Macroscopic Parameters Research Articles

Macroscopic and Microscopic Characteristics of a GDI Spray Under Various Thermodynamic Conditions

Article Macroscopic and Microscopic Characteristics of a GDI Spray Under Various Thermodynamic Conditions Jian Li 1, Lulu Li 1, Rujie Xiao 1, Yuanfei Liang 1, Shuyi Qiu 2, and Xuesong Li 2,* 1 SAIC GM Wuling Automobile Co., Ltd., 18 Hexi Rd, Liunan District, Liuzhou 545001, China 2 School of Mechanical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China * Correspondence: xuesonl@sjtu.edu.cn Received: 12 June 2023 Accepted: 9 August 2023 Published: 28 August 2023 Abstract: Gasoline direct injection (GDI) is the most common and advanced fuel supply strategy for gasoline engines. The fuel atomization quality and fuel/air mix degree determine the subsequent combustion efficiency and emissions. However, the engine works in complex conditions which have numerous thermodynamic boundary conditions, and the characteristics of fuel atomization also change accordingly. It is necessary to clarify the influence of various thermodynamic conditions on the GDI spray. In this work, three different types of optics diagnostic methods were utilized to capture the macroscopic and microscopic characteristics of a commercial GDI injector spray under various thermodynamic boundary conditions. Specifically, Mie-scattering photography was employed to get the macroscopic parameters; planar Mie-scattering photography was utilized to get the spray pattern; phase Doppler interferometry (PDI) was used to get the microscopic characteristic, i.e., the droplet size distributions. It is found from this study that higher injection pressure, lower ambient pressure, and lower ambient temperature would lead to longer penetration and larger plume width. Lower ambient pressure and higher ambient temperature would cause a smaller spray pattern. Higher injection pressure, lower ambient pressure, and higher ambient temperature would result in smaller droplet sizes.

Multiscale experimental characterisation of mode-I interfacial fracture behaviour of vitrimer composites

Vitrimer composites with bond- exchange reactions offer significant advantages in terms of repair and recyclability. The mechanical properties of such composites can be designed by modifying the epoxy/anhydride ratio, thus allowing their interface properties to be customised. In this study, the mode-I interfacial fracture properties of vitrimer carbon fibre composites with different epoxy/anhydride ratios are investigated experimentally and numerically. The results show that composites with an epoxy/anhydride group ratio of 1:0.5 exhibit the highest fracture toughness, with a maximum value of 1.6 mJ/mm2. Meanwhile, the analysis of the composites’ microscopic fracture morphology indicates their good bonding performance with carbon fibres. Subsequently, a multiscale numerical approach is developed to simulate the mode-I fracture response of composite laminates and establish a trilinear cohesive model to simulate the macroscopic interfacial fracture behaviour. In this approach, a matrix elastic–plastic constitutive model and the J-integral method are applied to obtain the stress distribution in the fibre-bridging phase via a double cantilever beam fracture test. The macroscopic fracture behaviour obtained via simulation is consistent with the experimental results. Therefore, the proposed multiscale numerical simulation method, which correlates the matrix properties with macroscopic fracture parameters, allows the interlaminar properties of composites with novel matrices to be evaluated effectively.

Influence of irradiation energy and damage coefficient on performance of CH3NH3PI3 photocell

