Rigid Particles Research Articles

Elastic reinforcement and yielding of starch-filled lipid gels

Many foods involve complex suspensions of assorted particles in a Newtonian liquid or viscoelastic medium. In this work, we study the case of suspensions of non-Brownian non-interacting rigid particles: starch, embedded in a soft solid: a colloidal lipid gel. We relate the macroscopic properties of the suspensions to the mechanics of the colloidal gel and the particle volume fraction. As particle volume fraction increases, the suspension gradually stiffens and becomes brittle as the system approaches its maximum packing fraction. The latter is independently determined from a geometric theory of random close packing for polydisperse hard spheres based on the log normal distribution of starch particles dispersed in oil. The elastic modulus, yield stress and yield strain are interrelated through simple scaling laws from a micromechanical homogenization analysis of hard spheres isotropically-distributed in yield stress fluids. • The rheology of non-Brownian non-interacting starch particles filling a viscoelastic colloidal lipid gel was investigated. • As starch volume fraction increases the suspension stiffens, turns brittle as it approaches its maximum packing fraction. • The maximum packing fraction is determined from a geometric theory of random close packing for polydisperse hard spheres. • Linear and nonlinear rheology are interrelated through simple scaling laws from a homogenization micromechanical analysis.

Pair interactions between viscous drops in a viscoelastic matrix in free shear: Transition from passing to tumbling trajectories

Shear-induced pair interactions between viscous drops suspended in a viscoelastic matrix are numerically investigated examining the effects of elasticity and drop deformability on their post-collision trajectory. Two different trajectory types are identified depending on the Weissenberg number Wi and capillary number Ca. Drops suspended in a Newtonian matrix (Wi = 0.0) show a passing trajectory where drops slide past each other and separate in the stream-wise direction. However, when increasing the Weissenberg number above a critical value, a tumbling/doublet trajectory is observed where two drops rotate around the midpoint of the line joining their centers, as was also seen previously for rigid particles. The tumbling trajectory is explained by investigating the flow around a single drop in shear. Elasticity generates a larger region of spiraling streamlines around a drop, which, during a pair interaction, traps the second drop giving rise to the tumbling pair. Decreasing deformability (lower Ca) and increasing viscoelasticity (higher Wi) favor a tumbling trajectory. With simulations sweeping the parameter space, we obtain a phase plot of the two different trajectories as functions of Ca and Wi. Treating the tension along the curved streamlines due to the non-zero first normal stress difference in the viscoelastic medium as an enhancement to the interfacial tension, we have developed an approximate force balance model for the zone of spiraling streamlines. It qualitatively captures the observed scaling of the critical Ca and Wi values at the phase boundary. The effects of unequal size, initial configuration, and non-unity viscosity ratio are briefly investigated.

Effect of roughness on elongated particles in turbulent channel flow

In this paper, we examine the deposition and resuspension of rigid elongated particles transported by turbulence in a channel bounded by two-dimensional roughness. To analyze these processes, we use an Euler–Lagrange approach based on Direct Numerical Simulation of the carrier phase and Lagrangian Particle Tracking of the dispersed phase. Four different channel configurations are considered: One is the classical channel flow bounded by smooth flat walls, whereas the other three correspond to a channel with walls of increasing roughness. The roughness shape is obtained by superimposition of sinusoidal functions with different amplitude k and is characterized by the mean absolute value of the amplitude, k̄= 0.012, 0.024 and 0.050 (k̄= 0 for a smooth wall). The friction Reynolds number is Reτ=150 for all cases. Particles are modeled as prolate ellipsoids and classified according to their aspect ratio λ. Three different particles sets are considered: λ=1, corresponding to the reference case of spheres, λ=3, corresponding to slightly elongated particles, and λ=10, corresponding to long fiber-like particles. The particle response time is St+=5 for all sets. In turbulent flow bounded by smooth walls, particles are known to accumulate preferentially in the near-wall region, leaving the central region of the channel scarcely populated. Wall roughness produces a completely different scenario: Particles exhibit a more homogeneous distribution along the wall-normal direction. We show that the aspect ratio does not affect the preferential distribution and the velocity statistics of the particles. The effect of elongation, however, becomes important for their preferential orientation, which is much weaker than in the smooth-walls case, in the near-wall region, while recovering the smooth-walls case in the outer region of the channel. This finding supports the validity of Townsend’s similarity hypothesis, namely that the bulk flow dynamics are unaffected by the roughening of the bounding walls.

