Porosity Fraction Research Articles

Age-at-death estimation based on micro-CT assessment of pubic symphysis: Potentially new methodological approach

BackgroundAlthough various methods for age-at-death estimation of skeletal remains are available, this is still an unsolved issue in forensic anthropology, especially concerning elderly individuals. Moreover, the lack of population-specific methods often made age-at-death estimation unreliable in other populations. AimOur study aimed to examine whether micro-computed tomography (micro-CT) analysis of pubic bone samples obtained from the contemporary Serbian population could be used in anthropological and forensic practice for age-at-death estimation. MethodologyThis study encompassed 62 pubic samples obtained from 26 adult male and 36 adult female cadaveric donors (age range: 22–91 years). Initially, staging according to the Suchey–Brooks phases was performed by two experienced investigators, followed by micro-CT assessment of pubic bone trabecular and cortical compartments (spatial resolution of the scans was 10 µm). ResultsOur results revealed an age-associated decline in trabecular and cortical micro-architecture of elderly male and female individuals, with the most prominent changes present in trabecular bone volume fraction and total porosity of the anterior and posterior cortical surface of the pubic bone. Those parameters were used to generate age-at-death estimation equations. One sample t-test did not reveal a significant difference between estimated age-at-death and real (known) age-at-death in the overall sample (mean absolute error [MAE] of 4.76 years), female (MAE of 9.66 years) and male cadaveric donors (MAE of 6.10 years, p > 0.05). ConclusionOur data indicated that micro-architectural features of trabecular and cortical compartments of pubic bone could potentially be applied as an additional reliable method for age-at-death estimation in the Serbian population.

Tribological Behavior of Cast Aluminum Matrix Composites After Multiple Remelting

One of the limiting factors for expanding the applications of aluminum alloy castings in many high-tech industries is the insufficient level of tribological properties, especially under conditions of dry and abrasive wear. Reinforcing of aluminum alloys with hard ceramic particles, i.e., transition to aluminum matrix composites, allows significantly increasing their resistance against dry sliding friction, scuffing, and seizure in wide temperature and force intervals of operation. Among the numerous problems related to the industrial implementation of cast aluminum matrix composites, the problem of their recycling takes the important place. This work is aimed at establishing the influence of metallurgical processes during remelting on the change in tribological properties of cast Al-Si-B4C aluminum matrix composites. For this purpose, tribological tests in conditions of dry friction according to the ball-on-disc scheme were used. Reinforcing of an AlSi12 matrix alloy with B4C particles leads to a decrease in the composite friction coefficient and the mass wear in the as-cast state in comparison with an unreinforced matrix alloy. During remelting, the tribological properties of the aluminum matrix composites do not deteriorate. Repeated remelting leads to the improvement in particle distribution uniformity, formation of the Al3BC phase at the matrix/particle interfaces, fragmentation of reinforcing B4C particles due to cyclic thermal loads as well as an increase in the porosity fraction. The changes in the structural-phase composition during remelting have a direct influence on the level of tribological properties. Typical effects associated with dry friction, such as plastic deformation of the matrix material and the formation of areas of adhesion-cohesive fracture, indicative of scuffing, were revealed by SEM analysis of the wear tracks of an unreinforced matrix alloy. For the composite material, these effects manifested to a much lesser extent. A qualitatively similar sliding wear behavior was observed for all composite samples, regardless of the remelting iteration. The study suggests that the formation of a transitional tribolayer may occur during dry sliding friction of aluminum matrix composites, which can reduce the friction coefficient.

Novel composition of Nd-Fe-B gas atomized powder to produce compression bonded magnets

