Density Segregation Research Articles

Prediction of rod-like particle mixing in rotary drums by three machine learning methods based on DEM simulation data

The mixing of non-spherical particles in rotary drums exhibits significant complexity, particularly when density segregation and size segregation occur simultaneously. Three machine learning models: artificial neural network (ANN), extremely randomized trees (ERT), and particle swarm optimized support vector regression (PSO-SVR) were developed to predict the mixing time and mixing degree at the steady mixing state of rod-like particles in rotary drums. The training, validation, and test data for the machine learning models were generated from 121 discrete element method (DEM) simulations with four independent variables: revolution frequency, particle density ratio, particle size ratio, and drum length. All three models predicted the mixing degree accurately with R2≥ 0.94. The ERT and PSO-SVR models also predicted the mixing time well with R2≥ 0.88. Building machine learning models is hundreds of times faster than running DEM simulations, making these models highly promising for predicting larger-scale simulations with more complex-shaped particles.

Microstructure, mechanical properties, and deformation behaviour of LPBF 316L via post-heat treatment

ABSTRACT The study focused on analysing the changes in dislocation density and elemental segregation at cellular substructures, as well as the transformation of nano-oxide inclusions at different post-treatment temperatures, and their impacts on the strengthening mechanisms of 316L processed by laser powder bed fusion (LPBF). Additionally, through quasi in-situ tensile experiments, the plastic deformation and fracture behaviours of LPBF 316L after annealing at 900 °C were studied, revealing the reasons behind its high ductility. The results indicated that with increasing annealing temperatures, the nano-oxide inclusions coarsened and their density decreased due to the Ostwald ripening mechanism. The coarsened oxide particles act as barriers to moving dislocations and grain boundaries, thereby prolonging the recovery and recrystallization processes. This resulted in cellular substructures exhibiting high thermal stability. Consequently, the ultimate tensile strength of LPBF 316L after annealing at 900 °C is 651 MPa, with a total elongation of 62.3%, surpassing other studies.

Laser powder bed fusion of NbTi low-temperature superconductors

This study investigates the superconducting properties of additive manufactured in-situ NbTi alloy using laser powder bed fusion. Laser parameters were optimised for a maximum microstructural density and lowest Nb segregation fraction. These characters have been achieved at the sample built with an energy density of 3.33 J/mm2, where it shows a density value of 6.12 g/cm3, undissolved Nb fraction of 0.05 %, and randomly distributed equiaxed grains with an average size of 10–20 μm. Post-processing of the as-fabricated (AF) sample was explored as a route to collapse residual porosity and dissolve residual segregated Nb particles using hot isostatic pressing (HIP) and heat treatment, respectively. HIPing resulted in a decrease of the undissolved Nb particle fraction to 0.035 %. Heat treatment at 1250 °C for 24 h, followed by aging at 400 °C for 2 h, was found to result in the complete dissolution of Nb particles and precipitation of the ɑ-Ti phase that works as pinning centres to increase the superconducting properties. The grain size increased in both post-processes to 400–500 μm. Electrical and magnetic properties were also measured for the AF, HIP and heat-treated samples. The thermal variation of electrical resistivity showed a critical temperature (Tc) range of 9.8–9.0 K, 9.6–9.1 K and 9.9–8.8 K for the AF, HIP, and heat-treated samples, respectively, which were close to the values obtained from magnetic measurements. The critical current density (Jc) was calculated using Bean’s model employing the magnetic hysteresis loops. The AF condition showed a negligible value of Jc (5 × 10−3 kA/mm2), which improved to 0.28 kA/mm2 and 2.65 kA/mm2 for the HIPed, heat treated conditions, respectively (at 4.2 K, 5 T). Mechanical tensile testing was performed for the heat-treated sample to ensure both mechanical and superconducting properties would achieve the required performance, where achieves ultimate tensile strength value of 930 MPa, with 8 % elongation.

