Porosity Of Samples Research Articles

Preparation and properties of in situ TiC/corundum–mullite electrically conductive ceramic

AbstractIn situ TiC/corundum–mullite electrically conductive ceramics were prepared by carbon‐bed sintering method using bauxite, clay and Ti3SiC2 powders as raw materials. The phase composition, microstructure, shrinkage, apparent porosity, bulk density, compressive strength, and resistivity of samples were investigated. The X‐ray diffraction results indicate that the TiC is completely generated by desilicidation reaction of the Ti3SiC2 at 1 300°C. When the sintering temperature is 1 300°C and Ti3SiC2 powder addition is 22 wt.%, the properties of the sample are optimum, with a longitudinal shrinkage of 2.04%, a radial shrinkage of 2.56%, an apparent porosity of 19.01%, a bulk density of 2.53 g/cm3, a compressive strength of 181 MPa, and a resistivity of 267 Ω·cm. The electrically conductive phase TiC is connected into a complete electrically conductive network. The shrinkages of samples decrease with increasing sintering temperature, which indicates that the samples expand due to secondary mullitization. The continuous electrically conductive network of TiC is destroyed. As the Ti3SiC2 powder addition increases from 14 to 20 wt.%, the resistivity of the samples decreases significantly, but the further increase in the Ti3SiC2 powder addition has no significant effect on the resistivity.

Compositional Differences in Construction and Demolition Wastes (CDWs) for Geopolymer Mortars: A Comparative Study Using Different Precursors and Alkaline Reagents

In the view of the recycling and upscaling processes of waste materials, three different precursors, namely metakaolin, fly ash and volcanic ash, were mixed with Na- or K-silicate to produce binders aimed for the synthesis of geopolymer mortars based on construction and demolition wastes (CDWs). These later, used as aggregates in amount of 50 wt.%, were sampled in two geologically different Italian areas. A comparative study was carried out through a multidisciplinary approach using mineralogical–chemical analyses and physical–mechanical tests for the characterization of six binders and twelve mortars. The aim was to verify the effects of CDW interactions on binders as well as the extent of their compositional influences on the final properties. The chemical and mineralogical results evidenced strong compositional differences among the CDWs, differently influencing the physical–mechanical performances (i.e., compressive strength, density, water absorption and porosity) of the mortar samples. Regardless of the types of precursors and CDWs used, a better influence of K-silicate than sodium on the synthetised samples was observed. Furthermore, the higher versatility of metakaolin mortars with any type of CDW used was noted. Contrary, fly ash and volcanic ash mortars showed better properties with CDWs based on their high silica content and volcanic minerals. The study highlighted the critical roles of the CDW composition and precursor selection in mortar production. It confirmed that CDWs can be recycled for geopolymeric synthesis through proper characterisation and binder selection. Optimising these parameters allows for the successful integration of CDWs into geopolymeric materials. This process supports the advancement of a circular economy in the construction industry.

Towards the hydrogen pore in additively manufactured AlMgScZr alloy: Influencing factors, formation kinetics mechanism

Hydrogen pores in laser additive manufacturing (LAM) aluminum alloys have long been a major challenge for its application. In this study, the formation mechanisms of hydrogen pores and its kinetic behaviors were systematically investigated in laser directed energy deposited (L-DED) AlMgScZr alloy. The results indicated that hydrogen pores accumulated layer by layer at the melt pool boundaries, due to the high nucleation rate and insufficient time to escape of hydrogen pores at the melt pool boundaries. Dring the AlMgScZr powder at 150 °C/4 h enabled the significant decrease of moisture content from 0.0520 wt% to 0.0096 wt%, while the porosity of the L-DED sample only decreased from 0.51% to 0.36%. The increase of laser power decreased the porosity of L-DED sample. Except the L-DED parameters, the alloy composition exerted a more significant influence on hydrogen porosity. When the Mg content increased from 9 wt% to 14 wt%, the porosity exhibited an increase from 0.36 % to 0.52 %. Conversely, the incorporation and subsequent augmentation of Si content resulted in a significant reduction in porosity, reaching as low as 0.15% with an increase to 2 wt%. The solubility and diffusion coefficient of [H] in Al-Mg-Sc-Zr melt with different Mg and Si contents were calculated by density functional theory (DFT). It was observed that increasing the Si content led to a decrease in the nucleation zone for hydrogen pores and reduced porosity. A comprehensive porosity inhibition strategy that combines powder drying, process optimization, and composition regulation have been developed.