New compositions of Nd-Fe-B powders were produced via gas atomization. Helium and argon were used as atomizing gases. For the same process parameters, helium resulted in a powder that is 6 times finer than the powder produced with argon. In both cases, the atomization conditions were set to achieve fine powders and, therefore, fine microstructures, since this is critical to obtain a suitable coercivity. The powders were sieved to separate the fraction below 20 μm (∼90 % of powder atomized with He). The microstructure is formed by a mix of elongated and equiaxial grains with random crystallographic orientation and an average grain size of ∼ 1 μm, which was measured by Electron Backscattered Diffraction. This kind of measurements and images were taken for the first time for fine helium atomized Nd-Fe-B powders. The embedding of the powder in copper was found to be useful, as the conventional mounting in metallographic conductive resin produced charging of the sample. Annealing up to 1000 °C did not cause any significant grain growth that could deteriorate the magnetic properties. Annealing at 700 °C for 15 min improved the magnetic properties due to the crystallization of residual amorphous phase. Warm compaction was used to produce magnets with a high volume fraction of magnetic powder (>70 %) and low real porosity (∼5 %). These magnets exhibit a high remanence (∼0.5 T) and maximum energy product (∼35 kJ/m3), combined with a suitable intrinsic coercivity (>500 kA/m). The new compositions and processing route could cover a market niche. The thoroughly analyzed powders could be also suitable for some additive manufacturing technologies that require spherical powders with very specific particle size distributions.

On the origin of cracking in laser powder bed fusion processed LaCe(Fe,Mn,Si)13, and the impact of post-processing

LaCe(Fe,Mn,Si)13 magnetocaloric material printed by laser powder bed fusion (LPBF) has a huge potential for magnetic refrigeration. However, high crack and defect susceptibility in LPBF processing remains a limitation of its application. This study optimised the LPBF process parameters for optimally dense blocks. The volumetric energy density condition, EV = 250 J/mm3, showed the lowest crack density and porosity fraction. The behaviour and mechanism of different cracks and defects were revealed. The lower energy density parameter sets, caused by higher scanning speeds and hatch spacing, lead to the formation of lack-of-fusions. The hot cracking observed was attributed to stress concentration and a stable liquid film. The solid-state cracks observed were expected in the microstructure of the as-fabricated (AF) sample due to the poor toughness of the La/Ce/Si-rich phases. Thermal heat treatment and quenching increased the magnetocaloric effect (MCE) of the AF sample. The maximum magnetic entropy change (∆Smax) of the heat-treated sample was − 3.68 Jkg−1K−1 at 294 K, when applied to a 1 T field. The Curie temperature (Tc) (298 K when applied 0.01 T field) and superior MCE make the material an ideal choice for realising room-temperature magnetic refrigeration.

Non-invasive density and porosity fraction mapping of bituminous coal using ultrasound

The principle of the conventional ultrasound test states that the detectable voids cannot be smaller than the acoustic wavelength. However, by using effective medium approximation, the fraction of small voids can be estimated by the variation of the effective density. In this study, a non-contacting ultrasound-based porosity fraction mapping methodology is developed for estimated small voids in coal with long operating wavelength in air. This novel ultrasonic technique based on the mechanical properties of coal offers a rapid scan of the effective density mapping and distribution of void fraction over a large sample area, which overcame the limitation of small voids detection in the conventional ultrasound testing.

The use of computerized tomography (CT) and image processing for evaluation of the properties of foam concrete produced with different content of foaming agent and aggregate

This study measures the impact of foaming agent and aggregate content in foam concrete mixes by conducting a series of tests on material properties as well as pore formation by using micro-Computerized Tomography (CT) scanning and image processing technique. This technique allows measuring the porosity fraction of porous materials and foam concretes to comparatively evaluate the experimental versus the image processed porosity of the samples. Based on the results, it is found that the increase in aggregate content can exponentially reduce the pore connectivity of foams and enhance their physical and mechanical properties. Additionally, the proposed CT scanning and image processing approach is a proof-of-concept over the use of 3D modeling. This is done with a specific tool-kit and the results prove suitability of image processing techniques in accurately measuring pore content in foam concrete samples. Suggestions for future studies are also provided and discussed at the end of the manuscript.