Study on particle size and density segregation law in the separating process of poor quality coal with high gangue content under the action of composite force field

ABSTRACT Thin-seam mining frequently captures a significant proportion of gangue and interbedded coal in surface coal mines. Consequently, raw coal has a broad range of particle size distributions and a high percentage of components with intermediate densities, which are complex and challenging to separate. This study aims to determine the method of product division and the segregation law of particle size and density of raw coal during the separation process using a vibration and airflow composite force field. A difference in the particle size segregation of the coal particles was evident. Particle-size segregation primarily occurs in the separation area. Large-particle-size coal has a wide distribution range, spreading over the entire bed and fully utilizing the bed to achieve separation. The material becomes increasingly displaced into the separation area as its particle size decreases, thereby weakening the separation effect. Large coal particles can undergo density segregation in the vertical direction, with low-density material placed in the upper layer. This ensures that low-density material is incorporated into the refined coal product. Regardless of density, the coal tended to tilt more toward the bottom layer as the particle size decreased. This results in a poor density stratification effect with refined coal products mixed with gangue and an increase in the mismatch content. The extent of fine coal discharge was determined to be two-fifths of the entire length of the discharge side. This ensures that the majority of refined coal is recovered and that there is no excessive gangue mixing with the refined coal output. Achieving a 55.54% yield, refined coal lowers its ash content by 16%, increases its calorific value by 1400 kcal/kg, and effectively separates coal with a high gangue concentration.

Ultrasound-enhanced separation characteristics of gas-solid fluidized bed for fine-grained fluorite ore

Due to the increasing mechanization of mining, there is an urgent need to develop dry separation technology for effective pre-enrichment of fine-grained fluorite ore and promote the efficient use of fluorite in arid or water-scarce areas. Therefore, we tried to enhance the separation performance of fine-grained fluorite ore by introducing ultrasound into the gas–solid separation fluidized bed. Fluidization test and high-speed dynamic image analysis were used to reveal the mechanism of density separation of two-component materials enhanced by ultrasound. The effects of gas velocity, static bed height, separation time and amplitude transformer diameter on density segregation of two-component materials were further studied. In addition, a gas–solid fluidized bed separation system under the action of ultrasound was established for the pre-enrichment of fluorite ore with different particle sizes. The study showed that the stability of the bed is improved by the introduction of ultrasound. And the separation efficiency was increased by 15.46% compared with ordinary fluidized bed. The possible deviation (E) values of 1–0.5 mm and 0.5–0.25 mm fluorite ore were 0.22 g/cm3 and 0.175 g/cm3 respectively. This study provides new insights into the separation of fine-grained fluorite ore by gas–solid fluidized bed under the action of ultrasound.

Abstract B076: Influence of residential segregation and women’s health provider density on advanced stage endometrial cancer diagnoses

Abstract Background. Endometrial cancer (EC) is the most common gynecologic malignancy in the US, with an increasing incidence. Non-Hispanic Black (NHB) women are disproportionately impacted by EC but the complex mechanisms by which this is occurring are not yet fully understood. Taking a social ecological approach to this issue, our objective was to determine if there are associations between county-level OB-GYN provider density and residential segregation as measured by the Index of Concentration at the Extremes (ICE) on late-stage EC diagnoses in Florida. Methods. All malignant EC cases were identified from 2001 to 2016 in the Florida Cancer Database System (FCDS). Using 5-year estimates from the 2013-2017 American Community Survey, five county-level ICE variables were calculated: economic (high vs low), race and/or ethnicity (non-Hispanic white (NHW) vs. NHB and NHW vs. Hispanic), and racialized economic segregation (low-income NHB vs. high-income NHW and low-income Hispanic vs. high-income NHW). County-level provider density was calculated as the number of OB-GYN providers divided by the female population of each county multiplied by 100,000. Early stage was defined as local and late stage was defined as regional/distant. Multivariable-adjusted logistic regression models were specified to estimate the association between each ICE variable and provider density separately on late-stage diagnosis of EC. Results. There were a total of 50,363 EC cases in Florida from 2001 to 2016 with 44,678 (88.7%) having stage information. Of those with stage information, the mean age at diagnosis was 64.1 years (SD: 11.9), 71.8% were NHW, 11.5% were NHB, 14.0% were Hispanic, and 2.8% were other race. The majority of individuals had government insurance (50.6%). More NHB women (27.1%) were diagnosed with aggressive EC histologies relative to NHW (16.4%) and Hispanic women (15.5%) (p<0.001). 14,366 (32.2%) were diagnosed with late-stage EC. A larger proportion of NHB women were diagnosed with later-stage EC compared to NHW women and Hispanic women (43.7% vs. 30.3% and 32.4%, respectively, p<0.001). NHB and Hispanic women had significantly greater odds of being diagnosed with later-stage EC compared to NHW women, regardless of residential segregation (OR: 1.46, 95% CI: 1.36, 1.56 and OR: 1.09, 95% CI: 1.01, 1.17, respectively). Women living in more economically disadvantaged Hispanic segregated counties had a greater odds of being diagnosed with later-stage EC compared to those living in more NHW segregated areas (OR: 1.16, 95% CI: 1.00, 1.65). Provider density was not found to be associated with later-stage diagnosis. Discussion. Advanced stage EC at diagnosis among Black and Hispanic women in Florida seems to be largely independent of provider density and residential segregation, though NHB more commonly present with metastatic disease. Biologic drivers of oncogenesis and barriers to timely care in this group require further exploration. Given the diversity and representation from Afro-Caribbeans in Florida, community-level investigations are required. Citation Format: Ashly Westrick, Zinzi Bailey, Matthew Schlumbrecht. Influence of residential segregation and women’s health provider density on advanced stage endometrial cancer diagnoses [abstract]. In: Proceedings of the 16th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2023 Sep 29-Oct 2;Orlando, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2023;32(12 Suppl):Abstract nr B076.