An organic–inorganic hybrid perovskite as a light-absorbing layer has become a key material in many laminated-structures used in photon sensing devices. Some of these devices are referred to as Organic–inorganic hybrid perovskite (OIHP)-based devices. In recent days, OIHP applications have sky-rocketed in the world of flexible photo-electronics. Due to the higher radiation tolerances, OIHP-based solar cells have been recommended for terrestrial applications which is an application that require low fabrication costs that combines lightweight materials. However, it has been noticed that when it is used in extra-terrestrial environments, these photo cell devices experience premature failures once they interact with fast multispectral radiations in terrestrial spaces. Due to these premature failures, a similar solar cell from an (OIHP)-based perovskite material of methyl ammonium lead iodide (CH3NH3PI3) was investigated as an observer layer under a multi-spectral simulated illumination. After simulation, data for the expected photocurrent flowing through junction components on a glass substrate coated with a thin layer of Titanium dioxide (TiO 2) film was obtained. The influence of energy of irradiation on damage coefficients, current density, photovoltage and I–V characteristic profile curves were determined and investigated. Some general common macroscopic parameters for photon sensing were analyzed on three dimensions (3D) to determining the minority charge carriers and their induced photo-voltages with respect to junction recombination velocities. The obtained computed macroscopic parameters were incorporated into the Quite Universal Circuit Simulator software for simulation. It was established that damage coefficient influenced the I–V curve and an accumulation of charge carriers magnifies the probability of plasmons initiating degradation of the absorber layer. The atoms in the CH3NH3Pl3 crystal lattice system uniformly recoils at resonance and transport the maximum charge carriers across the P-N junction capable of creating a significant damage concentrated within a few micrometer ranges on the surface that may even extend between 0.39 to about 1.01 micrometers in size. This paper therefore evaluates the influence of irradiation energy and damage coefficient in a hybrid CH3NH3PI3 mono-facet crystal structure on exposure to multi-spectral illumination at varied irradiation energies.

A Cavity-Based Micromechanical Model for the Shear-Band Failure in Metallic Glasses Under Arbitrary Stress States

Abstract Deformation and fracture of metallic glasses are often modeled by stress-based criteria which often incorporate some sorts of pressure dependence. However, detailed mechanisms that are responsible for the shear-band formation and the entire damage initiation and evolution process are complex and the origin of such a pressure dependence is obscure. Here, we argue that the shear-band formation results from the constitutive instability, so that the shear-band angle and arrangements can be easily related to the macroscopic constitutive parameters such as internal friction and dilatancy factor. This is one reason for the observed tension-compression asymmetry in metallic glasses. The free volume coalescence leads to precipitous formation of voids or cavities inside the shear bands, and the intrinsic “ductility” is therefore governed by the growth of these cavities. Based on a generalized Stokes–Hookean analogy, we can derive the critical shear-band failure strain with respect to the applied stress triaxiality, in which the cavity evolution scenarios are sharply different between tension-controlled and shear/compression-dominated conditions. This is another possible reason for the tension-compression asymmetry. It is noted that diffusive-controlled cavity growth could also be the rate-determining process, as suggested by the recent measurements of shear-band diffusivity and viscosity that turn out to satisfy the Stokes–Einstein relationship. This constitutes the third possible reason for the tension-compression asymmetry.

Study on the Periodic Collapse of Suspended Sandstone Interlayer under Coupled Thermo–Hydro–Mechanical Environment

In the process of in situ heat injection mining of coal seams, a circular combustion chamber will gradually be formed. However, for the interlayer coal seam, the interlayer will gradually suspend in the combustion chamber. When the critical distance is reached, the initial collapse and periodic collapse will occur, which will affect the flow field distribution and extraction efficiency of combustion gas. In order to study the initial and periodic collapse steps of interlayer in real-time high temperature and high-pressure thermo–hydro–mechanical (THM) coupling environments, sandstone specimens were collected from the field, and the macroscopic mechanical parameters of sandstone interlayer were tested using a self-developed thermo–hydro–mechanical coupling tester. The mechanical parameters (e.g., triaxial compressive strength, elastic modulus, Poisson’s ratio) of sandstone under different stress conditions were obtained. Then, based on the elastic thin plate theory, the mechanical modeling of the annular sandstone interlayer is carried out and the preceding mechanical parameters are brought into the generated analysis equation. Thus, the periodic collapse step of the suspended circular sandstone interlayer is obtained. The study results show that: (1) the macroscopic physicomechanical parameters of the sandstone interlayer do not vary monotonically with temperature—a slight increase in macroscopic parameters occurs at 400°C; and (2) the periodic caving pace of the sandstone interlayer decreases with the increase in the number of collapses. With the increase of temperature, the periodic caving pace of the sandstone interlayer decreases first, then increases, and then decreases. It gradually decreases with the increase of surrounding pressure. The research results of this paper can provide theoretical guidance and technical support for in situ heat injection mining technology.

