Void Distribution Research Articles

Conformal structure of quantum wave mechanics

This work interprets the quantum terms in a Lagrangian, and consequently of the wave equation and momentum tensor, in terms of a modified spacetime metric. Part I interprets the quantum terms in the Lagrangian of a Klein–Gordon field as scalar curvature of conformal dilation covector nm that is proportional to [Formula: see text] times the gradient of wave amplitude R. Part II replaces conformal dilation with a conformal factor [Formula: see text] that defines a modified spacetime metric [Formula: see text]= exp[Formula: see text], where g is the gravitational metric. Quantum terms appear only in metric [Formula: see text] and its metric connection coefficients. Metric [Formula: see text] preserves lengths and angles in classical physics and in the domain of the quantum field itself. [Formula: see text] combines concepts of quantum theory and spacetime geometry in one structure. The conformal factor can be interpreted as the limit of a distribution of inclusions and voids in a lattice that cause the metric to bulge or contract. All components of all free quantum fields satisfy the Klein–Gordon equation, so this interpretation extends to all quantum fields. Measurement operations, and elements of quantum field theory are not considered.

Evaluation of aggregates, fibers and voids distribution in 3D printed concrete

3D printed concrete technology has received a traffic attention in construction industry in recent years, due to the potential advantage: time and labor savings, cost reduction, low environmental impact. In this study, the influence of distribution of aggregate and steel fiber on the mechanical properties of 3 D printed concrete is experimentally investigated. The distribution characteristic of aggregate and steel fiber in 3 D printed concrete are evaluated by using X-ray computed tomography (X-CT) with 2 D image analysis method. The cast concrete is performed as reference. It is found that the aggregate and fiber in cast concrete are relatively evenly distributed and no alignment, while there is an orientation probability of more than 40% for aggregate, and 74% for fiber, respectively, along the printing direction in ± 20° in printed concrete. Meanwhile, using X-CT, the porosity, void sizes, shapes and distributions in printed and cast concrete are also investigated. Furthermore, it is observed that the printed and cast samples comprise of different voids, due to the different construction processes. Finally, the results prove that the performance difference for the printed concrete at different directions possibly depends on the orientation distribution of the aggregate/fiber, as well as the irregular voids, since the aggregates/fibers are orientated by the nozzle along the printing direction.

Effect of steel fiber distribution on the mechanical properties of UHPC caused by vehicle-bridge coupling vibration

With the acceleration of infrastructure construction, the risk of being exposed to vehicle-bridge coupling vibration is getting more common for the unhardened cementitious materials, which also intensifies the stress on the concrete and leads to the presence of micro-cracks at early age. In order to simulate vehicle-bridge coupling vibration in the actual construction sites, the properties and microstructure evolution of ultra-high performance concrete (UHPC) were evaluated systematically by fixing the specimens on an electric vibration table immediately after casting. The vibration parameters considered in this work involve the frequency and the amplitude according to the in-site monitor data. The heterogeneous distribution of air voids and steel fiber was determined by X-CT on cylindrical specimens with diameter of 70 mm and height of 100 mm quantitatively. In the early hydration, the position and distribution of steel fibers in the UHPC matrix could be able to move freely, which has significant impact on the mechanical properties. The compressive strength and drying shrinkage of UHPC specimens gradually increase with increasing the amplitude and frequency. However, a large amplitude and frequency would be detriment to the flexural and tensile strength due to changes in the angle and spatial distribution of steel fiber although the total porosity only varies slightly. Increasing amplitude and frequency promotes the presence of coarser air bubble and reduction of steel fibers inclination angle. This study is helpful for the design and application of UHPC in the actual construction sites, which could avoid the material failure during construction.

The Spatial Distribution of Cellular Voids in the Human Otic Capsule: An Unbiased Quantification of Osteocyte-Depleted Areas.