Formation of Conductive Networks in Polysulfone Filled with Graphite-Derived Materials

Composites based on polysulfone materials filled with various types of graphite and carbon black were studied and a solution technique was used to create composite materials with filling degrees ranging from 30 to 70% by weight. High filling levels with graphite fillers enabled thermal conductivity of 17.4 W/m·K to be achieved. The addition of carbon black as a filler to the composite helped to improve its mechanical characteristics, and its influence on electrical and thermal conductivity has also been explored. Natural graphite provides the best effect on composite thermal and electrical properties, whereas using artificial graphite allows to improve the mechanical behavior of composites. The relationship between sample density, porosity, and composition, as well as the effect of these factors on composite conductivity, has been studied and addressed.

Study on the Mechanical Degradation and Destruction Characteristics of Coal Oxidation

ABSTRACT Deep coal bodies are often in high stress and high temperature environments. To study the effects of stress and temperature on the mechanical degradation and failure characteristics of coal samples, nuclear magnetic resonance experiments were carried out before and after coal sample oxidation to analyze the effect of oxidation on the porosity of the coal samples. Through mechanical property experiments, the changes in the mechanical properties of the coal samples at different oxidation temperatures is analyzed. Then coal samples of different particle sizes are screened and statistically analyzed to determine the relationship between the fractal dimension of the broken block size and the oxidation temperature. A stress model for the oxidized coal samples is established to analyze its mechanical degradation and its breaking mechanism. Based on the results, As the oxidation temperature increases, The total porosity of the coal samples show an overall increasing trend, the elastic modulus, secant modulus, Poisson’s ratio, and shear modulus show a downward trend, and the destructive strain energy density decreases from 43.33 kg•m−3 to 15.47 kg•m−3, indicating the oxidized coal sample increases in plasticity and decreases in stiffness, resulting in a decrease in the amount of load the sample can carry. The fractal dimensions of the broken block size from raw coal to 200°C coal samples are 2.008, 2.092, 2.150, 2.159, 2.175, 2.183, 2.314, and 2.328. Oxidation leads to the formation a network of tiny fractures inside the coal samples; thus, the broken block size becomes more complex with worsened integrity. A model for the ability of the oxidized coal samples to resist destruction is established, and the diameters of unoxidized areas in oxidized coal samples are calculated to be 45.053, 44.956, 43.031, 41.931, 37.442, 28.081 and 13.778 mm. An analysis of the breaking mechanism of oxidized coal samples was carried out. Our results are beneficial for the safe operation of deep coal seam mining.

Peridynamic simulation of fatigue crack growth in porous materials

Pores are a key type of concerns in additive manufacturing technology. They can significantly affect materials’ fatigue resistance and fatigue crack growth in the structures. In this paper, an intermediately-homogenized (IH) peridynamic (PD) fatigue crack model is introduced for simulating the fatigue crack growth in porous materials. The effect of micro-scale heterogeneity on fatigue failure is preserved in the IH-PD model, where stochastically-generated pre-damage matches materials’ porosity. The PD J-integral, a key parameter used to connect the fatigue simulation and the experimental measurements, is calculated under different porosities, and the independence of PD J-integral on its integration path is verified. Then, the PD fatigue crack model combined with the IH-PD material model is applied to study the dependence of the crack path and growth rate on porosity in compact tension alloy samples. The normalized fatigue life between experimental measurements and numerical results is compared. The normalized fatigue life-porosity relationship calculated from the IH-PD fatigue model matches the average trend of the experimental measurements.