Generic role of the Dzyaloshinskii–Moriya interaction in nanocrystalline ferromagnets

Motivated by recent experimental polarized neutron results, we present a numerical micromagnetic study of the interfacial (intergrain) Dzyaloshinskii–Moriya interaction (DMI) in nanocrystalline terbium. We demonstrate that the DMI-induced spin misalignment between adjacent nanograins is the reason for the formation of the asymmetric positive-negative pattern seen in polarized neutron scattering experiments. Analysis of the remagnetization process suggests the generic impact of the DMI on the macroscopic magnetic parameters of polycrystalline defect-rich materials.

Identifying anisotropic structural features beneath the human nail with differential polarization parameters

In this work, we report a method of identifying anisotropic structural features beneath the nail with differential polarization parameters. First the form of the differential Mueller matrix of medium in terms of the average and the fluctuation parameters of the differential polarization parameters in backscattering configuration is derived. The results are then employed to identify anisotropic structures beneath the human nail. For the first time, to our knowledge, it was found that collagen fibrils of the layers of epidermal cells of nail bed, the layers of actively dividing cells of the stratum germinativum of nail matrix, and the longitudinal striations in nail root can be related to the covariance of the linear birefringence along the x-y laboratory axes and the 45°axes. Although some tissue constituents can be observed in images of both macroscopic and differential parameters, the tissue components revealed by differential polarization parameters cannot be discerned in any image of the macroscopic parameters.

Ultimate bearing capacity of intact rocks at tip of large-diameter rock-socketed piles considering internal micro-cracks

In the design of large-diameter rock-socketed piles, the ultimate bearing capacity of intact rocks under the pile tip (qb ) is often required to be predicted, especially for rock-socketed end-bearing piles. Existing approaches for calculating qb establish an empirical relation with the macroscopic parameters of rock layers, but the research on the microscopic parameters inside intact rocks is insufficient. This study provides a theoretical method for calculating qb from a micro perspective and implements it in MATLAB, in which the integral stress of the Mindlin solution within the circular region at the pile base was selected as the stress state of the theoretical calculation regions, and the tension– or compression–shear mixed mode I–II criterion was selected as the failure criterion of micro-cracks inside intact rocks. Six model piles with measured ultimate end-bearing capacities were analyzed to validate the proposed solution. The results showed that the failure ranges of intact rocks under an identical base load for analytical analyses are comparable with those obtained by model tests, which confirms the rationality of the theoretical approach. Then, the failure zone of intact rocks under different working loads of pile base was explored. Finally, parametric studies were conducted using the proposed solution to explore the effects of rock properties and pile dimensions.

Macroscopic Parameters of Fuel Sprays Injected in an Optical Reciprocating Single-Cylinder Engine: An Approximation by Means of Visualization with Schlieren Technique.

This paper proposes a sensor system for an internal combustion engine based on a new vision-based algorithm supported by the Schlieren sensorization technique, which allows to acquire the macroscopic parameters of the fuel spray injected in a reciprocating internal combustion engine under unmanned aerial vehicle-like conditions. The sensor system proposed here is able to automatically determine the spray cone angle, its area and its penetration. In addition, the external surface and the volume of the fuel spray is estimated together with the injector opening delay and the ignition delay. The developed algorithm was experimentally tested using a conventional diesel fuel in a single-cylinder engine with an optically adapted head but with easy application and other configurations of reciprocating internal combustion engines. These spray macroscopic parameters allow to analyze, among others, the effect of the spray on the development of both the injection and combustion processes under different operating conditions. The estimation of the external surface of the spray makes it possible to determine the amount of fuel in the spray that is in contact with the surrounding air, with the possibility to link this parameter to the combustion efficiency and emission reduction. Consequently, obtaining the injector opening delay and the ignition delay are important parameters in the combustion phenomenon. In addition, the ignition delay has a great influence on both the engine design and its performance in the study of the air-fuel blending process, in the efficient combustion process and in the reduction of emissions.