Rate controlling deformation mechanisms in SS316L stainless steel manufactured using laser powder bed fusion technique

We conducted uniaxial tensile strain rate jump tests to account for the strain rate controlling mechanisms in the additively manufactured SS316L stainless steel. Special emphasis is placed on the role of high dislocation density and chemical segregation on dictating the rate sensitive behavior. Lowest strain rate sensitivity is found, despite the highest dislocation density in the as build state, which signified the role of solute segregation at cell walls in increasing the activation volume and forms the strong basis for rejecting dislocation forest as the strain rate controlling obstacles. Consistent increase in the strain rate sensitivity with annealing is found consistent with the chemical homogenisation of the solutes causing smaller inter-obstacle spacing causing decreasing activation volume. Experimental findings are supported by CALPHAD simulations and mechanical threshold stress (MTS) modelling framework. Significant difference between the instantaneous and steady state rate sensitivity is understood using the dynamic pileup dislocation density readjustment mechanism causing considerable flow transient while adjusting the mobile dislocation density on strain rate change in the presence of solute decorated dislocation cells. Present investigation helps in gaining newer insights into the deformation mechanisms of the additively manufactured alloys featuring cellular microstructures.

Re-concentration of coking middling particles in a liquid-solid fluidized bed: Fluidization characteristics and density segregation

The re-enrichment of coking middling particles is an important way to realize the efficient utilization of coal resources. In this study, by combining numerical simulation and experimental method, the density segregation process and mechanism of coking middling particles in a liquid-solid fluidized bed are studied. The results show that the density segregation process of coking middling particles is mainly divided into the falling outer ring at the sidewall and the rising inner ring. Herein, the ash distribution variance of coking middling particles also shows a changing trend of first increasing and then decreasing with the values increase of operating parameter. Further, after the separation process in the fluidized bed, the cleaned coal product with a yield of 42.77 and an ash content of 8.69% is enriched from 1 to 3 mm coking middling coal (ash content of 28.2%), indicating that coking middling particles are separated efficiently in the liquid-solid fluidized bed.