Study of petrophysical parameters of productive series by use of well data

The progress of existing geophysical techniques for the last years led to a wider scope of the problems resolved using this set of tools. The tools allow tackling pivotal tasks such as the study of lithology in a geological section, correlation, evaluation of saturation, porosity, permeability, and clay fraction, and outlining of oil-gas and water-saturated layers. Complications emerging while resolving these problems directly depend on the petrophysical parameters of reservoir layers. For instance, similar values of resistivity in oil and water layers result in high value of clay fraction and variation of porosity in a wide range and this complicates distinguishing the oil and water layers. On the other hand, it is known that an increase of cementing clay amount in reservoirs causes drop of porosity (Kpor.) and increase of residual water saturation.
 This paper is devoted to design of models defining correlation between petrophysical parameters of reservoir layers by use of integrated well data and establishing regression equations from these parameters’ distributions. Models of variation of porosity, permeability, clay fraction and oil and gas saturation through the sections of wells were also designed. They made it possible to evaluate filtration-capacity characteristics and establish correlation between petrophysical parameters of reservoir layers and gain information about this field.
 The bar graph was drawn for permeability coefficient variation through studied reservoirs in Qirmaky suite (QD-1, QD-2, QD-3, QD-4) by use of sections of wells conditionally marked as 1, 2, 3, and 4 in the Balakhany field.
 Analysis of the constructed histograms allows us to classify the studied collector layers according to their permeability. Of the 17 layers studied in section of well 1, only Layer 17 has very good permeability, the other 16 are of good permeability; all 17 layers of well 2 have good permeability characteristics; of the 17 layers of well 3, Layer 3 is of poor permeability, layers 6, 7, and 14 have average permeability, and the rest are of good permeability; all 12 layers of well 4 have good permeability.
 The study target is Qirmaky suite (QD-1, QD-2, QD-3, QD-4) of the Productive Series in Balakhany field.

Effect of grain size distribution on the shear properties of sand

In this study, we investigated the effect of particle size distribution on the shear properties of sand. Direct shear tests were conducted using four types of sand samples with different particle size distributions obtained from standard sand produced by Xiamen ISO Co. Ltd. The results show that the influence of particle size distribution on the internal friction angle was significant. Typically, the internal friction angle increases with increasing the coefficient of non-uniformity (Cu) and decreasing the curvature coefficient (Cc). The discrete element results show that the initial particle size distribution significantly affects the porosity, coordination number, and particle slide fraction. In addition, the grey relation analysis revealed that the sliding fraction and coordination number have the greatest correlation with the internal friction angle. The research results of this study help to understand the changes in particle contact, internal stress, and particle sliding during the shear failure process of sand.

Analysing the effect of defects on stress concentration and fatigue life of L-PBF AlSi10Mg alloy using finite element modelling

Additive manufacturing (AM) is a developing manufacturing technology, which provides excellent attributes compared to other manufacturing techniques. However, one of the critical challenges is the presence of defects that hinder the mechanical properties of the parts, particularly the fatigue life. Experimental understanding of fatigue is a cumbersome process. Therefore, numerical prediction based on specified conditions (such as porosity and applied load) can be an alternative to experimental analysis at the design stage of AM parts. In this study, elastic–plastic finite element analysis (FEA) is performed to obtain the stress distribution around pores, and their resultant effect on fatigue life for L-PBF (laser powder bed fusion) produced AlSi10Mg alloy samples. The stress field is calculated for both single and multiple pore models, where stress concentration is evaluated as a function of the pore’s location and its size. It is found that both pore location and size affect the stress field; however, location effects dominate over pore size. For the same remote applied stress level, the stress concentration around the pore increases with an increase in pore size, and the local maximum stress occurs near the pores that are closest to the surface. The current study also evaluates the relative effect of porosity fraction, average pore size, and location. It is found that the magnitude and sensitivity of stress concentration are hierarchically controlled by porosity location, pore size, and porosity density. A multi-scale finite element (FE) model is proposed based on inherent porosity data measured using Computed Tomography (CT) to predict overall fatigue life. The fatigue cycles are calculated using the rainflow counting algorithm in FE Safe using the stress–strain data obtained from the proposed FEA model. Using the proposed model, it is possible to generate S–N curves for any loading condition for a given porosity condition (porosity density and average pore size). The S–N curve results obtained from the FE model are compared to the experimental observations. The predicted fatigue life shows approximately 5% error with experimental results at high stress loading conditions. However, the proposed model overpredicts the fatigue life at low stress loading by almost 30%.

