Behavior Of Bulk Material Research Articles

Quantifying the influence of single particle shape on crushing characteristics of recycled aggregates: Experimental and numerical insights

Exploring the interplay between shapes and crushing characteristics of recycled aggregates (RA) is pivotal for understanding their macro-mechanical behavior in bulk materials. This investigation quantitatively characterizes the shapes of recycled bricks (RB), recycled concrete (RC), and recycled mortar (RM) particles, and assesses their single-particle crushing characteristic. Key focus areas include the analysis of crushing modes, fractal attributes, strength, and energy, supplemented by a comparative study using discrete element method (DEM) simulations to predict outcomes for particles of specific sphericity. Findings reveal that the shapes of RA particles are mainly disk, block, blade and bar, with particle size showing negligible influence on these forms. Crushing behaviors are categorized into penetrating fracture, corner rupture, and overall fragmentation, closely linked to particle sphericity. Notably, an increase in sphericity leads to a reduction in fractal characteristics of RA, refining the gradation distribution from broad to narrow spectrums. An exponential relationship is identified between the crushing strength of RA and particle sphericity, a pattern also mirrored in the correlation between crushing energy and sphericity, thereby underscoring the significant influence of particle shape. These relationships facilitate predictions regarding the crushing strength and energy based on sphericity. While numerical simulations broadly align with experimental data, discrepancies in the crushing energy of highly spheric particles necessitate adjustments, resulting in a modified predictive equation for crushing energy. This work enriches the understanding of RA crushing behavior, offering invaluable insights for predicting the single-particle strength and deformation characteristics across different sphericities, thus advancing material engineering and recycling practices.

МЕТОДИКА И РЕЗУЛЬТАТЫ МОДЕЛИРОВАНИЯ В «Flow Simulation» «SOLIDWORKS 2018» ПРОЦЕССА ОБТЕКАНИЯ ЛОПАТКИ СМЕСИТЕЛЯ КОРМОВ

It is impossible to obtain high-quality combined feeds without effective mixers. To improve them, you can use programs that simulate the behavior of bulk materials, but most of them are inaccessible and difficult to master. The use of more accessible software that simulates the process of fluid flow - “Flow Simulation” “SOLIDWORKS 2018” is proposed for assessing the movement of bulk materials. A previously developed design scheme was used, in which the working bodies of the mixer are combined and contain several sections of blades with reasonable geometric parameters for different purposes (transportation and mixing). A model of the scapula has been made. The parameter under study was the installation angle of the mixer blades relative to the shaft of the working element. The criterion for selecting blade installation angles was the presence of a maximum number of flow areas with velocities different from those specified for the overall material flow. As a result of the simulation, flow velocity distributions were obtained at given blade installation angles with a gradation step of flow velocity fields of 0.393 m/s. The limit values for the installation angles of the mixer blade are set from 0° to 60°. This criterion is met by blade installation angles from 45° to 0°. It is shown that the results of modeling the flow around a flat blade with given dimensions generally do not contradict the results of existing studies. Further research will be aimed at assessing the simulation results based on full-scale experiments with subsequent adjustments.

Sensitivity Analysis of the DEM Model Numerical Parameters on the Value of the Angle of Repose of Lunar Regolith Analogs

Abstract The discrete element method (DEM) is a numerical technique used in many areas of modern science to describe the behavior of bulk materials. Terramechanics of planetary soil analogs for in situ resource utilization activities is a research field where the use of DEM appears to be beneficial. Indeed, the close-to-physics modeling approach of DEM allows the researcher to gain much insight into the mechanical behavior of the regolith when it interacts with external devices in conditions that are hard to test experimentally. Nevertheless, DEM models are very difficult to calibrate due to their high complexity. In this paper, we study the influence of fundamental model parameters on specific simulation outcomes. We provide qualitative and quantitative assessments of the influence of DEM model parameters on the simulated repose angle and computational time. These results help to understand the behavior of the numerical model and are useful in the model calibration process.