Experimental Study of the Injectability of Infiltration Grouting in Surface Moraine of Pulang Copper Mine

In order to effectively reduce the risk of underground debris flow, surface moraine is solidified and modified by using grouting technology to realize the change in fine-grained moraine from “powder” to “block” to change the source conditions of underground debris flow and to reduce the risk of moraine from the root. In this paper, the effects of grouting pressure, porosity, and pore diameter on the spillability of moraine are investigated experimentally. The results show that the grouting depth increases linearly with increasing sample porosity. For the same sample density, the grouting pressure is proportional to the grouting depth. As the pore diameter of the sample increases, the longitudinal grouting depth of the sample increases, but the transverse diffusion distance decreases. The chemical grout in the moraine is mainly split-infiltration grouting mode. The present research results can provide effective support for the prevention and control of underground debris flow in Pulang Copper Mine.

Experimental Study on the Morphology of Snow Crystal Particles and Its Influence on Compacted Snow Hardness

In their natural state, snow crystals are influenced by the atmosphere during formation and multiple factors after landing, resulting in varying particle sizes and unstable particle morphologies that are challenging to quantify. The current research mainly focuses on the relationship between the porosity of compacted snow samples or qualitatively describes snow crystals and their macroscopic physical properties, ignoring that the significant differences in the morphology of snow crystals also affect their physical properties. To quantitatively evaluate the morphology of snow crystals, we employed optical microscopy to obtain digital images of snow crystals in Harbin, utilizing the Sobel and Otsu algorithms to determine the equivalent particle size and fractal dimension of individual snow particles. In addition, the hardness of snow with a density of 0.4 g/cm3 was measured through a penetration test, with an analysis of its correlation relative to particle size and fractal dimension. The results indicated the fractal dimension as an effective parameter for characterizing particle shape, which decreased rapidly over time and then fluctuated within the range of 1.10 to 1.15. During the initial period, natural snow crystals broke down rapidly, leading to an increase in the percentage of natural snow crystals with an equivalent particle size of 0.2–0.4 mm up to 51.86%. After three days, the sintering effect between snow crystals was enhanced, resulting in an even distribution of the equivalent particle size. Finally, multiple linear regression analysis showed a positive correlation between compacted snow hardness and fractal dimension, with a negative correlation between compacted snow hardness and equivalent particle size. These findings offer valuable technical support and data reference for exploring the relationship between snow’s mechanical properties and its microscopic particle shape.

Defect detection by multi-axis infrared process monitoring of laser beam directed energy deposition

Laser beam directed energy deposition (DED-LB) is an attractive additive manufacturing technique to produce versatile and complex 3D structures on demand, apply a cladding, or repair local defects. However, the quality of manufactured parts is difficult to assess by inspection prior to completion, and parts must be extensively inspected post-production to ensure conformance. Consequently, critical defects occurring during the build go undetected. In this work, a new monitoring system combining three infrared cameras along different optical axes capable of monitoring melt pool geometry and vertical displacement throughout deposition is reported. By combining multiple sensor data, an automated algorithm is developed which is capable of identifying the formation of structural features and defects. An intersecting, thin-walled geometry is used to demonstrate the capability of the system to detect process-induced porosity in samples with narrow intersection angles, which is validated using micro-CT observations. The recorded results indicate the root cause of this process-induced porosity at the intersection, and it is shown that advanced toolpath planning can eliminate such defects. The presented methodology demonstrates the value of multi-axis monitoring for identifying both defects and structural features, providing an advancement towards automated detection and alert systems in DED-LB.

