pore shape, as well as their influences on mechanical property, permeability, and curvature), along with the controlling and designing of such parameters, on bone regeneration to serve as a guide for future researchers in designing and utilizing TPMS scaffolds for bone regeneration purposes.

Rotor-dynamic performance of porous hydrostatic thrust bearing operating under magnetic field

Purpose The porous bearings are commonly used in slider thrust bearings owing to their self-lubricating properties and cost effectiveness as compared to conventional hydrodynamic bearings. The purpose of this paper is to numerically investigate usefulness of porous layer in hydrostatic thrust bearing operating with magnetic fluid. The effect of magnetic field and permeability has been analysed on steady-state (film pressure, film reaction and lubricant flow rate) and rotor-dynamic (stiffness and damping) parameters of bearing. Design/methodology/approach Finite element approach is used to obtain numerical solution of flow governing equations (Magneto-hydrodynamics Reynolds equation, Darcy law and capillary equation) for computing abovementioned performance indices. Finite element method formulation converts elliptical Reynolds equation into set of algebraic equation that are solved using Gauss–Seidel method. Findings It has been reported that porosity has limited but adverse effects on performance parameters of bearing. The adverse effects of porosity can be minimized by using a circular pocket for achieving better steady-state response and an annular/elliptical pocket, for having better rotor-dynamic response. The use of magnetic fluid is found to be substantially enhancing the fluid film reaction (53%) and damping parameters (55%). Practical implications The present work recommends use of circular pocket for achieving better steady-state performance indices. However, annular and elliptical pockets should be preferred, when design criteria for the bearing are better rotor-dynamic performance. Originality/value This study deals with influence of magnetic fluid, porosity and pocket shape on rotor-dynamic performance of externally pressurized thrust bearing. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2020-0289/

Design, analysis, fabrication and testing of PC porous scaffolds using rapid prototyping in clinical applications

Introduction and Aim: Rapid prototyping is an advanced fabricating method, where three dimensional objects are built precisely from their three-dimensional computer aided design models in a very short duration. In contrast to traditional machining methods, most of the rapid prototyping techniques tend to fabricate parts based on additive manufacturing process. Fabrication of biomaterial into 3-D scaffold structures is the next vital step in the development of bone implants depending on bone injuries of individual patients, and it is highly demanding among the Indian orthopedic surgeons for treating those bone related defects. Therefore, the need for reliable and economically feasible design, better biomaterials, and efficient fabrication method for scaffold to treat musculoskeletal defects has increased in recent years.
 Materials and Methods: Investigation of scaffold for porous structured bone implant is a recently emerging field in medicine and is involved in developing artificial bones like structure using materials like Tri Calcium Phosphate (TCP), Polyether ether ketone (PEEK), Hydroxyapatite (HA), Polycaprolactone, polycarbonate (PC), poly (l-lactide) PLLA or Polyamide (PA) etc., by incorporating pores in the scaffold. In this research, the samples of the scaffold specimens were designed and fabricated using Stereo lithography technique with biocompatible PC resin and the strength of each sample were analyzed.
 Results: The porous scaffold models are structured with different designs utilizing the CAD software. The porous scaffold with various porosity and pore shape is analyzed through Finite Element Analysis (FEA). StereolithographyViperSi2 method was utilized to manufacture the polycarbonate scaffold. The manufactured rhombus pore model shows the stress value esteems around 200 MPa¸ which is nearest to the compressive strength of human bone. Subsequently the rhombus pore model gives better mechanical load bearing capacity when implanted for tissue recovery in bones.
 Conclusion: Bisphenol-A Polycarbonate material give better surface completion, 100% pore interconnectivity and new tissue arrangement of the fabricated porous scaffold. The SLA technique offers the more noteworthy load bearing quality and great exactness of the fabricated scaffold.