Strain field in Ni2MnGa magnetic shape memory alloys with different twin densities under combined tensile and magnetic loading

This study investigates the strain fields developed in two Ni2MnGa samples, with fine and coarse twin structures, respectively when loaded in tension and/or with a magnetic field. The strain fields have been recorded using the digital image correlation technique, which allowed for the observation of the strain field over the entire sample as it evolves with load. This allows for visual observation of the evolution of the sample’s twin microstructure. This investigation provides a more comprehensive insight into the localized and bulk material behavior than the traditional strain measurement techniques used in previous studies. The results show that the twin density, the uniformity of the magneto-mechanical loading along the sample, and the presence of pinning sites are all contributing to the profile of the tensile strain field. Particularly, the presence of pinning sites and the emergence of perpendicular twin boundaries along the sample inhibit full variant reorientation and recovery. Both samples showed no visible signs of damage or crack formation during tensile testing, and their magneto-mechanical response in tension and compression was found to be similar, but there is a clear tension/compression asymmetry.

Residual strain investigation of a polycrystalline quartzite rock sample using time-of-flight neutron diffraction

In this work, we studied the residual micro lattice strain of an onyx sample, which is a micro- to the cryptocrystalline variety of the mineral quartz SiO2. That the investigation has been carried out using in-situ stress experiments with the time-of-flight neutron diffraction method. The aim of the study is to investigate residual lattice strains and pressure directions in the sample using time-of-flight neutron diffraction, which is a powerful tool for the study of the residual strain behavior in bulk materials, like geological rock samples containing large grains. The residual strain was detected in different sample directions turning the sample in steps of 30° by 180° around the cylindrical z-axis. These experiments have been performed at the time-of-flight neutron strain diffractometer EPSILON, situated on the pulsed neutron source IBR-2M of the Joint Institute for Nuclear Research in Dubna, Russia. The results of this study will provide insights into the compressional and tensional residual strain of the crystallographic lattice planes, and will have implications for our understanding of the tectonic history of this region. These different strains are arranged in the sample by a sinusoidal distribution in radial directions.

Crystal Plasticity simulations of in situ tensile tests: A two-step inverse method for identification of CP parameters, and assessment of CPFEM capabilities

As the computational capability of modern computers increases, the Crystal Plasticity Finite Element Method (CPFEM) becomes more and more popular in materials science to model the mechanical behaviour of polycrystals. Indeed, such analysis provides extensive information about local mechanical fields (such as plastic strain and stress), which can be useful for understanding the behaviour of bulk materials. However, estimating the parameters of the CP constitutive laws is still challenging because they are not directly related to the macroscopic behaviour of the polycrystalline aggregates. Thus, one way to identify such parameters is by inverse analysis from CPFEM simulations. However, such approach is usually extremely time consuming. This paper proposes a two-step optimization scheme to determine these coefficients. The first step is based on a simple model, similar to that proposed by Sachs back in 1928. The second step is based on CPFEM simulations, to be compared with experimental data acquired by an in situ tensile test and full-field measurements made by High-Resolution Digital Image Correlation (HRDIC). The uniqueness of the solution found by inverse analysis is studied and ways to solve the local minima issues are provided. Finally, the ability of CPFEM to replicate an in situ tensile test is assessed.

Modeling the evolution of representative dislocation structures under high thermo-mechanical conditions during Additive Manufacturing of Alloys

Mesoscale simulations of discrete defects in metals provide an ideal framework to investigate the micro-scale mechanisms governing the plastic deformation under high thermal and mechanical loading conditions. To bridge size and time-scale while limiting computational effort, typically the concept of representative volume elements (RVEs) is employed. This approach considers the microstructure evolution in a volume that is representative of the overall material behavior. However, in settings with complex thermal and mechanical loading histories careful consideration of the impact of modeling constraints in terms of time scale and simulation domain on predicted results is required. We address the representation of heterogeneous dislocation structure formation in simulation volumes using the example of residual stress formation during cool-down of laser powder-bed fusion (LPBF) of AISI 316L stainless steel. This is achieved by a series of large-scale three-dimensional discrete dislocation dynamics (DDD) simulations assisted by thermo-mechanical finite element modeling of the LPBF process. Our results show that insufficient size of periodic simulation domains can result in dislocation patterns that reflect the boundaries of the primary cell. More pronounced dislocation interaction observed for larger domains highlight the significance of simulation domain constraints for predicting mechanical properties. We formulate criteria that characterize representative volume elements by capturing the conformity of the dislocation structure to the bulk material. This work provides a basis for future investigations of heterogeneous microstructure formation in mesoscale simulations of bulk material behavior.