Size-controlled synthesis of La and chitosan doped cobalt selenide nanostructures for catalytic and antibacterial activity with molecular docking analysis

Co-precipitation method was adopted to synthesize ternary heterostructure catalysts La/CS-CoSe NSs (lanthanum/chitosan‑cobalt selenide nanostructures) without the use of a surfactant. During synthesis, a fixed amount (3 wt%) of CS was doped with 2 and 4 wt% La to control the growth, recombination rate and stability of CoSe NSs. The doped samples served to enhance the surface area, porosity and active sites for catalytic degradation of rhodamine B dye and antibacterial potential against Staphylococcus aureus (S. aureus). Additionally, the synthesized catalysts were examined for morphological, structural and optical characteristics to assess the influence of dopants to CoSe. XRD spectra verified the hexagonal and cubic structure of CoSe, whereas the porosity of the undoped sample (CoSe) increased from 45 to 60 % upon incorporation of dopants (La and Cs). Among the samples analyzed during this study, 4 % La/CS-CoSe exhibited significant bactericidal behavior as well as the highest catalytic reduction of rhodamine B dye in a neutral environment. Molecular docking analysis was employed to elucidate the underlying mechanism behind the bactericidal activity exhibited by CS-CoSe and La/CS-CoSe NSs against DHFRS. aureus and DNA gyraseS. aureus.

Effect of heat treatment on microstructure and mechanical properties of AlSi10Mg fabricated using laser powder bed fusion

Thermal heat treatment is an important step in many metal additive manufacturing processes, particularly laser powder bed fusion (PBF-LB), as it can homogenize the microstructure and enhance the properties of the resulting parts. The effects of post-processing via direct ageing (DA), stress-relieving (SR), and DA or SA followed by annealing or hot isostatic pressing (HIP), on the microstructure, porosity, and resultant mechanical properties of AlSi10Mg samples manufactured using PBF-LB were investigated in this study. Samples were fabricated over a range of processing conditions to probe different starting microstructures and pore features. Porosity and sub-grain solidification cells were characterized because these features are known to influence strength, ductility, and microhardness. DA increased strength at the expense of ductility due to the precipitation of Si-rich particles while SR improved ductility at the expense of strength due to the broken Al/Si eutectic microstructure. Subsequent annealing of DA samples resulted in further breakdown of the Al/Si eutectic microstructure as well as coarsening of Si-rich precipitates, resulting in lower strength and higher ductility than DA alone. HIP resulted in near fully dense and homogenized samples with coarse Si particles, significantly increasing elongation over all other heat treatments. This study shows that processing parameters and heat treatments can be used to tailor porosity, cell size, and resultant mechanical properties of PBF-LB AlSi10Mg.

Investigating surface integrity and mechanical behavior of selective laser melting for dental implants

AbstractSelective laser melting (SLM) is a contemporary manufacturing method that offers numerous advantages for producing various components. This research focuses on the examination of a dental implant sample fabricated using the SLM method. The investigation encompasses multiple aspects, including hardness, dimensional accuracy, strength, and surface properties. The results demonstrate that the hardness of the SLM sample is comparable to that of machined samples, establishing it as a viable alternative to traditional production methods. Dimensional tests reveal that the SLM sample adheres to the required acceptance limits for critical dimensions. The strength of the sample, with a value of 700 MPa, proves to be acceptable for medical applications. The presence of surface porosity and holes in the SLM sample highlights its potential for enhanced bone ossification. However, challenges associated with thread construction in the SLM process require further attention. Overall, this research showcases the promising aspects of the SLM method for dental implant production, while also identifying areas for future investigation and improvement.

Experimental Research on the Permeability of Granite Under Different Temperature Cycles