Neutron Tomography Studies of Two Lamprophyre Dike Samples: 3D Data Analysis for the Characterization of Rock Fabric

The rock fabric of two lamprophyre dike samples from the Koy-Tash granitoid intrusion (Koy-Tash, Jizzakh region, Uzbekistan) has been studied, using the neutron tomography method. We have performed virtual segmentation of the reconstructed 3D model of the tabular igneous intrusion and the corresponding determination of dike margins orientation. Spatial distributions of inclusions in the dike volume, as well as further analysis of size distributions and shape orientations of inclusions, have been obtained. The observed shape preferred orientations of inclusions as evidence of the magma flow-related fabric. The obtained structural data have been discussed in the frame of the models of rigid particle motion and the straining of vesicles in a moving viscous fluid.

Effective viscosity of random suspensions without uniform separation

This work is devoted to the definition and the analysis of the effective viscosity associated with a random suspension of small rigid particles in a steady Stokes fluid. While previous works on the topic have conveniently assumed that particles are uniformly separated, we relax this restrictive assumption in the form of mild moment bounds on interparticle distances.

Ultrasound-assisted dispersion of TiB2 nanoparticles in 7075 matrix hybrid composites

Refinement and dispersion of rigid ceramic particles enhance the mechanical properties of particulate reinforced aluminum matrix composites (PRAMCs). However, nanoparticles are intrinsically clustered or agglomerated together in melts and thereby reduce their strengthening efficacy. Ultrasound cavitation and acoustic streaming can effectively improve the distribution of nanoparticles in melts. In this work, we use synchrotron radiation X-ray computed tomography (SR-CT) to unveil the particle dispersion mechanism by ultrasound vibration treatment (UVT) from three-dimensional perspective. The SR-CT results indicated that the mesoscale agglomerates in a high-strength 7075 aluminum alloys can be eliminated completely upon UVT. Two types of TiB2 particles have been identified, termed as micro-size TiB2 particles (MTPs) and nano-size TiB2 particles (NTPs), which were observed to be aggregated along the grain boundaries and dispersed uniformly within the α-Al grains, respectively. Tensile tests reveal significant strengthening of the composites in the as-cast state, suggesting effective Orowan strengthening. This strength enhancement is attributed to the dispersed NTPs that have been retained after solidification. It is also inspiring to see the concurrent increase in the ductility of the composites after UVT, thanks to the improvement in particle distribution.

In-situ construction of particle-accumulated hydrophobic packing layer from rigid polyurethane wastes for gas pre-dehydration

HypothesisRigid polyurethane, a common insulation material, is difficult to degrade naturally and poses significant health and environmental risk. Consequently, the cost-effective and efficient reuse of these solid wastes is a great challenge. ExperimentsHerein, we report an in-situ construction of hexadecyltrimethoxysilane (HDTMS) hydrophobic films on rigid polyurethane waste particle (RPUWP) as an accumulated packing layer in the gas-liquid pre-separator for gas pre-dehydration. FindingsThe RPUWP grafted with HDTMS (P-HDTMS) packing layer exhibits excellent hydrophobicity in the air, acid (pH = 1), alkali (pH = 14), and high-temperature (over 95 ℃) resistance. Also, the gas pre-dehydration performance of the accumulated P-HDTMS packing layer in the gas-liquid pre-separator was evaluated by the water dew point depression (ΔTd). It is worth mentioning that the accumulated packing layer can stabilize and greatly reduce the ΔTd by 17.8 ℃ in over 48-hour uninterrupted operation through the coalescence separation mechanism. Therefore, the low-cost accumulated P-HDTMS packing layer is expected to be an ideal candidate material for gas pre-dehydration in large-scale practical applications. This work not only provides a novel method for the resource utilization of plastic solid wastes but also provides a hitherto unexplored perspective for gas dehydration in industrial production.