This study aimed to describe the spatial distribution of osteocyte-depleted areas, so-called cellular voids, in the human otic capsule and compare it with that of otosclerosis. Systematic histological studies of the bony otic capsule have revealed an osteoprotegerin (OPG)-mediated inhibition of normal bone remodeling around the inner ear. The resulting accumulation of bony degeneration and dead osteocytes has been thoroughly documented, and the spatial distribution of dead osteocytes and matrix microcracks resembles that of the human ear disease otosclerosis. Clusters of dead osteocytes that may interfere with osteocyte connectivity and thereby the OPG signaling pathway have been described in human temporal bones. It is possible that these cellular voids create disruptions in the antiresorptive OPG signal that may give rise to local pathological remodeling. Recently, a method of detecting cellular voids was developed. This study uses unbiased stereology to document the spatial distribution of cellular voids in bulk-stained undecalcified human temporal bone. Cellular voids accumulate around the inner ear and increase in number and size with age. Furthermore, cellular voids are more frequently found in the anterior and lateral regions of the otic capsule, which are known predilection sites of otosclerosis. This colocalization of cellular voids and otosclerosis suggests a causal relationship between focal degeneration and otosclerotic remodeling.

Investigating mechanical performance and interface characteristics of cold recycled mixture: Promoting sustainable utilization of reclaimed asphalt pavement

The recycling and sustainable utilization of reclaimed asphalt pavement (RAP) are the key method to improve resource conservation and reduce energy consumption in roadway construction. The cold-recycled technology has been regarded as a promising recycling one because it can achieve mixing at room temperature and high utilization of RAP. Investigating the mechanical mechanism of cold-recycled asphalt mixture (CRAM) is the basis for large-scale application. Thus the splitting tests were carried out to study the influencing law of the material components on the strength performance of CRAM by varying RAP, cement and asphalt content. Then the effects of material component on the strength mechanism were further revealed by the interface characteristics analysis, including void and filler parameters, binder and interface transition zone (ITZ) thickness. The results show that the CRAM with more RAP has a higher splitting strength and the aged asphalt contributes to the reduction of void number around the aggregate interface, indicating a stronger bonding effect with binder. The asphalt mixture has lower void size, void number and porosity than cement mixture, and shows more uniform distribution of binder thickness and lower void distribution difference between the ITZ and the mortar phase, which is conducive to force uniformly and prevent stress concentration within mixture. The above outcomes confirm the effects of strength improvement from RAP and the void increment from cement, and the contents could be reasonably increased for RAP and strictly controlled for cement to ensure strength performance of CRAM while promoting saving energy and environmental protection.

Biaxial buckling analysis of an innovative active sandwich plate

Fragility and the presence of a poisonous substance (lead) are the two major issues with traditional piezoceramics and structures that include them. This work suggests an active structure that is lightweight, flexible, and eco-friendly such that a polymeric foam plate is sandwiched between two piezoelectrically activated nanocomposite layers. A combination of a polymer and piezoelectric nanowires (NWs) of zinc oxide (ZnO) is used in the nanocomposite layers. For the proposed active structure, two types of void distributions and functionally graded (FG) distributions of the NWs have been assumed in each corresponding layer. The buckling characterization of the proposed eco-friendly active sandwich plate (EFASP) under biaxial mechanical loads has been conducted using an extended meshless solution based on a third-order theory. An in-depth parametric study on the EFASPs’ biaxial buckling resistance revealed that increasing NW content considerably enhances buckling resistance, with this enhancement strongly reliant on the distribution profile of the NWs. Moreover, it was observed that embedding voids in the substrate layer can lead to a large structural weight reduction while only marginally lowering the buckling performance of suggested EFASPs.

Probabilistic failure mechanisms via Monte Carlo simulations of complex microstructures

A probabilistic approach to phase-field brittle and ductile fracture with random material and geometric properties is proposed within this work. In the macroscopic failure mechanics, materials properties and spatial quantities (of different phases in the geometrical domain) are assumed to be homogeneous and deterministic. This is unlike the lower scale with strong fluctuation in the material and geometrical properties. Such a response is approximated through some uncertainty in the model problem. The presented contribution is devoted to providing a mathematical framework for modeling uncertainty through stochastic analysis of a microstructure undergoing brittle/ductile failure. Hereby, the proposed model employs various representative volume elements with random distribution of stiff inclusions and voids within the composite structure. We develop an allocating strategy to allocate the heterogeneities and generate the corresponding meshes in two- and three-dimensional cases. Then the Monte Carlo Finite Element Method (MC-FEM) is employed for solving the stochastic PDE-based model and approximate the expectation and the variance of the solution field of brittle/ductile failure by evaluating a large number of samples. For the prediction of failure mechanisms, we rely on the phase-field approach which is a widely adopted framework for modeling and computing the fracture phenomena in solids. Incremental perturbed minimization principles for a class of gradient-type dissipative materials are used to derive the perturbed governing equations. This analysis enables us to study the highly heterogeneous microstructure and monitor the uncertainty in failure mechanics. Several numerical examples are given to examine the efficiency of the proposed method.