Plastic deformation behavior and strengthening mechanism of SLM 316L reinforced by micro-TiC particles

In this work, the integrated study on the microstructure evolution, plastic deformation behavior, and strengthening mechanism of Selective Laser Melting (SLM) 316L austenitic stainless steel (ASS) reinforced with micro-TiC particles was investigated. The results indicated that there were lots of small angle grain boundaries in SLM 316L ASS, and the high dislocation density and component segregation of the cellular dislocation structure resulted in a good combination of high strength and good elongation in performance. The tensile strength, yield strength, and elongation of SLM 316L ASS were 682 MPa, 571 MPa, and 49.9%, respectively. The addition of TiC reinforced particles induced microstructure evolution, including grain refinement, reduction of epitaxial columnar dendrites, reduction of low angle grain boundary (LAGB) ratio and increase of Σ3 (60°/<111>) twin boundaries. Through the effects of grain refinement strengthening, Orowan strengthening, and dislocation strengthening, SLM 316L-2TiC showed a higher tensile strength of 1021 MPa and higher yield strength of 809 MPa, while maintaining an elongation of 30.8% due to the suppression of plasticity by twinning induced plasticity (TWIP) effect. Although nano-reinforced particles were commonly used to improve mechanical properties, in our work, we chose to add micrometer-sized TiC particles, and the strength of the SLM 316L-2TiC metallic matrix composites (MMCs) exceeded the previous reports of adding nanoparticles. The reason was that the small contact angle between TiC and 316L provides good wettability between the particles and the melt, and the selection of laser processing parameters ensures good bonding between TiC particles and the substrate.

Electroslag Hollow Ingots for Nuclear and Petrochemical Pressure Vessels and Pipes

The paper presents ground reasoning and results of experiments and modeling of heavy hollow ingot manufacturing using advanced electroslag technology. The requirements for ingots for huge diameter reactor pressure vessels include high density, homogeneity, and minimal segregation, which are very difficult to achieve by traditional casting. In the electroslag remelting process (ESR), hollow ingots form in between two copper water-cooled molds under effective heat removal. This improves the solidification pattern due to the shortening of a solidifying volume thickness more than twice compared with a solid ingot of the same diameter. The shallow liquid metal pool and narrow mushy zone at the ESR hollow ingot solidification assure their high metallurgical quality. Due to the dense and low segregation structure, ESR hollow ingots proved to be used for as-cast pipes and heavy wall billets for further forging. The results of a mathematical simulation within the range of simulated dimensions (the outer diameter up to 2900 mm, wall thickness up to 750 mm) also predict the favorable solidification pattern for thick-wall hollow ingots of big diameters. The analysis made and the modeling results provide a framework for scaling up the sizes of hollow ingots produced by ESR and widening their application for manufacturing heavy wall large diameter shells for nuclear and petrochemical industries. The higher reachable productivity of hollow ingot formation and lower capacity of power supply source than that for solid ingots of the same diameter and weight are also preconditions of their energy saving and cost-effective manufacturing.

Reverse to forward density segregation depending on gas inflow velocity in vibrated fluidized beds

Particle density segregations in vibrated fluidized beds depending on gas inflow velocity under the same vertical vibration condition are studied. Coarse-graining discrete element method and computational fluid dynamics numerical simulations are employed to capture the behaviors of reverse segregation in which heavy particles are located above light particles at zero gas inflow velocity or at velocities considerably lower than the minimum fluidization velocity of light particles. Furthermore, upon increasing the gas inflow velocity slightly, the forward segregation occurs, such that heavy particles are located below light particles. The mechanisms are also elucidated using the simulation results. Because of the relative motions between the particles and bed caused by vertical vibration, negative gauge pressure is observed to be dependent on the vibration phase. In the reverse segregation case, the accumulative effect of the downward gas pressure gradient force induced by vibration overcomes the upward force of the forced air flow. The wall friction transports both the heavy and light particles in the vicinity of the sidewall to the bed bottom, where the local void fraction is comparatively high and reverse segregation mainly occurs. Reverse segregation results from the combined effects of the downward gas pressure gradient force, particle transport, and local formation of the high void region. The increase in gas inflow velocity enhances the upward pressure gradient force, resulting in forward segregation.