A breakable grain-based model for bi-modular rocks

This article proposes a breakable grain scheme and a method to achieve bi-modular elastic material behavior in grain-based models of rocks using the Hybrid Lattice/Discrete Element Method; a version of the Discrete Element Method that employs Rigid Body Spring Network interactions. First, the paper presents both contributions and two validation exercises regarding bi-modular elastic behavior. Subsequently, a set of comprehensive parametric analyses defines the impact that numerical input parameters have on macroscale results, including: crack initiation and damage stresses; unconfined compression and direct tensile strengths ; and material’s characteristic length. Of note, the analyses investigate the influence of heterogeneity, based on the application of the Weibull probability distribution to compressive and tensile Young moduli and inter and intragranular strength parameters. Afterwards, simulations based on three theoretical rock types show the capabilities of the Hybrid LDEM with the proposed contributions in representing typical macroscale properties of rocks observed in laboratory tests. Lastly, visual comparisons between grain breakage processes from numerical simulations and laboratory thin-section analyses indicate consistent correspondence, which evidences the potential application of the developed methods to future research focused on rocks’ microcracking phenomena. This work concludes that the proposed breakable grains and bi-modular material behavior schemes widen the range of macroscale properties that grain-based models can produce while preserving simplicity. • A novel breakable grain-based model is proposed for bi-modular rocks. • The model is based on the Hybrid Lattice/Discrete Element Method. • Breakable grain approach operates by effectively slicing the rigid particles. • Bi-modular elastic behavior is realized by a fictitious stress scheme. • The methods widen the range of macroscale properties that grain-based models produce.

Annealing‐induced high impact toughness of immiscible isotactic polypropylene/poly(acrylonitrile‐butadiene‐styrene) blend

AbstractIn present work, acrylonitrile‐butadiene‐styrene graft copolymer (ABS) with dual roles of macromolecular β nucleating agent and organic rigid particles was introduced into isotactic polypropylene (iPP) via melt blending, and the iPP/ABS blend samples were further annealed at moderate temperature (120–140°C) for 3 h. The corresponding microstructural evolution of pure iPP and ABS‐toughened iPP upon annealing was analyzed with differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM) in detail. The results showed that the introduction of ABS and further annealing treatment have synergistic toughening effect on iPP. For the iPP with the addition of 4 wt% ABS, the impact strength is increased by 77%. After annealing at 130°C for 3 h, the impact strength of iPP alone is 72% higher than that of its unannealed counterpart, while this value is increased remarkably by 258% for the iPP/ABS blend. The remarkably elevated impact toughness of iPP blended with ABS upon annealing could be ascribed to favorable heterogeneous nucleation effect of ABS, promoted mobility of chain segments in the amorphous region of iPP, and enhanced interfacial interaction between the iPP and ABS upon annealing.

Numerical investigation of the formation and stability of homogeneous pairs of soft particles in inertial microfluidics.

We investigate the formation and stability of a pair of identical soft capsules in channel flow under mild inertia. We employ a combination of the lattice Boltzmann, finite element and immersed boundary methods to simulate the elastic particles in flow. Validation tests show excellent agreement with numerical results obtained by other research groups. Our results reveal new trajectory types that have not been observed for pairs of rigid particles. While particle softness increases the likelihood of a stable pair forming, the pair stability is determined by the lateral position of the particles. A key finding is that stabilisation of the axial distance occurs after lateral migration of the particles. During the later phase of pair formation, particles undergo damped oscillations that are independent of initial conditions. These damped oscillations are driven by a strong hydrodynamic coupling of the particle dynamics, particle inertia and viscous dissipation. While the frequency and damping coefficient of the oscillations depend on particle softness, the pair formation time is largely determined by the initial particle positions: the time to form a stable pair grows exponentially with the initial axial distance. Our results demonstrate that particle softness has a strong impact on the behaviour of particle pairs. The findings could have significant ramifications for microfluidic applications where a constant and reliable axial distance between particles is required, such as flow cytometry.

How do the finite-size particles modify the drag in Taylor–Couette turbulent flow