Vapor Barrier Properties of Cold Plasma Treated Corn Starch Films

The development and efficient production of effective bioplastics is a hot topic, required to face up to the issue of the difficult disposal of plastics derived from oil. Among the different natural sources of bioplastics, starch is one of the most promising. However, for most applications, the proper mastering of the surface properties of bioplastic is necessary. We report about the surface modification of extruded corn starch films by means of cold plasma based on helium (He) and hexamethyldisiloxane (HMDSO). The differently treated surfaces were functionally characterized in wettability and water absorption. The nanoscale morphology was assessed by scanning electron microscopy and atomic force microscopy. The obtained images were analyzed by advanced figures describing both texture and amplitude parameters, including fractal behavior. The combined treatment (He/HMDSO) resulted in more homogeneous films with smaller, better-distributed grains compared to the case wherein He was not used. Despite the different morphologies observed, starch coated by HMDSO alone and by He/HMDSO presented similar hydrophobic character, with contact angles higher than 110°. Plasma treatment with HMDSO and He/HMDSO resulted in a significant reduction of absorbed water content without reduction of water vapor permeability. The nanotexture of the films did not present statistically significant differences, in terms of spatial complexities, dominant spatial frequencies, homogeneous void distribution, and surface percolation.

Numerical investigation for the suitable choice of bubble diameter correlation for EMMS/bubbling drag model

Mesoscale bubbles exist inherently in bubbling fluidized beds and hence should be considered in the constitutive modeling of the drag force. The energy minimization multiscale bubbling (EMMS/bubbling) drag model takes the effects of mesoscale structures ( i.e ., bubbles) into the modeling of drag coefficient and thus improves the coarse-grid simulation of bubbling and turbulent fluidized beds. However, its dependence on the bubble diameter correlation has not been thoroughly investigated. The hydrodynamic disparity between homogeneous and heterogeneous fluidization is accounted for by the heterogeneity index, H d , which can be affected by choice of bubble diameter correlation. How this choice of bubble diameter correlation influences the model prediction calls for further fundamental research. This article incorporated seven different bubble diameter correlations into EMMS/bubbling drag model and studied their effects on H d . The performance of these correlations has been compared with the correlation used previously by EMMS/bubbling drag model. We found that some of the correlations predicted lower H d by order of a magnitude than the correlation used by the original EMMS/bubbling drag. Based on such analysis, we proposed a modification in the EMMS drag model for bubbling and turbulent fluidized beds. A computational fluid dynamics (CFD) simulation using two-fluid model with the modified EMMS/bubbling drag model was performed for two bubbling and one turbulent fluidized beds. Voidage distribution, time averaged solid concentration and axial solid concentration profiles were studied and compared with the previous version of the EMMS/bubbling drag model and experimental data. We found that the right choice of bubble diameter correlations can significantly improve the results for CFD simulations.

The effects of silanized rubber and nano-SiO2 on microstructure and frost resistance characteristics of concrete using response surface methodology (RSM)

Waste rubber powder can be used to enhance the frost resistance of cement concrete. Conventionally, only the rubber powder is directly mixed into concrete, but its mechanical properties are reduced significantly. However, mixing modified rubber, nanometer materials, lime ash, and cement concrete can improve the frost resistance and compressive strength of concrete at the same time. The main objective of this paper is to evaluate the potentiality of utilizing silanized rubber (SR) powder and nano-SiO2 (NS) to develop frost-resistant concretes. Determination of the frost-resistant effect of concrete mixture incorporated with SR and NS on the pore structure and mechanical characteristics was performed by response surface methodology (RSM). Results of scanning electron microscopy (SEM) tests along with Fourier transform infrared spectroscopy (FT-IR) are reported to evaluate the effect of frost resistance from microstructure. Results of the conducted tests show that the combination of SR and NS has a synergistic effect, which makes the distribution of voids in concrete more uniform, and the damage of mass loss rate and relative dynamic modulus of elastic (RDME) after a freeze–thaw cycle is lower. At the optimum content of designed concrete, there is a high correlation between frost resistance and void structure.