In this paper, through the permeability test of granite under different temperature cycles, the change law of porosity and permeability of rock samples after different temperature cycles was studied, and the relationship between the P-wave velocity and porosity and permeability was established by regression analysis. The results show that the porosity and permeability of the granite samples decreased significantly in one to three high-temperature cycles, showing a logarithmic change, and with the increase of the number of cycles, the decreasing rate gradually decreased after five to 10 thermal cycles, which is beneficial to the long-term development of deep geothermal resources. Under thermal cycles at different temperatures, the P-wave velocity of granite has a logarithmic correlation with permeability and porosity. As the number of cycles increases, the relationship between permeability, porosity, and P-wave velocity changes from a logarithmic relationship between one to three cycles to a linear relationship between five to 10 cycles. After thermal cycle treatment at different temperatures, there is an excellent logarithmic relationship between the P-wave velocity and porosity and permeability, and it has a high correlation. The porosity and permeability of granite can be estimated nondestructively by measuring the wave velocity. Using a scanning electron microscope (SEM) to observe the granite at 450℃, trivial particles appeared between the pore structure, and the internal structure of the rock sample was destroyed under the action of the thermal cycle. The change mechanism of physical property deterioration in deep geothermal energy mining is revealed, guiding deep geothermal energy mining.

The influence of hydrocarbon generation on the sealing capability of mudstone caprock rich in organic matter

To investigate the sealing capability of mudstone caprock during the evolution of organic matter (OM)-rich mudstone, a series of hydrous pyrolysis experiments were first conducted to examine the impact of hydrocarbon generation. The pore type, pore structure, porosity, and gas breakthrough pressure of pyrolytic residual samples were analyzed by field emission scanning electron microscopy, low pressure nitrogen adsorption measurements, porosimetry, and gas breakout core experiments. To model the environment at different depths, these six experiments on hydrous pyrolysis were performed at different temperatures, lithostatic pressures, and hydrodynamic pressures, while other experimental factors such as the original sample, heating time, and rate were kept constant. The results showed that during the thermal evolution process, hydrocarbons were generated from OM in mudstone, resulting in the formation of pores within the OM. Organic acids produced by hydrocarbon generation effectively dissolved minerals, leading to the creation of numerous dissolution pores. Changes in pore type led to changes in pore structure and porosity. The volume of micropores and macropores showed an increasing trend before reaching a Ro value of 1.41%. However, after passing this threshold, they began to decrease. The volume of mesopores showed a decreasing trend before reaching a Ro value of 1.32%. After 1.32%, they began to increase. The porosity was mainly affected by the pore volumes of the mesopores and macropores. The porosity exhibited two peaks: the first occurred at a Ro value of 0.72%, with a porosity level of 4.6%. The second occurred at a Ro value of 1.41% and a porosity level of 10.3%. The breakthrough pressure was a comprehensive reflection of these influences, and its trend exhibited a negative correlation with porosity (R2 = 0.886). For two high values of porosity, the breakthrough pressure corresponded to two low values. Smaller values of the breakthrough pressure indicated a poorer sealing capability of the mudstone caprock. Overall, hydrocarbon generation in the mudstone affected the sealing capability. The mudstone in the studied area exhibited good sealing at Ro below 1.32%. However, once above the 1.32% threshold, the fluctuations of the breakthrough pressure values exhibited considerable variability, requiring a comprehensive evaluation to assess its sealing capability.

Regulating the pore structure of periclase refractories by adding Y2O3 to enhance corrosion resistance for copper slag

AbstractThe penetration of copper‐smelting slag into refractories is a major challenge to the research of chromium‐free refractories for copper‐smelting furnace. In this paper, Y2O3 was added to regulate the pore structure of periclase refractories, which enhanced their various properties, especially corrosion resistance to copper converter slag. The results showed that the periclase refractories doped with 1.0 wt.% Y2O3 (1Y sample) possessed the optimum properties. Compared to the sample without Y2O3, the apparent porosity of 1Y sample was decreased by 7.3%, and its average pore diameter was only 3.7 μm. The addition of Y2O3 filled the pores among MgO grains and promoted the expansion of high melting point silicates, thereby reducing the pore size and causing more complex pore structures. This was beneficial to improving the corrosion resistance of periclase to copper slag, especially to prevent the penetration of Cux+ and Na+. After static slag corrosion, the permeability index was significantly decreased by 41% compared to periclase refractories without Y2O3. Moreover, compared to industrial MgO–Cr2O3 refractories, the 1Y sample possessed better resistance to copper slag erosion based on rotating finger tests, and its permeability index and penetration depth decreased by almost 50%.