Study on structural optimization of braid‐and‐lay integrated carbon fiber reinforced polymer for metro bogie

AbstractCarbon fiber reinforced polymer is an effective solution for replacing metal materials and achieving lightweight, and both three‐dimensional (3‐D) braided composites and prepreg laminated composites have their strengths and weaknesses. Using only one forming process can be challenging to meet the performance requirements of structural components under complex operating conditions. To effectively reduce the production cost and cycle time of large structural components while ensuring the mechanical properties of the structure, this article proposes a novel three‐dimensional braided and prepreg‐layered (braid‐and‐lay) composite forming process that is studied in the context of metro bogies. First, the performance advantages of braid‐and‐lay composites were verified through experimental methods. Then, a multi‐scale analysis method, combining experimental and finite element analysis, accurately predicted the macroscopic elastic parameters of the three‐dimensional braided composite with an error of less than 10% compared to the experimental values. Finally, a structural optimization design of the braid‐and‐lay composite metro bogie was carried out based on the predicted elastic parameters. The results show that the mass of the structure was reduced by 15.33%, from 272.103 to 230.386 kg, while ensuring that the displacement and stress responses do not exceed the constraint range.Highlights Proposed a braid‐and‐lay integrated composite forming process. A multi‐scale analysis method, combining experimental and finite element analysis, was used to predict the modulus. The effect of braiding parameters on modulus prediction was investigated. The influence of the forming process and structural parameters on the performance of the metro bogie was investigated. The lightweight design of the metro bogie is effectively realized.

Frontier Molecular Orbital Offset as an Empirical Descriptor for Predicting Short Circuit Current of Nonfullerene Organic Solar Cells

An efficient computational approach, in contrast to the trial‐and‐error experiment process, for predicting, characterizing, and optimizing the macroscopic performance parameters (e.g., short‐circuit current density (Jsc)) of nonfullerene acceptors‐based organic solar cells (OSCs) remains a rarely addressed and complicated challenge. In this work, a data‐driven approach is used to predict the electrical performance of nonfullerene OSCs and reveal their charge transfer behaviors. The eXtreme Gradient Boosting (XGBoost) model within empirical descriptors is used to understand the governing feature for enhancement of Jsc, which is vital for the design and discovery of new donor/nonfullerene acceptor photoactive layers for photovoltaic applications. Through the well‐trained XGBoost model and SHapley Additive exPlanations theory, the descriptors impacting the Jsc of nonfullerene OSCs are further explained and analyzed. Remarkably, the XGBoost model combines four empirical descriptors to achieve an impressive prediction accuracy (R2 > 0.8). The results from data‐driven approaches prove that the lowest unoccupied molecular orbital (LUMO) offset (between donor and acceptor) plays the most significant role in increasing the Jsc values of nonfullerene OSCs. Moreover, this study highlights the effect of LUMO offset on the photoinduced charge transfer process of donor/non‐fullerene acceptor blends, which might pave the way toward rapid and precise energy‐level tuning of efficient OSC materials.

The investigation of flocculation and deposition of heavy components in the crude oil tank based on experiment and molecular simulation

With the implementation of the “3060” carbon neutrality policy, the cancellation of external insulation has led to the increasingly serious deposition of heavy components in petroleum storage tanks. However, there are few studies on the flocculation and deposition behavior of industrial complex crude oil systems during the entire storage period in tanks. This study used an equivalent crude oil tank system to systematically investigate the flocculation and deposition behavior of industrial crude oil systems during storage. Static settling experiments were conducted for the entire storage period (32 days) to measure changes in oil parameters such as density, wax appearance temperature (WAT), gel point, and particle size at different heights in the tank. In addition, a full-component molecular system for crude oil was constructed, and molecular dynamics (MD) simulation was used to reveal the flocculation and aggregation mechanisms of heavy components in crude oil systems for the first time. The result showed that the maximum density difference between the upper and lower of the test tank is 14 kg/m3 and the marked stable time of sedimentation is 163 h. The maximum increment of the WAT appears at the bottom of the tank with the value increasing from 38.17 °C to 45.75 °C. The microscopic observations are consistent with the changes in macroscopic parameters. The wax is very prone to aggregation and wax crystals show a face-to-face sticking state. As for asphaltenes, the degree of aggregation is weaker than that of wax molecules, and the aggregation state mainly shows two manners: T-shape sticking and face-to-face sticking. This study can provide the theoretical basis for tackling the tank bottom sediment.