Multi-parametric analysis on buckling of nano-reinforced prepreg wound riser considering void shape and distribution

Buckling resistance of composite riser always demonstrates diverse sensitivity to the fiber, matrix, and defects. The purpose of this paper is to analyze the parametric effect on the buckling load of prepreg wound riser under combined loads considering the process-induced voids. The analytical model of composite riser with void defect is established firstly based on the Flügge model and Galerkin method. The accuracy of the proposed model is verified with previous experimental research in mechanical behavior of composite cylinder. Then, there are five relevant input parameters that are selected such as volume content of carbon nanotubes and void, void shape and distribution, metal liner. Further, based on the proposed model, the multi-parametric analysis on buckling behavior of composite riser is investigated considering process-induced voids. The results imply that the void volume content has a stronger impact on the buckling resistance than carbon nanotubes. Besides, the increment of buckling load of composite riser presents different trends as the void shape evolves from flat ellipse to vertical ellipse. By correlating the prepreg winding process parameters, this study can provide guidance for process designers in exploiting optimal winding parameters for high buckling resistance to weight ratios.

Effects of geometric array and size of internal voids on tensile ductility of AZ31 magnesium alloy sheets

This study aims to investigate the contributions of the geometric array and size distribution of perforated cylindrical voids to the tensile strain of a metallic sheet through the numerical correction of the plastic constraint factor with regard to the geometric array of internal voids. In AZ31 alloy sheets fabricated via strip casting, internal voids were formed via mechanical drilling in the form of perforated cylindrical holes. The tensile strain decreased significantly (from 0.18 to 0.01) as the void area fraction increased to 40%, and its nominal value decreased with an increase in the void size, even when the geometric array (ratio of void size to ligament distance between voids, a/l) was maintained. A plastic constraint factor describing the geometric array and size distribution of perforated cylindrical voids was proposed through the modification of an original form for isolated spherical voids, and the theoretical prediction using a modified constitutive model agreed well with the experimental results. The tensile ductility of a metallic sheet with perforated cylindrical voids depends more sensitively than isolated spherical voids on the variation in the void area fraction, because the effective void area fraction is overestimated by the exclusion of the strain-hardening exponent term in the modified plastic constraint factor. Additionally, increases in the void size and void area fraction at a fixed a/l ratio lead to a reduction in the tensile strain, by the increase of the plastic zone and the intensification of stress concentration around a void.

Eficiência da técnica de encapsulamento em solo argiloso com elevadas concentrações de cloreto de zinco com agentes tradicionais

ABSTRACT Although the encapsulation technique has been used in environmental remediation for over three decades, there are few studies evaluating its efficacy for high contaminant concentrations. Therefore, this study aims to evaluate the encapsulation technique efficiency of clayey soil contaminated with 5% and 10% of zinc chloride, using lime and cement. Chemical, mechanical, mineralogical, and microscopic analyses were performed for pure, contaminated, and encapsulated soil, based on X-ray fluorescence (XRF/EDX), unconfined compression strength (UCS), atomic absorption spectrometry (AAS), scanning electron microscopy/energy dispersive X-ray spectrometer (SEM/EDS), and X-ray micro-computed tomography (micro-CT) tests. Although chemical interactions between zinc and lime negatively affected the gains when compared to cement, both encapsulating agents increased the strength over the curing periods of 7, 28, and 60 days. The leachates presented a significant reduction in the contaminant concentration, above 77% for critical experimental conditions. The contaminant reduced the presence of chemical elements that compose the soil matrix, consequently causing the voids to increase; in contrast, pozzolanic reactions promoted by the addition of lime and cement resulted in homogeneous voids distribution, enhancing the mechanical behavior and the capability of zinc chloride retention.