Developing an improver of targeted action for the prolonged freshness of bread made from wheat flour

The development of a complex bakery improver CDP (Ukraine) to slow down the staling of products developed for accelerated technologies is urgent. It contains nutritional supplements with GRAS status. Whey protein concentrate CDP-UV-65 was chosen as a functional basis. The active part contains the enzyme preparation Novamil 1500MG, maltodextrin, defatted sunflower lecithin, carboxymethyl cellulose, apple pectin, dry wheat gluten and ascorbic acid. It is proved that with rational dosage of the developed complex bakery improver in the amount of 1.5% to the flour mass, the bread production process is reduced by 180 minutes. It has been established that the bread Freshness, the recipe of which includes the developed improver, is characterized by a higher specific volume by 10.1% in comparison with the control, porosity, and better shape stability of hearth products. It has been proven that products with the addition of the CDP SUPER complex bakery improver retain freshness longer, which is confirmed by a 47% greater total crumb deformation compared to the control. The inhibition of staling in bread Freshness occurs due to the accumulation of dextrin by 27.1% compared with the control. Thus, the total content of dextrins in wheat bread is 1.918% to DS, and in Milk bread - 2.438% to DS. The research results prove the expediency of using the complex bakery improver CDP in the technology of wheat bread in order to extend the preservation period of its freshness up to 72 hours in unpackaged form

A machine learning framework to predict local strain distribution and the evolution of plastic anisotropy & fracture in additively manufactured alloys

Machine learning (ML) approaches are widely used to develop systems or frameworks with the ability to predict the properties of interest by learning and establishing relationships and inferences from data. In the present work, an ML based framework is proposed to predict the evolution of local strain distribution, plastic anisotropy and failure during tensile deformation of AlSi10Mg aluminum alloy produced by selective laser melting (SLM). The framework combines the methods involved in additive manufacturing (AM) and artificial intelligence (AI). This includes printing of test specimens using laser powder bed fusion (LPBF), x-ray computed tomography (CT) scanning to measure internal defects distribution, mechanical testing with digital image correlation (DIC) to get local strain evolution, extraction and coupling of CT and DIC data, and the development, validation and evaluation of an artificial neural network (ANN) model. The experimental data from CT and DIC measurements are used to train, validate and evaluate the proposed ANN model. Microstructural features such as the size, shape, volume fraction and distribution of porosity are used as an input to ANN. The proposed ANN model successfully predicts the evolution of local strains, plastic anisotropy and failure during tensile deformation. The intensity and location of strain hotspots as well as the shape of shear bands and the location of crack initiation are well predicted. The current research demonstrates the applicability of an ML based ANN approach to predict microstructure – property – performance relationships for engineering materials with intricate heterogeneous microstructures such as those produced additively by SLM. The success of the present approach motivates further use of ML techniques, as a mean for accelerated development of new alloys, AM process optimization and its wide scale applicability.

New fast synthesis of MOF-801 for water and hydrogen storage: Modulator effect and recycling options

We report a new simple, fast, scalable technique for MOF-801 synthesis. The effect of modulators on crystallinity, size, and shape of particles, porosity, hydrogen and water uptake was traced using two mono-carboxylic acids with various concentrations. We also showed that slow heating and small grains in powder samples are optimal for fast water release at relatively low temperatures. Heating up to 60–80 °C is enough for complete water release in 40 min, while at 40 °C, after 100 min, water is retained in pores of the sorbent. It was shown that both acetic and formic acids enhance the properties of MOF-801 material. However, even without any additives, proposed synthesis conditions lead to porous, highly crystalline material with hydrogen uptake about 1.1 wt% at 750 mmHg and water uptake about 20% at ambient conditions. We proved that solvent from the synthesis of MOF-801 could be used at least four times without any degradation of the obtained sorbent in key properties.

Porous an hollow nanofibers for solid oxide fuel cell electrodes

Among the diverse approaches for improving the electrode performance of solid oxide fuel cells operating at intermediate temperatures, the use of nanofiber-based electrodes has provided large improvement owing to their large specific surface area, continuous conduction pathway, and highly porous structure. However, the low thermal stability at increased temperature often limits the process compatibility and sustainability during operation. In this study, we fabricated nanofiber-based electrodes with a high porosity and hollow shape using one-step electrospinning with a hydrogel polymer, which exhibited largely improved performance and excellent thermal stability. A porous-nanofiber-based cell exhibits a polarization resistance of 0.021 Ωcm2 and maximum power density of 1.71 W/cm2 at 650 °C, which is an improvement of 34.3% and 14.7% compared to that of a solid-nanofiber-based cell, respectively. Comprehensive analyses of the microstructures and chemistry indicate that the performance increase is mainly attributable to the enhanced surface oxygen exchange reactions owing to the extended reaction sites with lower energy barriers by the high porosity and enriched oxygen vacancies in the nanofibers.