Numerical simulation of diesel particulate filter performance optimization through pore structure analysis

Based on the theory of spherical filled bed, the internal porous media filter wall of the Diesel Particle Filter (DPF) is assumed to fill the filter wall of the unit cell. Since particle trapping by DPF is a dynamic process, the particle deposition characteristics inside DPF are simulated by numerical simulation in this paper. The influence of macroscopic incoming flow parameters and microstructural parameters on DPF filtration performance is investigated, and then the optimization window that can improve DPF filtration performance is explored. The results show that increasing the exhaust temperature and incoming particle concentration leads to an increase in the filtration efficiency and pressure drop of DPF, while the higher the filtration velocity, the lower the filtration efficiency of DPF. In addition, the larger the porosity, the higher the filtration efficiency and pressure drop of DPF, while the increase in the average pore size and pore size distribution range leads to a decrease of the filtration performance of DPF. On this basis, evaluation indexes that can evaluate the filtration performance of DPF are proposed to provide a theoretical basis for optimizing the substrate parameters of DPF.

Electromagnetic Monitoring of Modern Geodynamic Processes: An Approach for Micro-Inhomogeneous Rock through Effective Parameters

This study focuses on microscale anisotropy in rock structure and texture, exploring its influence on the macro anisotropic electromagnetic parameters of the geological media, specifically electric conductivity (σ), relative permittivity (ε), and magnetic permeability (μ). The novelty of this research lies in the advancement of geophysical monitoring methods for calculating cross properties through the estimation of effective parameters—a kind of integral macroscopic characteristic of media mostly used for composite materials with inclusions. To achieve this, we approximate real geological media with layered bianisotropic media, employing the effective media approximation (EMA) averaging technique to simplify the retrieval of the effective electromagnetic parameters (e.g., apparent resistivity–inversely proportional to electrical conductivity). Additionally, we investigate the correlation between effective electromagnetic parameters and geodynamic processes, which is supported by the experimental data obtained during monitoring studies in the Tien Shan region. The observed decrease and increase in apparent electrical resistivity values of ρk over time in orthogonal azimuths leads to further ρk deviations of up to 80%. We demonstrate that transitioning to another coordinate system is equivalent to considering gradient anisotropic media. Building upon the developed method, we derive the effective electric conductivity tensor for gradient anisotropic media by modeling the process of fracturing in a rock mass. Research findings validate the concept that continuous electromagnetic monitoring can aid in identifying natural geodynamic disasters based on variations in integral macroscopic parameters such as electrical conductivity. The geodynamic processes are closely related to seismicity and stress regimes with provided constraints. Therefore, disasters such as earthquakes are damaging and seismically hazardous.

Micro-scale reconstruction and CFD-DEM simulation of proppant-laden flow in hydraulic fractures

A comprehensive investigation of the dynamical characteristics of proppant-laden flow systems in hydraulic fractures is important for the development of unconventional oil and gas resources. In this paper, we combine the micro-scale reconstruction technique and CFD-DEM method to numerically investigate the mobility and distribution rules of proppant-laden fluid in rough hydraulic fractures. To characterize realistic fracture surface morphology, six synthetic fracture models were assembled based on optical scanning data of real shale from three sets of hydraulic fracturing experiments. In order to accurately simulate the fluid-particle two-phase flow in rough fractures, the lift forces and particle rolling effect are considered in the CFD-DEM model. First, the effectiveness of the used CFD-DEM solver was validated by comparing it to the experimental data. We then examined mechanisms for the typical flow behaviors of proppant particles and fracturing fluid in smooth and rough fractures. Subsequently, the surface area ratio of the synthetic fracture model is adopted to characterize the cross-scale relationship between the micro-scale proppant distribution and fracture’s geometric features induced by the macroscale fracturing parameters (i.e., confining stress, fluid viscosity, flow rate, and sand ratio). Lastly, the parameter effects of the fracturing fluid, proppant particle, and fracture aperture on the dynamic characteristics of particulate flow in the hydraulic fracture are further discussed. In summary, the presented numerical model and findings can help better understand particle transport and distribution in real rock fractures and bridge the connectivity of the micro-scale particle flow and macroscopic fracturing parameter, which is vital for hydraulic fracturing process optimization.