Characterization of fibronectin properties by integrated micro-fluidic experiments and fluid-structure interaction simulations

Fibronectin (Fn) has been observed to assemble in the extracellular matrix (ECM) of cell culture and stretch in response to the external force. The alteration of molecule domain functions generally follows the extension of Fn. Several researchers have investigated fibronectin extensively in molecular architecture and conformation structure. However, the bulk material behavior of the Fn in the ECM has not been fully depicted at the cell scale, and many studies have ignored physiological conditions. Conversely, microfluidic techniques that explore cellular properties based on cell deformation and adhesion have emerged as a powerful and effective platform to study cell rheological transformation in a physiological environment. However, directly quantifying properties from microfluidic measurements remains a challenge. Therefore, it is an efficient way to combine experimental measurements with a robust and reliable numerical framework to calibrate the mechanical stress distribution in the test sample. In this paper, we present a monolithic Lagrangian fluid–structure interaction (FSI) approach within the Optimal Transportation Meshfree (OTM) framework that enables the investigation of the adherent Red Blood Cell (RBC) interacting with fluid and overcomes the drawbacks of the traditional computational tools such as the mesh entanglement and interface tracking, etc. This study aims to assess the material properties of the RBC and Fn fiber by calibrating the numerical predictions to experimental measurements. Moreover, a physical-based constitutive model will be proposed to describe the bulk behavior of the Fn fiber inflow, and the rate-dependent deformation and separation of the Fn fiber will be discussed.

Long-term mechanical performance of 3D printed thermoplastics in seawater environments

This study investigates the effects of 3D-printed thermoplastics' long-term exposure to ocean water. The work focuses on seawater diffusivity rates and mechanical performance to discuss material candidates for long-term undersea structures. Several commonly available thermoplastics were printed using Fused Deposition Modeling and then submerged in an ocean water solution for a prolonged period at elevated temperatures. The thermoplastics studied included Nylon, ABS, PLA, PCTG, PETG, and ASA. The different temperatures corresponded with distinct accelerated rates of water mass diffusion. The solution's water level, temperature, and salinity were monitored and maintained during the accelerated weathering process. The total mass of each specimen and its elastic modulus were recorded daily using a precision scale and a Dynamic Mechanical Analyzer machine. The change in mass was used to calculate the activation energy of each material system by defining the degradation to have an Arrhenius behavior and using a new polynomial fit-based technique. The new polynomial fit-based method was robust compared to a one-dimensional system that uses Fick's law of diffusion. Results also showed that the 3D printed structures, regardless of their composition, are susceptible to extremely high diffusivity rates compared to their bulk material behavior. Lastly, mechanical properties decreased for all polymers, and the stiffness of the aged specimens was proportionally affected by the change in mass.

Time-dependent finite-difference model for transient and steady-state analysis of thermoelectric bulk materials

A mathematical model of coupled thermoelectricity is presented to investigate the transient and steady-state behaviour of thermoelectric bulk material. Governing partial differential equations (PDEs) for the coupled thermal and electrical behaviour of the thermoelectric model are discretised using the explicit finite-difference method. Differencing schemes like Upwind and Lax–Wendroff methods are employed to obtain solutions for the first-order hyperbolic PDEs, whereas FTCS (Forward Time, Centred Space) scheme is employed to solve second-order parabolic PDEs. Courant-Friedrichs-Lewy and Von Neumann stability analyses are done to ensure the stability and convergence of the model. The model considers the temperature dependency of thermal conductivity, electrical conductivity, and Seebeck coefficient of the P/N materials separately. and accounts for the Seebeck, Peltier, and Joule-Thomson effects in thermoelectric materials. The new model is practically useful to predict the transient and steady-state behaviours of a thermoelectric device with multiple P-N elements. The results of the presented finite-difference model are proven to agree well with experimental values as well as 3D simulations with ANSYS®.