Particle force-based density segregation theory for multi-component granular mixtures in a periodic chute flow

Density segregation of multi-component granular mixtures in a dense, gravity-driven flow over a rough and bumpy periodic chute surface is studied using theory and simulations. An existing theoretical model for predicting the steady-state concentration field of each species in a binary mixture using the forces acting on the particles is generalised for multi-component mixtures in this work. In addition, the rheological model for binary mixtures is also extended to multi-component mixtures. In contrast to the percolation velocity-based empirical segregation models that do not account for the rheology and need prior knowledge of the velocity field, the present approach accounts for the inter-coupling of rheology with segregation. The momentum balance equations are solved, along with the mixture rheological model as well as the multi-component density segregation model, to obtain concentration fields using an iterative numerical method. The theoretical predictions are compared with discrete element method (DEM) simulations for ternary, quaternary and quinary granular mixtures differing in density. The steady-state profiles for the concentration of different species as well as other flow properties predicted from the theory are in excellent agreement with the DEM simulation results for a variety of compositions over a range of inclination angles for different density ratios. Through this work, we take the first essential step towards proposing a generalised particle force-based segregation theory for multi-component mixtures differing in size and/or density.

Temperature effect on radiation‐induced dislocation loops in a FCC high purity CrFeMnNi multi‐principal element alloy

Temperature effect on dislocation loop density and radiation-induced segregation (RIS) phenomena are investigated on an ion irradiated 15Cr-46Fe-17Mn-22Ni (at.%) multi-principal element alloy (MPEA) over a wide range of temperatures. From 95 K to 623 K, loop densities are temperature independent and close to ∼5.0 × 1022 m-3. Above 623 K, loop densities decrease until ∼1.05 × 1021 m-3 at 823 K. This tendency is the same as in the conventional ternary Fe-Cr-Ni alloys. Besides, Ni enrichment and Cr, Fe, Mn depletion on loops are observed at 823 K by scanning transmission electron microscopy coupled to energy dispersive X-ray spectroscopy and atom probe tomography with comparable RIS amplitude. This solute redistribution is explained by an inverse Kirkendall (IK) mechanism. In contrast, no obvious chemical segregation/depletion phenomena are detected at 298 K, which reveals the temperature dependence of the IK effect. This comprehensive study of loop behavior as a function of temperature gives a better understanding of CrFeMnNi MPEAs under irradiation.

Numerical Simulation of Density Segregation of Al Alloy During Centrifugal Casting

The centrifugal casting process of 6082 Al alloy was simulated by ANSYS Fluent software. The effect of rotation speed on the flow field and the degree of density segregation of Mg2Si particles was analysed. The linear velocity of the molten metal increased as the rotational speed increased. The Discrete Phase Model was used to track the movement of the particles. In centrifugal casting, the Mg2Si with low density is segregated toward the inner wall of the casting. As the rotation speed increased, the thickness of the enriched layer decreased, but the mass fraction in enriched layer increased, and the degree of segregation intensified.

Understanding centrifugal casting in the manufacture of functionally graded materials

Centrifugal casting is a shaping technique intended for ceramic tubular structure manufacture, where the particle size and density are exploited to produce asymmetrical membranes and functionally graded materials. However, some well-established insights about particle segregation are debatable and remain unclear. For instance, small particles do not necessarily stay in the inner region, and the bigger particles do not accumulate in the outer. Herein several manufacturing parameters were studied through Taguchi’s robust design, using discrete element method-based simulations to generate the data. Alumina powder was used as model material and water as the liquid phase, to assess the green cast formation time, the cast thickness, the roundness, the changes in relative density, and particle size distribution along the cast’s cross-section. The mean particle diameter and the rotation speed are the most influential parameters for the casting time. The volume fraction of solids on the precursor slurry is decisive regarding the cast structural properties, and particle segregation is negligible, except for size differences above one order of magnitude. When a fraction of denser nickel powder was added, density segregation was also observed, but the size differences can overshadow its effect. In addition, alumina and nickel particles were cast in a lab-scale centrifuge and experimentally validated the segregation of particles. The centrifugal casting method was successfully applied for producing the Al2O3-Ni composites with a gradient distribution of the Ni phase.

Insight on the correlation between micro-region structural characteristic and corrosion behavior of dilute Mg-0.5Bi-0.5Sn-0.5In alloy

This study focuses on the influence of micro-region structural characteristic on the corrosion behavior of the dilute extruded Mg-0.5Bi-0.5Sn-0.5In alloy. The results indicate that the corrosion mode can be determined by the presence of local crystallographic defects. In addition, the long-term corrosion rate is mainly controlled by the grain orientation variation in different regions. This is mainly attributed to the following two factors: (i) The higher area fraction of basal oriented grains, which in turn leads to the reduction of cathodic current density, the increment of corrosion potential, and the decrement of overall surface energy. (ii) The homogeneous microstructure with lower dislocation density and solute segregation degree, which results in dominated filiform corrosion mode and the formation of protective corrosion product film.