The reservoir rock volumetric concentration and tortuosity description of pore space of Xa field, Niger Delta Basin

The assessment of rock reservoir volume concentration is necessary as it accounts for the appreciable pore spaces available for hydrocarbon and other targets. Raw well d-ata from oil wells A, B and C in some parts of the Niger Delta Basin (XA Field) were used for porosity estimates in sandstone and shale formations. Using the Microsoft Excel for analysis, gamma ray log, density log with respect to depth were generated. The results of these curves were used to estimate porosity and create models for porosity-formation factor with respect to density effect. The major findings revealed the average porosity values as about 20% for well A, 17% for well B and 19% for well C. The results show that increase in density gives rise to a decrease in porosity in both lithologies. In order to establish a relationship between porosity of this Field rock reservoir, a plot of porosity with formation factor due to density influence was necessary. These curves lead to several equations with the average for linear curves as FD= —400øXA+98.8 and FD = (–2øXA+4.9) .×10–3for fractional and percentage porosities respectively. These models show that both parameters are strongly related with coefficients of 0.9723 (for both plots from well A), 0.8274 (for both plots from well B) and 0.9689 (for both plots from well C) for XA Field. These results correspond to the non-linear relation, øXA = 0.8006 FD–0.465 0.9689as the original values of the cementation exponent and the tortuosity factor are obtained, if the formation factor is considered as the subject.

Torsional buckling response of FG porous thick truncated conical shell panels reinforced by GPLs supporting on Winkler elastic foundation

In the present research, torsional buckling response of thick truncated conical shell panels supporting on Winkler-type elastic medium has been surveyed. The shell is constructed from a porous metal material reinforced by graphene platelets (GPLs) in which the porosity and volume weight fraction of nanofillers are graded along the thickness of shell. Three functions for porosity distribution and five patterns of GPLs are examined. To estimate the Young modulus of the shell, Tsai-Halpin micromechanical model, and for its mass density, extended rule of mixture is employed. Linear theory of 3D elasticity in conjunction with the virtual work principle and numerical graded finite element method (FEM) are applied to derive the state of equilibrium in pre-buckling mode. Torsional buckling forces are derived by applying nonlinear Green strains and by deriving geometric stiffness matrix of the system. The effect of various parameters such as coefficient of porosity, various distributions of porosity and different nanofiller patterns, weight fraction of graphene nanofillers, semi vertex angle of cone, span angle, stiffness of elastic medium and various boundary conditions on torsional buckling loads of functionally graded (FG) porous truncated conical panel reinforced by GPLs have been presented. The main purpose of this research is obtaining the best distribution of porosity and GPLs pattern and investigating the influence of adding nano particles on the torsional buckling forces of the shell. Results denote that employing GPL-X pattern in conjunction with porosity distribution 1 provides the maximum value of buckling loads. Besides by adding the nano particles, the amount of buckling loads will increase 100%.

Numerical Investigation on the Impact of Linear Variation of Positive Electrode Porosity upon the Performance of Lithium-Ion Batteries

The diffusion process of lithium-ions in the positive electrode solid phase as within the liquid phase is one of the pivotal factors in determining the battery performance. The effective conductivity and diffusion coefficient of the solid and liquid phases can be regulated by changing the distribution of the volume fraction of active material and porosity on the positive electrode. These crucial parameters can affect the transfer of lithium-ions in the solid and liquid phases and ultimately affect the battery’s performance. In this paper, a pseudo-three-dimensional (P3D) electrochemical-thermal-mechanical (ETM) coupling model is employed to study the non-uniform porosity of the positive electrode, especially the effect of porosity variation on the battery temperature and stress during the discharge process. Through numerical results, we find that reasonable porosity distribution can make the electrode lithiation more uniform and reduce the battery surface temperature by decreasing ionic ohmic heat. In addition, we display the stress distribution on the electrode and inside the active particles after adopting the linear porosity. The results are helpful for an in-depth understanding of the effect of the non-uniform porosity of the positive electrode on the lithium transport mechanism, the stress mechanism, and the thermal mechanism during the operation of lithium-ion batteries (LIBs).

Micro-defect characterization and growth mechanism of plasma electrolytic oxidation coating on 6082-T6 alloy

This work reports micro-defects and growth mechanism of the plasma electrolytic oxidation (PEO) coating formed on the surface of 6082-T6 aluminum alloy. Scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray computed tomography techniques were used to characterize the morphology, phase, microstructure, and porosity of the PEO coating, respectively. The results confirmed a porous outer layer and a dense inner layer in the coating. The PEO coating was composed of γ- and α-Al2O3 phases, and amorphous phases. A layer with only amorphous structures was found near the coating/substrate (C/S) interface, which could be ascribed to the high concentration of P element in the electrolyte. Micro-defects with different sizes and shapes inside the coating were successfully characterized by the high-resolution X-ray computed tomography technique, and the volume reconstruction result revealed a porosity fraction of 5.43% for the coating. A growth model was complemented to explain the growth mechanism and interconnected micro-defects of the PEO coating.