Relating the kinetics of grain-boundary complexion transitions and abnormal grain growth: A Monte Carlo time-temperature-transformation approach

Grain boundaries undergo thermally-activated, first-order transitions that result in discontinuous changes of interfacial properties. Importantly, grain boundary transitions lead to changes in bulk material properties (e.g., embrittlement) and/or behavior (e.g., abnormal grain growth). Numerous studies have been completed on the equilibrium states of grain boundaries and their transitions (i.e., complexion transitions), but there have been far fewer investigations of complexion transition kinetics; complexion transitions occur on the atomic-scale and are therefore challenging to detect experimentally. In this work, a 3D Potts grain growth model with stochastic complexion transitions was employed to investigate complexion transition kinetics. A Johnson-Mehl-Avrami-Kolmogorov (i.e., JMAK) approach was used to extract nucleation and growth rates (i.e., transformation rates), while point process analyses and correlation functions were used to infer complex interrelated nucleation and growth events. Time-temperature-transformation (TTT) diagrams, in particular grain-boundary complexion, transformed grain, and abnormal grain TTT diagrams, were constructed to summarize the progress of complexion-related transformations. Such diagrams relate complexion-induced grain growth to the underlying complexion transitions and, in the case of abnormal grain growth (AGG), permit one to assess the role of AGG as a temperature-dependent, time-displaced indicator of complexion transitions. Overall, this work details a theoretical framework that can be used to better understand complexion transition kinetics as well as to develop tools for the design of bulk microstructures.

Controlling phase separation behavior of thermo-responsive ionic liquids through the directed distribution of anionic charge

Thermoresponsive ionic liquids (TR-ILs) are room temperature liquid salt electrolytes with dynamic physical properties which have been hailed as potential solutions to inefficiencies in energy storage and material separations. That potential is hindered by the sensitivity of TR-IL phase separation to chemical structure. An accurate assessment of the effect of ion structure on molecular bonding is required for rational design as bonding changes translate to bulk material behavior. We systematically modify the structure of TR-ILs which exhibit either lower critical solution temperature (LCST) or upper critical solution temperature (UCST) phase separation to isolate the effect of specific types of bonding on eight tetrabutylphosphonium benzoate derived ILs through COSMO-RS sigma profile analysis and variable temperature (VT) 1H NMR. Our results reveal that in addition to Hydrogen bonding, cation conformational flexibility, functional group availability, cation–anion coordination strength and directionality of hydrogen bonds play key roles in governing the IL phase separation behavior. © 2017 Elsevier Inc. All rights reserved.

Temperature Dependence of Interfacial Bonding and Configuration Transition in Graphene/Hexagonal Boron Nitride Containing Grain Boundaries and Functional Groups.

The quasi-three-dimensional effect induced by functional groups (FGo) and the in-plane stress and structural deformation induced by grain boundaries (GBs) may produce more novel physical effects. These physical effects are particularly significant in high-temperature environments and are different from the behavior in bulk materials, so its physical mechanism is worth exploring. Considering the external field (strain and temperature field), the internal field (FGo and GBs) and the effect of distance between FGs and GBs on the bonding energy, configuration transition, and stress distribution of graphene/h-BN with FGo and GBs (GrO-BN-GBs) in the interface region were studied by molecular dynamics (MD). The results show that the regions linked by hydroxyl + epoxy groups gradually change from honeycomb to diamond-like structures as a result of a hybridization transition from sp2 to sp3. The built-in distortion stress field generated by the coupling effect of temperature and tension loading induces the local geometric buckling of two-dimensional materials, according the von Mises stresses and deflection theory. In addition, the internal (FGo and GBs) and external field (strain and temperature field) have a negative chain reaction on the mechanical properties of GrO-BN-GBs, and the negative chain reaction increases gradually with the increase in the distance between FGo and GBs. These physical effects are particularly obvious in high-temperature environments, and the behavior of physical effects in two-dimensional materials is different from that in bulk materials, so its physical mechanism is worth exploring.