We experimentally investigate the drag modification by neutrally buoyant finite-size particles with various aspect ratios in a Taylor–Couette (TC) turbulent flow. The current Reynolds number, $Re$ , ranges from $6.5\times 10^3$ to $2.6\times 10^4$ , and the particle volume fraction, $\varPhi$ , is up to $10\,\%$ . Particles with three kinds of aspect ratio, $\lambda$ , are used: $\lambda =1/3$ (oblate), $\lambda =1$ (spherical) and $\lambda =3$ (prolate). Unlike the case of bubbly TC flow (van Gils et al., J. Fluid Mech., vol. 722, 2013, pp. 317–347; Verschoof et al., Phys. Rev. Lett., vol. 117, issue 10, 2016, p. 104502), we find that the suspended finite-size particles increase the drag of the TC system regardless of their aspect ratios. The overall drag of the system increases with increasing $Re$ , which is consistent with the literature. In addition, the normalized friction coefficient, $c_{f,\varPhi }/c_{f,\varPhi =0}$ , decreases with increasing $Re$ , the reason could be that in the current low volume fractions the turbulent stress becomes dominant at higher $Re$ . The particle distributions along the radial direction of the system are obtained by performing optical measurements at $\varPhi =0.5\,\%$ and $\varPhi = 2\,\%$ . As $Re$ increases, the particles distribute more evenly in the entire system, which results from both the greater turbulence intensity and the more pronounced finite-size effects of the particles at higher $Re$ . Moreover, it is found that the variation of the particle aspect ratios leads to different particle collective effects. The suspended spherical particles, which tend to cluster near the walls and form a particle layer, significantly affect the boundary layer and result in maximum drag modification. The minimal drag modification is found in the oblate case, where the particles preferentially cluster in the bulk region, and, thus, the particle layer is absent. Based on the optical measurement results, it can be concluded that, in the low volume fraction ranges ( $\varPhi =0.5\,\%$ and $\varPhi = 2\,\%$ here), the larger drag modification is connected to the near-wall particle clustering. The present findings suggest that the particle shape plays a significant role in drag modification, and the collective behaviours of rigid particles provide clues to understand the bubbly drag reduction.

Comparative numerical study of pneumatic conveying of flexible elongated particles through a pipe bend by DEM-CFD

Pneumatic conveying is widely used for the transportation of granular materials, where the flow of a gas is used to drive particles along pipes. While many granular materials comprise of compact and regularly shaped particles, this study aims for the numerical analysis of transport of biomass particles, which are predominantly non-spherical, frequently fiber-like and flexible and yet not broadly addressed. The Discrete Element Method coupled with Computational Fluid Dynamics (DEM-CFD) using a local volume-averaging technique is used as a tool to analyze pneumatic conveying of flexible biomass particles focusing on a pipe bend as relevant domain. The required particle flexibility is incorporated into the DEM by using a bonded particle model. Two different damping coefficients instead of just one are suggested to be used to ensure the same damping ratio at different fiber deformations. A simple technique relying on a smoothing coefficient for the damping forces and moments is proposed to minimize fluctuations and to allow the increase of the used time step in the DEM-CFD simulations. Laboratory tests with wheat straw were performed to determine its mechanical and physical properties. Thereon effects of the particle stiffness, the bond damping, the particle mass flow rate, the particle length and the gas inflow velocity on pneumatic particle transport are numerically analyzed. Obtained results demonstrate that particle trajectories in the vertical pipe section and the pressure drop depend on the particle stiffness. However, the performed comparison with the results obtained using rigid, non-flexible particles suggests that pneumatic conveying of more stiff particles can be achieved by relying on rigid particles without flexible bonds. Additionally, the performed tests using different bond damping values demonstrate the importance of the considered damping ratio for the outcome of the simulations.

Investigation of the impact of a particle foam insulation on frost buildup on the aircraft structure

The aircraft insulation separates the thermally comfortable cabin interior environment from the extremely cold outside condition. However, the fabrication and installation of the insulation in the aircraft is a labour intensive task. Tailored, rigid particle foam parts could be a solution to speed up installation process. The presented study investigates the feasibility of such a concept from a hygrothermal point of view. Due to the temperature difference between the cold air trapped between aircraft skin and insulation on one side and the warm cabin air on the other side, a buoyancy induced pressure difference forms. This effect drives the warmer air through leakages in the insulation system towards the cold skin. Here, moisture contained in the air condenses on the cold surfaces, increasing the risk for uncontrolled dripping (“rain in the plane”) when it melts. Therefore, this study compares the frost build-up of different installations of a rigid particle foam frame insulation with the classical glass fiber capstrip. Tests are hosted in the Fraunhofer Lining and Insulation Test Environment chamber.