An extended universal morphological model for concrete mode‐I fracture: Formulations and preliminary verifications

AbstractThe purpose of this study is to develop a systematic meso‐level theoretical modeling approach for analyzing the mode‐I fracture failure behaviors of concrete. Firstly, the crack model is developed in a way to be equivalent to the continuum model at the macro‐level. Secondly, an extended universal morphological model (XUMM) for concrete mode‐I fracture analysis is proposed at the meso‐level. Afterwards, both the mesoscopic fracture characteristics and the macroscopic mechanical parameters of concrete are theoretically deduced based on the proposed XUMM. Comparison with existing meso‐level test results shows that the predictions from the XUMM have good consistency, but offsets are obvious as well. At last, the XUMM is calibrated using the limit state method and preliminarily verified via mesoscale numerical simulations.

Numerical investigation of effect of surface pattern and rotation on power-law fluid flow and heat transfer around a cylinder in laminar flow regime

We have studied the effect of surface topography, fluid behavior, and rotation on fluid flow and heat transfer phenomena over a cylinder. In this study, we have incorporated a sinusoidal surface topography to account for the impact of surface patterns and a power-law model to include fluid behavior. The governing equations are solved numerically for a range of pattern frequency (ω=5 and 11), pattern amplitude (δ=0.01 and 0.1), power-law index (0.4≤n≤1.6), Prandtl number (1≤Pr≤100), rotational speed (0.5≤α≤2), and Reynolds number (5≤Re≤40). In particular, the study aims to determine the degree to which various macroscopic parameters, such as the drag and lift coefficients, the average Nusselt number in relation to the Reynolds number, the Prandtl number, the rotating speed, and the power-law index, vary. In this range of Reynolds number, the flow around a circular cylinder is steady, with two symmetric vortices in the rear side. The sliding mesh method is used to deal with dynamic interface between solid and fluid. The streamlines are drawn to visualize the flow field around the patterned cylinder. For a non-rotating patterned cylinder, small recirculation zones are observed over the trough, which are absent in circular cylinders. The size of these recirculation regions increases on increase in Reynolds number and power-law index. On adding rotation to the cylinder, these recirculation zones move away from the cylinder and appear over the crest. On increasing the rotating speed of the cylinder, the frontal vortices disappear. The enveloping vortex gets larger with increase in rotating speed and power-law index. The size of the rear detached vortex increases with power-law index and Reynolds number and decreases with rotating speed. It is observed that the results are contrasted with the previous studies on smooth circular cylinder. The drag force acting on the patterned cylinder is seen to be reduced. Compared to a circular cylinder, a significant reduction in drag can be achieved by choosing suitable value of pattern frequency (ω) and amplitude (δ). Overall, there is a decrease in the amount of drag reduction as the Reynolds number increases. The behavior of the fluid has a considerable influence on the reduction of drag. It has been observed that shear-thickening fluid significantly contributes to the enhancement of drag reduction. For a higher value of pattern frequency and amplitude (ω=11,δ=0.1), the drag force reduces significantly for Newtonian and shear-thickening fluids at higher rotating speed (α=2). Also, the pattern frequency and amplitude substantially impact the average Nusselt number. On increase in pattern frequency and amplitude, a progressive decrease in the average Nusselt number is observed. Compared to shear-thinning and Newtonian fluid, shear-thickening fluid exhibits a greater reduction in average Nusselt number. One correlation is provided at the end to show the relationship between the average Nusselt number, the Prandtl number, the Reynolds number, the rotating speed, and the power-law index.