Modeling of a bulk material stress state in a conical hopper hole under vibration action

A model of a fine-grained bulk material stress state in a conical hopper hole under vibration during material unloading is proposed. For the study, it is used a model of a discrete medium based on a balance of a small thickness elementary volume, in which the stress redistribution occurs by opening an outlet at the hopper bottom. A formula for determining the material radial stress in the discharge conical hopper hole is obtained, taking into account all force factors influencing the bulk material behavior. The influence of humidity, shape and geometric parameters of the hopper, and vibration intensity on the change of the bulk material stress state is investigated. As a result, the efficiency of vibration to improve the conditions of the fine-grained bulk material leakage from the hoppers is established.

On the forbidden graphene\u2019s ZO (out-of-plane optic) phononic band-analog vibrational modes in fullerenes

The study of nanostructures’ vibrational properties is at the core of nanoscience research. They are known to represent a fingerprint of the system as well as to hint the underlying nature of chemical bonds. In this work, we focus on addressing how the vibrational density of states (VDOS) of the carbon fullerene family (Cn: n = 20 → 720 atoms) evolves from the molecular to the bulk material (graphene) behavior using density functional theory. We find that the fullerene’s VDOS smoothly converges to the graphene characteristic line-shape, with the only noticeable discrepancy in the frequency range of the out-of-plane optic (ZO) phonon band. From a comparison of both systems we obtain as main results that: (1) The pentagonal faces in the fullerenes impede the existence of the analog of the high frequency graphene’s ZO phonons, (2) which in the context of phonons could be interpreted as a compression (by 43%) of the ZO phonon band by decreasing its maximum allowed radial-optic vibration frequency. And 3) as a result, the deviation of fullerene’s VDOS relative to graphene may hold important thermodynamical implications, such as larger heat capacities compared to graphene at room-temperature. These results provide insights that can be extrapolated to other nanostructures containing pentagonal rings or pentagonal defects.

Using magnetoelectric effect to reveal magnetization behavior of bulk and heavy ferromagnetic materials

Traditionally, magnetization performance of bulk ferromagnetic materials is evaluated mainly based on Faraday's law of electromagnetic induction, magneto-optical effect, Superconducting Quantum Interference Devices (SQUID, only for small specimen), etc. Here, we report that the magnetoelectric (ME) coupling effect from a composited Terfenol-D alloy/PMN-PT single crystal under a constant-amplitude AC magnetic field excitation (Hac = 0.25 Oe at 1 kHz) can be used to reveal magnetization behavior of an approaching bulk ferromagnetic material. Investigations show that the magnetostriction λ33,m, piezomagnetic coefficient d33,m, ME voltage (VME) response spectrum of the ME composite have a strong dependence on the external ferromagnetic material. It is further found that the required DC magnetic field for domain switching in Terfenol-D alloy could be notably decreased from hundreds Oe to only 10 Oe once a high-μ permalloy is approached. This work shows that the ME composite has the potential to quickly, qualitatively evaluate the magnetization (M) or permeability (μ) behavior of an approaching bulk and heavy ferromagnetic material or alloy via ME effect.

Design modification of iron ore bearing transfer chute using discrete element method

Purpose The dryer feed chute of the pellet plant plays an important role in the pelletizing process. The chute discharges sticky and moist iron ore fines (<1 mm) to the inline rotary dryer for further processing. Since the inception of the installation of the dryer feed chute, the poor flowability of the feed materials has caused severe problems such as blockages and excessive wear of chute liners. This leads to high maintenance costs and reduced lifetime of the liner materials. Constant housekeeping is needed for maintaining the chute and reliable operation. The purpose of this study is to redesign the dryer feed chute to overcome the above challenges. Design/methodology/approach The discrete element method (DEM) has been used to model the flow of cohesive materials through the transfer chute. Physical experiments have been performed to understand the most severe flow conditions. A DEM material model is also developed for replicating the worst-case material condition. After identifying the key problem areas, concept designs were proposed and simulated to assess the design improvements to increase the reliability of chute operation. Findings Flow simulations correlated well with the existing flow behavior of the iron ore fines inside the chute. The location of the problematic areas has been validated with that of the previously installed chute. Subsequently, design modifications have been proposed. This includes modification of deflector plate and change in slope and cross-section of the chute. DEM simulations and analysis were conducted after incorporating these design changes. A comparison in the average velocity of particle and force on chute wall shows a significant improvement using the proposed design. Originality/value Method to calibrate DEM material model was found to provide accurate prediction and modeling of the flow behavior of bulk material through the real transfer chute. DEM provided greater insight into the performance of the chute especially modeling cohesive materials. DEM is a valuable design tool to assist chute designers troubleshoot and verify chute designs. DEM provides a greater ability to model and assess chute wear. This technique can help in achieving a scientific understanding of the flow properties of bulk solids through transfer chute, hence eliminate challenges, ensuring reliable, uninterrupted and profitable plant operation. This paper strongly advocates the use of calibrated DEM methodology in designing bulk material handling equipment.