Crack Effect on the Equivalent Thermal Conductivity of Porously Sintered Silver

Characterizations of equivalent thermal conductivity (ETC) of sintered silver is an important topic due to the thermal–mechanical reliability requirements of electronic packaging. In this paper, the effect of various types of cracks on the ETC of sintered silver are discussed. A numerical method to simulate the heat transfer behaviors of porous sintered silver containing the crack effect is presented. The results show that the ETC of sintered silver depends significantly on the crack length, crack orientation, porosity, and pore shape. Theoretical formulae to estimate the ETC of sintered silver are also presented, in which the effects of arbitrary crack depth, arbitrary crack orientation, arbitrary porosity, and arbitrary pore shape factor on ETC are included. It has been found that the influence of the side edge crack on the reduction of the ETC of sintered silver is the most obvious compared with the center crack and the upper edge crack. This study presents a quantitative method to evaluate the crack effect on the ETC of porous sintered silver.

Al foams manufactured by PLA replication and sacrifice

A new method for the manufacturing of pre-determined open porosity Al foams is presented in this work. Starting from a 3D foam model designed with CAD and printed with fused deposition modeling (FDM), a porous structure of poly lactic acid (PLA) has been replicated. The choice of this material has been driven by the properties in terms of recyclability and low cost. The truncated octahedron for the porosity shape has been selected due to benefit and properties ascribable to its morphology. After creating the 3D PLA model, it has been filled with liquid plaster. After its solidification, PLA is removed in oven at 600 °C so that a negative-shaped plaster mold is obtained. Successively liquid Al at 750 °C is poured in the mold inside the oven. After Al solidification, plaster can be easily removed in ultrasonic bath thus obtaining Al foam with the same morphology of the starting PLA model. This process shows great flexibility allowing to manufacture different kind of elementary cell types. Tailoring of the selected properties of the manufactured foams, e.g. the morphology, the density or the surface/volume ratio may be obtained. With this technique many other metals and alloys can be manufactured too. The potential of this production technique can be successfully employed in many application fields of metal foam. Light-weight 3D lattice structures are widely employed for multifunctional applications such as loading bearing, negative and zero thermal-expansion structures, vibration attenuation, impact and blast proof structures.

Efficient mineralization and osteogenic gene overexpression of mesenchymal stem cells on decellularized spinach leaf scaffold.

Until now, various methods have been introduced to fabricate 3D scaffolds to provide a suitable substrate for cell growth and proliferation and subsequent use in tissue engineering to repair damaged tissues. The 3D scaffolds can simulate the natural cellular microenvironment well. Herein, the decellularized leaf spinach has been used which not only have no problems associated with artificial scaffolds, but they also do not cost significantly. Decellularized scaffolds surface properties were characterized by the investigation of scaffolds surface roughness, hydrophilicity, mechanical properties, size and shape of porosities and specific surface area. In the next step, osteogenic differentiation potential of bone marrow derived mesenchymal stem cells cultured on the scaffold and culture plate (as a control) was evaluated using alizarin staining and calcium content, alkaline phosphatase activity and bone related genes expression assays. The results indicated that the surface properties and shape of scaffold pores were effective in the stem cells binding, growth and proliferation. This higher biocompatibility due to the ideal surface hydrophilicity as well as high specific surface area due to the presence of a rough grid surface ultimately increased the efficiency of stem cell's bone differentiation. Taken together, it can be concluded that the decellularized spinach leaf scaffold, due to its easy availability, low prices and high efficiency, can be considered as a promising potential candidate for use as a proper substrate for stem cell growth and differentiation in bone tissue engineering.