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.

Microstructure and hardness of laser remelted surfaces of Al-5%Cu and Al-4%Cu-1%Ni alloys

Al-based alloys are potential candidates for advanced rapid solidification processes, such as Laser Surface Remelting (LSR) and Additive Manufacturing (AM). However, currently few alloy candidates have emerged for use such as AlSi12 eutectic and AlSi10Mg. This occurs because other alloys are more susceptible to the formation of defects such as porosity, cracks and distortions, which impair high-performance applications. The addition of Ni in Al-Cu alloys is expected to improve the mechanical properties at high temperatures and favors the reduction of the solidification interval, which may decrease the fraction of solidification cracking and porosity. Given the context, the present work investigates the microstructural changes and hardness of Al-5 wt%Cu and Al-4 wt%Cu-1 wt%Ni alloys processed either by centrifugal casting or LSR. By varying laser beam speed and laser average power, a total of 4 combinations for each alloy was accomplished. The CALPHAD computations with 1%Ni alloying revealed a solidification interval reduction of approximately 30%, without reducing the total intermetallics fraction if compared to the binary Al-5%Cu alloy. The microstructure of the rapidly solidified Al-Cu-Ni samples was characterized by a dendritic α-Al matrix, surrounded by a α-Al+Al2Cu+Al7Cu4Ni constituent. A growth transition from epitaxial (bottom) to elliptical/globular (center) was observed in the molten pools with a significant cell spacing reduction from 7.5 µm (as-cast) to 0.6 µm (LSR), which favors an increase in Vickers hardness of approximately 85% if compared to the as-cast samples. The molten pool of the ternary alloy reached a higher hardness of 120 HV as a result of both AlCu and AlCuNi intermetallics acting mutually to strengthen the α-Al matrix.

Investigation of the effects of porosity and volume fraction on the atomic behavior of cancer cells and microvascular cells of 3DN5 and 5OTF macromolecular structures during hematogenous metastasis using the molecular dynamics method

Background and objectiveThe molecular dynamics (MD) simulation is a powerful tool for researching how cancer patients are treated. The efficiency of many factors may be predicted using this approach in great detail and with atomic accuracy. MethodsThe MD simulation method was used to investigate the impact of porosity and the number of cancer cells on the atomic behavior of cancer cells during the hematogenous spread. In order to examine the stability of simulated structures, temperature and potential energy (PE) values are used. To evaluate how cell structure has changed, physical parameters such as gyration radius, interaction force, and interaction energy are also used. ResultsThe findings demonstrate that the samples' gyration radius, interaction energy, and interaction force rose from 41.33 Å, −551.38 kcal/mol, and −207.10 kcal/mol Å to 49.49, −535.94 kcal/mol, and −190.05 kcal/mol Å, respectively, when the porosity grew from 0% to 5%. Also, the interaction energy and force in the samples fell from −551.38 kcal/mol and −207.10 kcal/mol to −588.03 kcal/mol and −237.81 kcal/mol Å, and the amount of gyration radius reduced from 41.33 to 37.14 Å as the number of cancer cells rose from 1 to 5 molecules. The strength and stability of the simulated samples will improve when the radius of gyration is decreased. ConclusionsTherefore, high accumulation of cancer cells will make them resistant to atomic collapse. It is expected that the results of this simulation should be used to optimize cancer treatment processes further.

Vibration analysis of functionally graded porous nano-beams: A comparison study

Porous nano-beams has been widely used in macro as well as nano and micro-sized systems and devices such as biosensors, nano actuators, and nano-electro-mechanical systems. Presence of porosity in the nano-beams significantly affects the material properties and consequently the structural behavior of the nano-beams. Hence it is very important to take care of porosity effects during the modelling of nanostructures. In the present article, vibration characteristics of porous nano beams has been studied along with a comparative study between the two porosity models by taking the cosine type porosity distribution. One porosity model is based on the incorporation of porosity by reducing the average material properties of the constituents in the same amount. While second model is based on the open cell type porosity theory. The effective material properties of the nanobeams are obtained by modifying the power law model according to the different methods of porosity incorporation. The Reddy’s beam theory in conjunction with Eringen’s nonlocal elasticity theory is used to define the displacement field by taking care of size effects. Further, governing equations are derived using the Lagrange’s equation. Finite element method by considering the three noded beam element with four degrees of freedom at each node is used to solve the governing equation. In addition, the influence of porosity co-efficient, the porosity incorporation techniques, and power law index on the effective material properties and vibration characteristics of the functionally graded nano-beams has been studied. A significant influence of porosity incorporation technique on the effective material properties and non-dimensional fundamental frequency of nanobeams has been found for higher values of porosity fraction. For 20% volume of porosity, maximum 6.68% difference between the frequency is found for the considered power law index by using different porosity incorporation methods. While this difference is found 35.74% for 80% volume of porosity with the considered power law index.