Strain localization analysis in materials containing randomly distributed voids: Competition between extension and shear failure modes

Strain localization is often a precursor to the ductile failure of materials. This paper investigates plastic strain localization phenomena in the case of random microstructures, namely cubic cells made of an elastic-perfectly plastic matrix embedding distribution of identical non-overlapping spherical voids. The consideration of random microstructures allows for a better representation of the interaction between voids and greater diversity of failure modes than single-void (or unit) cells. The cells are simulated by means of the finite element (FE) method for proportional stress loading paths with controlled stress triaxiality and Lode parameters. Strain localization is detected by Rice’s criterion computed at the cell level. This criterion is shown to accurately capture the onset of localization and the type of failure mode, either extension or shear banding. Moreover, the influence of the loading orientation, i.e. the orientation of the principal axes of the applied stress tensor with respect to the microstructure cube, is systematically studied. Significant anisotropy of failure behavior is observed, especially in the case of single void unit cells, which can be attributed to the intrinsic anisotropy of the simulation cells. Finally minimal failure strain values at localization with respect to all loading orientations are found. A zone of reduced ductility is observed under generalized shear loading conditions.

Study on Damage of the OGFC Mixture Based on Characteristics of Void Distribution

The void distribution characteristics of the drainage asphalt mixture have a certain influence on its durability. In this paper, X-ray CT technology and digital image processing technology are used to study the void distribution characteristics of three different graded asphalt mixtures, and the void ratio, void quantity, void equivalent diameter, and void fractal dimension of drainage asphalt mixtures are determined. On this basis, the damage characteristics of the asphalt mixture are analyzed with the split strength as the index, and the relationship between the void fractal dimension and the split strength is established. The relationship between the void diameter and the durability of the OGFC mixture is determined by the influence of the void diameter on the void fractal dimension. The results show that the void distribution characteristics of the OGFC mixture have a significant impact on its durability. The void larger than 3 mm in OGFC asphalt mixture has a greater impact on the durability of asphalt mixture. Even if the void ratio of different OGFC mixtures is relatively close, its durability is also very different. The difference in durability is mainly due to the difference of the void structure and the proportion of the number of large voids above 5 mm.

A Homogenization Approach for Turbulent Channel Flows over Porous Substrates: Formulation and Implementation of Effective Boundary Conditions

The turbulent flow through a plane channel bounded by a single permeable wall is considered; this is a problem of interest since a carefully chosen distribution of grains and voids in the porous medium can result in skin friction reduction for the flow in the channel. In the homogenization approach followed here, the flow is not resolved in the porous layer, but an effective velocity boundary condition is developed (and later enforced) at a virtual interface between the porous bed and the channel flow. The condition is valid up to order two in terms of a small gauge factor, the ratio of microscopic to macroscopic length scales; it contains slip coefficients, plus surface and bulk permeability coefficients, which arise from the solution of microscale problems solved in a representative elementary volume. Using the effective boundary conditions, free of empirical parameters, direct numerical simulations are then performed in the channel, considering a few different porous substrates. The results, examined in terms of mean values and turbulence statistics, demonstrate the drag-reducing effects of porous substrates with streamwise-preferential alignment of the solid grains.

Effects of Freeze-Thaw Cycles on the Internal Voids Structure of Asphalt Mixtures.

Freeze–thaw cycle is one of the main distresses of asphalt pavement, and the law of freeze–thaw damage has always been an important topic. In this paper, X-ray computed tomography (CT) of asphalt mixture before and after freezing and thawing was carried out, and its two-dimensional (2D) digital image was recognized. Firstly, the eigenvalues of internal voids of asphalt mixture are extracted. Then the distribution of internal voids was analyzed. Finally, the evolution law of internal voids was summarized. The research results show that the characteristic mean value of the 9th cycle is the irreversible limit of freeze–thaw damage, and the non-resilience after the large void area increases is the fundamental reason for the accumulation of freeze–thaw damage. The source of void damage shifts from large voids to small voids, and the middle-stage is a critical stage of freeze–thaw damage. This work quantitatively evaluates the internal freeze–thaw damage process of asphalt mixture, and a morphological theory of the evolution of void damage based on an equivalent ellipse is proposed, which is helpful for better understanding the freezing–thawing damage law of asphalt pavement.