2D numerical simulation of auxetic metamaterials based on global DIC

This work discusses a novel approach to simulate metallic auxetic structures manufactured via Selective Laser Melting (SLM). SLMmanufactured metamaterials are difficult to simulate accurately based on nominal geometry and bulk material behaviour. The geometry after printing is different from the nominal CAD geometry. Artefacts due to the printing process such as pores yield a material behaviour which depends on the surface/volume ratio. We investigate a phenomenological approach to obtain a simulation model calibrated with experimental data and Digital Image Correlation (DIC). Finite Element based global DIC as suggested by Hild [1,2] allows for obtaining accurate displacement fields, consistent with the true deformation of the lattice structure. Based on the nominal CAD geometry, a simplified parametrized simulation model is created, exploiting the abundant symmetries of lattice structures. Using nodal displacements from DIC in combination with the expected forces from an experiment, the model is calibrated via LS-OPT. The approach is applied to an antitetrachiral, auxetic structure. Furthermore, we discuss the accuracy of the approach, its applicability to other structures and possible extension into 3D space.

Simulation of Uniaxial Compression for Flexible Fibers of Wheat Straw Using the Discrete Element Method

HighlightsSimulation of uniaxial compression was performed with flexible fibers modeled in DEM.Bond-specific DEM parameters were found to be sensitive in uniaxial compression.A calibration technique that is not plunger-dependent is shown and validated.Abstract. To accurately simulate a discrete element method (DEM) model, the material properties must be calibrated to reproduce bulk material behavior. In this study, a method was developed to calibrate DEM parameters for bulk fibrous materials using uniaxial compression. Wheat straw was cut to 100.2 mm lengths. A 227 mm diameter cylindrical container was loosely filled with the cut straw. The material was pre-compressed to 1 kPa. A plunger (50, 150, or 225 mm diameter) was then lowered onto the compressed straw at a rate of 15 mm s-1. This experimental procedure was simulated using a DEM model for different material properties to generate a simulated design of experiment (DOE). The simulated plunger had a travel rate of 40 mm s-1. The contact Young’s modulus, bond Young’s modulus, and particle-to-particle friction DEM parameters were found to be statistically significant in the prediction of normal forces on the plunger in the uniaxial compression test. The DEM calibration procedure was used to approximate the mean laboratory results of wheat straw compression with root mean square (RMS) percent errors of 3.77%, 3.02%, and 13.90% for the 50, 150, and 225 mm plungers, respectively. Keywords: Calibration, DEM, DOE, Flexible DEM particle, Uniaxial compression, Wheat straw.

Evaluation of bulk material behavior control method in technological units using DEM. Part 2

The research is dedicated to the development of special devices (capsules) that can be used to control the mining ore behavior in the technological unit in order to increase processes efficiency. In the first part of the article, the choice of the discrete element method for generating various particle trajectories in the unit (drum pelletizer) was substantiated. This part describes the specific technologies that were used to recognize the pelletizing mode. In particular, conversation of paths to sensor readings is implemented using the Matlab Sensor Fusion and Tracking Toolbox. The obtained readings were processed using two neural network classifiers (DNN and LSTM). As a result, stable models for recognizing the pelletizing modes of the unit were obtained. LSTM recognition accuracy is greater than DNN. The developed approach can be used to recognize the operating modes of other technological units. In addition, data on particles trajectories can be used to improve DEM models of technological processes. Future work consists of the capsule physical implementation and testing the recognition algorithm on a real unit.