Pore structure exponent of Archie's law in a dual-porosity medium: Vuggy reservoirs

The porosity exponent (m) is one of the most critical parameters of Archie's equation and plays a significant role in quantitative evaluation of petroleum reservoirs. In vuggy carbonate reservoirs, it is difficult to separately quantify the matrix pores and vugs in natural core samples; consequently, how the matrix pores and vugs influence m remains unclear. In this study, a novel method was developed for preparing artificial vuggy core samples with specific values for matrix and vug porosity. The optimal preparing parameters of vuggy core samples, for the material to be consistent with the porosity and permeability of actual core samples, were as follows: 0.25 mm dolomite particles and 0.18 mm glass beads as the rock skeleton, epoxy resin as the binder, 10 mm sodium thiosulfate to form the vugs (compacted and gasified), a component ratio of 1:3:3, and a compaction pressure of 20 MPa. Next, petrophysical and resistivity experiments were carried out to obtain the m and porosity value of 15 artificial vuggy cores. Based on a comprehensive analysis of the artificial core samples, actual core samples, and porosity model, the response of m to matrix and vug porosity was modeled further. The key results are as follows: (1) the larger the portion of vugs to total porosity (Φv/Φ), the greater the increase in m with a range from 2 to 3.5 was found; (2) with the increases of Φ, m increases first and then decreases, where the inflection point of artificial and actual samples is in the range of Φ≈ 18%–20%; (3) the trend of variation of m with Φ is mainly controlled by Φv/Φ or Φm/Φ rather than Φv or Φm individually. What was revealed in this study, can provide theoretical support for using Archie's equation in carbonate reservoirs.

Estimation of pore structure and permeability in tight carbonate reservoir based on machine learning (ML) algorithm using SEM images of Jaisalmer sub-basin, India

Analyzing the pore structure in carbonate reservoirs plays a crucial role in predicting fluid flow characteristics within these formations. The goal of the study was to use machine learning techniques for pore structure analysis and estimation of permeability in carbonate reservoirs. We implemented these algorithms by examining 2D scanning electron microscope (SEM) images of carbonate samples from the Jaisalmer sub-basin captured at various magnifications. In the initial stage of the analysis, various binarization algorithms were applied to determine carbonate sample porosity. Among these algorithms, the MaxEntropy algorithm gave a porosity value closely aligned with those obtained through petrography analysis. We employed the watershed algorithm to find the pore network parameters of carbonate samples at various magnifications. We observed that changes in magnification affected pore network parameters, resulting in a reduction in pore size distribution, throat radius, and grain size. Subsequently, we employed the numerical lattice Boltzmann method (LBM) to estimate the permeability of carbonate samples and compared to values derived from well logs. We employed machine learning (ML) algorithms, specifically Artificial Neural Network (ANN) and Support Vector Machine (SVM), to predict the permeability of carbonate samples. The input features for these models were the pore network parameters, while the LBM permeability values served as the output. We examine the prediction performance of these methods against the measured LBM permeability by conducting the error analysis and the coefficient of determination (R2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${R}^{2}$$\\end{document}) calculation. Our findings revealed that the ANN models outperformed the SVM models. Specifically, the ANN model displayed an impressive R2 value of 0.892, along with root mean square error (RMSE), mean squared error (MSE) and, mean absolute error (MAE) values of 1.927, 3.716 and 1.580, respectively. In contrast, the SVM model yielded an R2 value of 0.849, with RMSE, MSE and, MAE values of 2.324, 5.401 and, 2.166 respectively, when assessed on testing data of measured permeability. This study found that ANN is more dependable, robust, and precise than SVM in forecasting carbonate sample permeability.

Experimental Study on Compaction Deformation and Gas Permeability Properties for Crushed Limestone.