Conversion air velocity at which reverse density segregation converts to normal density segregation in a vibrated fluidized bed of binary particulate mixtures

It is well known, when binary mixtures of different-density particles of the same size are vertically vibrated or fluidized by airflow through the bottom, the particles segregate by density. Reverse density segregation occurs in the vibrated bed; heavier particles move upward and lighter ones move downward, and normal density segregation occurs in the fluidized bed; lighter particles move upward and the heavier ones move downward. In this study, we investigated the particles’ behavior in a vertically vibrated fluidized bed at various air velocity using two types of particulate mixtures of glass beads (GB) and stainless steel powder (SP) or iron powder (IP) of same size. We found that reverse segregation converts to normal segregation at a certain air velocity; here we call it “conversion air velocity”. Then, we investigated the likely origin of the conversion air velocity considering the minimum fluidization air velocity umf determined for the three monocomponent particles (GB, SP and IP) with and without vibration. We found that the conversion air velocity is close to the umf of the lower density particles (GB) with vibration, indicating that the conversion from reverse segregation to normal segregation occurs around umf of lighter particles with vibration.

Nano-scale heterogeneity-driven metastability engineering in ferrous medium-entropy alloy induced by additive manufacturing

Selective laser melting (SLM) offers unprecedented advantages in fabrication of metals and alloys with complex geometry and unique microstructural features with hierarchical heterogeneity. The SLM process also induces a unique cell structure with high dislocation density and solute segregation at cell boundaries. Here, we propose an innovative utilization of unique dislocation network to achieve superior mechanical properties through metastability engineering of ferrous-medium entropy alloy (FeMEA). While the high dislocation density at cell boundaries contributes to the improvement of yield strength as additional barriers of dislocation movement, the solute segregation at cell boundaries can beneficially control the phase instability of matrix in materials produced by SLM. Our results demonstrate that solute segregation at cell boundaries decreases the face-centered cubic phase stability in the matrix and activates transition of the deformation mechanism from slip to metastable plasticity (i.e., transformation-induced plasticity). Furthermore, the high density of dislocation at cell boundaries also has an effect on not only yield strength enhancement but also controlling kinetics of metastable plasticity, and it beneficially contributes the high ductility of the SLM-processed FeMEA. This work presents a new microstructural design strategy for beneficially customizing the material performance of high-quality products based on SLM-driven metastability engineering of metallic materials.

Numerical Investigation of Density Segregation on a Shaking Table Using the Discrete Element Method

Numerical Investigation of Density Segregation on a Shaking Table Using the Discrete Element Method

Density and size-induced mixing and segregation in the FT4 powder rheometer: An experimental and numerical investigation

Segregation of granular materials is often induced by differences in size, density, shape and surface properties. Density and size-induced mixing and segregation of binary mixtures of glass beads and/or resin particles in the FT4 powder rheometer are investigated experimentally using a new FT4 methodology. The proposed methodology allows for quantification of mixing and segregation of components based on a mixing index. It is observed that the mixing index increases with increasing density and size ratio. Variation of flow energy and torque is related to the mixing and segregation of the mixture components, thus demonstrating that the FT4 powder rheometer may be used as a predictive tool for the tendency of mixture components to segregate under various stress conditions. Numerical analysis by DEM shows that for non-cohesive systems mixing and segregation occur by sifting of fines through interstitial gaps formed between coarse particles in the dilated region. For the non-cohesive system, higher blade tip speeds reduce the rate of mixing and minimise the segregation of different-sized components. Increasing the interfacial energy reduces the rate of mixing and alleviates the segregation of particles. For the cohesive systems, mixing occurs by rupture of cohesive fine clusters with the mixing index increasing with increasing blade tip speed owing to the higher shear stresses that break the agglomerates.