Effect of Fine Aggregate Gradation on Macro and Micro Properties of Cold Recycling Mixture Using Emulsified Asphalt

In order to explore the influence of fine aggregate on the macro and micro properties of cold recycling mixture using emulsified asphalt (CRME), mechanical and microscopic property tests were carried out. The indirect tensile strength (ITS), unconfined compressive strength (UCS) and triaxial shear strength of different fine aggregate gradation was measured for analyzing the effects of fine aggregate on the mechanical strength, triaxial shear resistance and fracture energy of CRME. Meanwhile, the surface morphologies and air voids distribution of different CRME were observed by scanning electron microscopy (SEM) and X-ray computed tomography (X-ray CT). The results show that fine aggregate has a significant effect on the mechanical strength and shear resistance of CRME. With the same water and asphalt content, the fracture energy and failure strain of the mixture with less fine aggregate (G3-2) decreased by 16.2% and 18.2%, respectively. The less content of powder there was, the fewer cement hydration products there were due to some cement being coated by emulsified asphalt and the “cement hydration products fiber” length being shorter. Approximately 70% of the AFt hydration products in the G3-2 mixture were in the range of 1–4 μm, while those in the G1 mixture were in the range of 4–8 μm. With the increase in filler content, the number of air voids in the volume range of 0.5 mm3 ≤ V < 5 mm3 in CRME decreased, and the number of air voids in the volume range of V < 0.5 mm3 significantly increased, while the equivalent radius of air voids decreased slightly with the increase in filler content.

Mechanical investigation and microstructure performance of a two-matrix continuous carbon fibre composite fabricated by 3D printing

This research aims at systematically investigating the mechanical performance of three-dimensional printed continuous carbon fibre reinforced thermoset and thermoplastic composites (CFRTSTPCs) under different processing aspects, such as the nozzle temperature, fibre impregnation and inter-/intra-layer boundness. For this purpose, the fused filament fabrication (FFF) technique is applied. Two-matrix continuous carbon fibre composites have indeed the potential to combine the easiness of impregnation of thermoset matrix composites with the versatility of thermoplastic matrix composites, especially in nozzle based additive manufacturing, but they have not yet been studied in a systematic manner. Firstly, thermo-gravimetric analysis and micro-computed tomography scanning of an impregnated fibre bundle are performed to obtain the raw materials thermal stability. Maximum flexural strength of 294 MPa and modulus of 32.5 GPa are obtained for the continuous carbon fibre specimens. Microscopic images and micro-CT analysis are then utilized to manifest the interfacial bonding and void distribution in the two and three-dimensions, respectively. Dynamic mechanical analysis is used to obtain the thermo-mechanical behaviour of the printed specimens. Finally, the processing window is provided based on the analysis of variance for different process parameters. This research shows that the printing process of CFRTSTPCs with controlled capabilities has excellent potential to manufacture low-cost composite parts in the industrial field.

Cosmic void baryon acoustic oscillation measurement: Evaluation of sensitivity to selection effects

Abstract Cosmic voids defined as a subset of Delaunay Triangulation (DT) circumspheres have been used to measure the Baryon Acoustic Oscillations (BAO) scale; providing tighter constraints on cosmological parameters when combined with matter tracers. These voids are defined as spheres larger than a given radius threshold, which is constant over the survey volume. However, the response of these void tracers to observational systematics has not yet been studied. In this work we analyse the response of void clustering to selection effects. We find for the case of moderate (<20 per cent) incompleteness, void selection based on a constant radius cut yields robust measurements. This is particularly true for BAO-reconstructed galaxy samples, where large-scale void exclusion effects are mitigated. Moreover, we observe for the case of severe (up to 90 per cent) incompleteness – such as can be found at the edges of the radial selection function – that an accurate estimation of the void distribution is necessary for unbiased clustering measurements. In addition, we find that without reconstruction, using a constant threshold under these conditions produces a stronger void exclusion effect that can affect the clustering on large scales. A new void selection criteria dependent on the (local) observed tracer density that maximises the BAO peak significance prevents the aforementioned exclusion features from contaminating the BAO signal. Finally, we verify, with large simulations including light cone evolution, that both void sample definitions (local and constant) yield unbiased and consistent BAO scale measurements.