The mining goaf is enriched in coalbed methane (CBM) resources, and it is imperative to realize its efficient extraction. The gas permeability properties of the crushed coal and rock in the caved zone of mining goaf are the basis for the study of its internal CBM migration and enrichment law. In this study, the compaction deformation and gas permeability properties of crushed limestone with different particle sizes were revealed. The results show that (1) the deformation resistance capacity of the crushed limestone increased with increasing stress. The decreasing trend of porosity of samples with different particle sizes in the early and later compression periods is significantly different. Particle RR of the lower layer is smaller than that of the other layers. (2) The permeability of the sample decreases with decreasing porosity and nitrogen pressure, and it is between 10-12 and 10-10 m2. Nitrogen migration within the crushed limestone requires the pseudo-threshold pressure gradient, which ranges from 64.86 to 311.42 Pa/m. (3) The average permeability growth amplitude of the sample shows a logarithmic decreasing trend with the decrease of porosity. The average permeability growth amplitude of the 5-10 mm sample at the same porosity was 15.9-22.3 times that of the 0.315-0.63 mm sample. (4) The permeability of crushed limestone on both sides of the lower layer in the caved zone is much larger than that of other locations. The results are of great practical significance for accurately predicting the CBM enrichment area of mining goaf and then selecting the final position of the extraction drilling hole.

The effect of tensile deformation of knitted fabrics on their electromagnetic shielding ability, electrical resistance, and porosity

Nowadays, electrically conductive textile materials are widely used also for sensing applications in addition to being used as antistatic, electromagnetic shielding, for creating smart textiles, etc. The main aim of this paper is to study the effect of tensile deformation applied on knitted fabrics on their electromagnetic shielding ability, electrical resistance, and porosity to gain knowledge for the construction of textile-based wireless strain sensors. For the experiment, silver-coated yarn was chosen to produce knitted fabrics with two different patterns and three levels of stitch densities. The uniaxial and biaxial deformation was applied to samples and at the same time, the change of electromagnetic shielding ability, electric resistance, and porosity of the sample set was evaluated. It can be summarized, that the vertical stretch has the highest positive effect on the electromagnetic shielding ability and the maximum shielding sensitivity is 12 % compared to other deformation types. In general, the electrical resistance decreases during increased stretch due to the increasing number of contacts between electrically conductive yarns, which causes a decrease in the contact resistance and also a decrease in total electrical resistance. The highest positive effect on the porosity of samples represents biaxial deformation. The finding that the overall shielding efficiency is positively influenced by the electrical conductivity of the sample and at the same time negatively influenced by the increasing porosity during tensile deformation was the motivation to construct a simple regression model for the prediction of the electromagnetic shielding ability of the sample during its extension.

Effect of fibre orientation on the mechanical response of reinforced sand, detected with x-ray tomography

The mechanical behaviour of fibre-reinforced sands (FRS) has been thoroughly explored with a laboratory study, firstly investigating the influence of relevant parameters such as grading index, soil density, amount, diameter, and length of fibres then focusing on their orientation with respect to the principal stress directions. This aspect has been deeply investigated performing parallel tests on samples of pure sand and on samples with randomly and uniformly oriented fibres compacted at a similarly high relative density (Dr≈1). Direct and triaxial shear tests have been performed, the former enforcing deformation on a predetermined shear plane. The results show that reinforcement with oriented fibres provides a higher strength and ductility to the sand. The grain scale investigation of the materials’ response to direct shearing has been carried out performing X-ray tomography post-mortem (i.e., after the test). The evolution of porosity in several samples prepared with the same procedure and sheared under the same conditions has been studied freezing the material fabric with nanosilica grout injected at different displacement levels. On the contrary, X-ray tomography performed along with miniature triaxial tests (operando method) enabled the analysis of the spatial distribution of deviatoric strain too. In both cases, maps show the relevant role of fibres orientation with reference to the shear band. If adequately activated, fibres tension modifies the strain field in the samples, preventing the fragile rupture along a shear plane and transferring the stresses to the outer soil portions, in this way providing a more dilatant and ductile overall response of the reinforced material.