Patterns of localized deformation at pre-fracture stage in carbon steel – stainless steel bimetal

The work is devoted to the study of strain localization at macroscale level during parabolic mechanical hardening and pre-fracture under quasi-static loading of a carbon steel – stainless steel bimetal. The problem of estimating the scale of the phenomena that determine plasticity is decisive in the development of any theories of plastic deformation, in particular, dislocation theories. The main difficulty in constructing such theories is the reconciling the dislocation scales, characteristic for most deformation and mechanical hardening mechanisms, with macroscopic parameters of deformation processes. In the framework of the autowave model of localized plastic deformation, this problem can be reduced to the possibility of obtaining parameters from the results of macroscale observations of localized plastic flow development. During the experiments, it was confirmed that in a bimetal at any forming stage, a specific pattern of localization centers distribution is spontaneously generated - a pattern of localized plastic flow. The shape of such patterns is determined by the law of mechanical hardening acting in the material. It is shown that the observed localization patterns can be used as an informative feature in predicting the plasticity margin. In the process of uniaxial tension at the stage of parabolic mechanical hardening of the bimetal, the deformation mode is realized with the formation of several potential fracture centers. It was established that at the pre-fracture stage, during the time evolution of the wave pattern of deformation localization, the zone of active plastic deformation narrows, but the number of centers in it either remains the same with a decrease in the distance between them, or even increases. The result of this process is the formation of a macroscopic neck, and then fracture. At the pre-fracture stage, the collapse point indicates the place of future fracture and signals the need to stop the deformation process in order to avoid the fracture of the bimetallic material. Thus, the well-known manifestation of deformation macroscopic localization – formation of a neck – is preceded by complex phenomena of mutually coordinated motion of localized plasticity centers at the pre-fracture stage.

Effect of vibration direction on the packing of sphero-cylinders

Particle packing is widely encountered when coping with granular materials, while mechanical vibration is usually used for packing densification. Vibration direction has been proven to be crucial for the ordered packing of spherical particles, but there are few reports for non-spherical ones in this regard. In this study, the effect of vibration direction on the macroscopic and microscopic packing parameters of sphero-cylinders are systematically examined using discrete element method (DEM). Due to the anisotropic shapes of sphero-cylinders, their packing characteristics are much richer and also more complex than those of spheres. It is found that vibration direction affects both the packing density and the packing structure of sphero-cylinders through tuning their orientation distributions and contact modes. Moreover, vibration direction plays a significant role in determining the optimal vibration intensities for dense packing. When the sphericity of Voronoi cell decreases and/or the density increases, the Nematic order parameter increases accordingly. Besides, no obvious relationship between the packing density and the average contact number is observed.

Ecotoxicity Evaluation of Industrial Waste and Construction Materials: Comparison Between Leachates from Granular Steel Slags and Steel Slags-Containing Concrete Through a Plant-Based Approach

Steel slags, the main waste product from the steel industry, may have several reuse possibilities. Among others, building applications represent a crucial field. However, the potential impact of harmful substances on the environment should be assessed. The aim of this study was to assess the phytotoxicity of steel slags (SS) and concrete mixtures cast with a partial replacement of SS (CSS). Leaching tests were carried out on four SS and four CSS according to EN 12457-2 and UNI EN 15863, respectively. Each leachate was assayed using root elongation tests on 30 seeds of Allium cepa, Cucumis sativus, and Lepidium sativum, respectively, and on 12 bulbs of A. cepa. The latter also allowed the analysis of other macroscopic parameters of toxicity (turgidity, consistency, colour change and root tip shape) and the evaluation of the mitotic index on 20,000 root tip cells per sample. None of the samples induced phytotoxic effects on the organisms tested: all samples supported seedlings emergence, verified by root elongation comparable to, or even greater than, that of the negative controls, and did not affect cell division, as evidenced by mitotic index values. The absence of phytotoxicity demonstrated by the leachates allows SS and SS-derived concrete to be considered as reliable materials suitable for use in civil constructions or in other engineering applications, with economic and environmental advantages, such as the reduction of the final disposal in landfills as well as the consumption of natural resources.