Fabrication of foam concrete by use of novel foam generator — vortex jet apparatus: study of foam concrete properties

A new method of foam concrete production by use of vortex jet apparatus (VJA) is studied. The foam produced by VJA exhibits high stability and narrow size distribution of the bubbles’ diameter and the latter correlates well with diameters of foam concrete pores. VJA is a compact device allowing to generate foam without compressor, inhausting the air from the ambience resulting from vacuum in the center of vortex flow. Owing to additional opportunities (compared e.g. with usual axial ejector) like ability to suck the air, longer residence time and higher kinetic energy transformed further into dispersion of the bubbles new device lets to control the parameters of the foam and the density of the foam concrete, thus allowing to create foam with smaller diameter of the bubbles and higher stability. A mechanism of large pores isolation during water absorption tests was proposed. Main properties of foam concrete produced in this study: real and apparent densities, open and total porosities, thermal conductivity and thermal capacity, water absorption, compressive and flexural strengths have been measured; their values fully meet the requirements of Russian and French standards. The main part of pores was attributed to the open porosity because of very close values of total and open porosities. Equations characterizing relative mass of water absorbed by the foam concrete and the fraction of open porosity filled with the water were found as functions of apparent density. It was found that foam concrete production with wide range of densities (from approx. 480 till 1640 kg/m3) is easily attainable by means of VJA. Hence, the VJA could be used as an effective tool for foam generation and foam concrete production.

On the relationship of morphology evolution and thermal conductivity of flax reinforced polypropylene laminates

This paper focuses on the morphology evolution in the forming process of unidirectional flax reinforced polypropylene composite laminates. The link between the morphology evolution and thermal conductivity during consolidation stages is investigated. Hot press forming allows to manufacture several composite laminates at different consolidation stages as a function of the compaction thickness. Microscopic evolution of the laminates in terms of morphology and porosity fractions are evaluated by scanning electron microscopy and X-ray microtomography (µ-CT). Hot disk technique is applied to measure the thermal conductivity of the laminates in in-plane and transverse directions. It is found that the in-plane thermal conductivity almost linearly increases with the reduction of porosity fraction. However, the transverse thermal conductivity remained constant. Beside the proposed relations, a theoretical model, based on a two-level Mori-Tanaka homogenization method is proposed. Considering the three-phases material (i.e., porosity, fiber, and polymer matrix), there is a good agreement between the experiment data and model predictions, but limited predictivity for porosity level above 15% certainly due to simplifying assumptions used in the predictive model.

The relationship between electric processing condition and microstructure in the solidification of multicomponent oxides

Systematic characterization for the relationship between the electropulse processing conditions and microstructure has been carried out in the present work. It is found that electropulse can refine porosity and alter grain morphology considerably. A processing with optimum electropulsing parameters can reduce over 75% volume fraction of porosity and more than 70% average pore diameter in comparison with that of reference sample without electric treatment. Electric current treatment promotes the growth of dendrites with smaller thickness of primary arms dendrite and prevents the liquid entrapping between the growing solid grains. The former is caused by the effect of electricity-enhanced kinetic mobility on the radius of curvature at the tip of dendrite. The latter is attributed to the effects of electric thermodynamics on the microstructural formation such as the enhanced connectivity of conductive phase. The microstructures obtained by electropulsing treatment are favourable for heat conduction, structural strength and crack prohibition. However, the excess pulse frequency and pulse width can generate unwanted heat to counteract electric effect. The research reveals the relationship between electric processing conditions and microstructure in a perfectly controversial solidification condition in oxide materials to that of the metals and alloys. The results confirm from the opposite side the validity of the pulsated solidification.