A note on the motion of a rigid circular particle buried in an elastic solid

A note on the motion of a rigid circular particle buried in an elastic solid

Differences of Pore Features in Marine Shales between Lower Cambrian and Lower Silurian Formations of Upper Yangtze Area, South China

Lower Cambrian shale and lower Silurian shale are both typical of oil-prone kerogen and siliceous composition, but different in thermal maturities. Porosity differences were determined in marine shales between the two shales. Measurements were utilized including organic geochemistry, XRD, scanning electron microscopy (SEM) and N2 gas adsorption. Pore volume (PV) of lower Silurian shale was approximately 1.5 times higher than that of lower Cambrian shale, and pore surface area (PSA) of lower Silurian shale was almost 2.5 times higher than that of lower Cambrian shale. Lower Cambrian shale and lower Silurian shale possess similar materials, but distinctive thermal degrees. Evolution mechanisms of different types of pores, especially organic matter (OM)-hosted pores, may trigger this different pore features. Pores of rigid framework are the residue of primary interparticle pores during the burial history. Pores associated with clay flakes can be preserved well adjacent to rigid grains or secondary minerals acting as rigid frameworks or grain supporters. Dissolved pores in both lower Cambrian shale and lower Silurian shale barely contribute to the total porosity and mean little to the permeability. Both excessive OM content and over thermal maturity are detrimental to development of OM-hosted pores. Rigid particles, clay flakes, and OM commonly co-exist within shale matrix. Rigid grains act as supporters, clay flakes confine ample space, and OM first migrates into and provides secondary OM-hosted pores. In this condition, pores can be preserved owing to associating matrix with good mechanic and chemical stability. The significant differences of structural settings result into various hydrocarbon explosion efficiency and different pressure circumstance, which consequently leads to the different pore features between the two shales. For lower Cambrian shale, overpressure circumstance diminish if hydrocarbon expels outside of the shale system, and OM-hosted pores destroy through compaction. Sustaining overpressure and abundant residue hydrocarbon (migrated OM) make positive contributions to the pore properties, in terms of numbers, diameters and connectivity of the lower Silurian shale samples.

Quality evaluation of glutenite reservoirs of intergranular - secondary dissolution pore type using a quantitative method

Glutenite (coarse-grained clastic) reservoirs of intergranular–secondary dissolution pore type are dominated by residual intergranular pores and secondary dissolution pores, and characterized by low porosity, low permeability, strong heterogeneity, and highly variable physical properties. It is difficult to conduct a quantitative quality assessment of these reservoirs while their primary control factors remain unclear. In this paper, experimental core data and drilling, logging and seismic data are used to assess the effect of sedimentary facies on reservoir quality. Favorable sedimentary facies zones are identified by analyzing the characteristics of glutenite reservoirs, which includes investigating rock components and their effects on reservoir quality. Argillaceous matrix content and rigid particle content are identified as the primary control factors for these reservoirs. Logging curves sensitive to reservoir quality are selected and examined to continuously characterize the physical parameters of the reservoirs. It establishes a calculation model of reservoir assessment parameters through multivariate regression and determines the quantitative assessment parameter Fr. The quality of the glutenite reservoirs is defined using conventional logging curves. This study also predicts the plane distribution of high-quality reservoirs through geostatistical inversion of the reservoir assessment parameters based on conventional wave impedance inversion, thus providing insight and guidance for quantitative assessment and quality prediction of glutenite reservoirs of the intergranular-secondary dissolution pore type. The application of this method to well deployment based on qualitative evaluation of the glutenite reservoirs in oilfields yielded favorable results.

A green way to simultaneously enhance the mechanical, flame retardant and anti-ultraviolet aging properties of polylactide composites by the incorporation of tannic acid derivatives

Polylactic acid (PLA), characterized by its biodegradability, easy processing, and environmental friendliness, is regarded as one of the ideal substitutes for petroleum-based polymers. But, the flammability and UV light sensitivity of PLA often impact the safety and service life of its products. In this study, a bio-based additive (BA-TA-MEL) is synthesized via a one-pot method and used as a flame-retardant and anti-UV agent for PLA. The results show that PLA/5%BA-TA-MEL can achieve the desired V-0 degrade in the UL-94 test and an LOI value of 27.1%. Moreover, the PLA/5%BA-TA-MEL exhibits brilliant UV resistance, which increases the UPF to 290.4 from 0.4 of pure PLA. The BA-TA-MEL acts as a rigid particle in the matrix, effectively enhancing the tensile strength of materials. The current work develops a new approach to preparing biodegradable material with excellent performance and extended life to reduce the environmental pressure and pollution caused by petroleum-based plastics.

Damage analysis of a CFRP cross-ply laminate subjected to abrasive water jet cutting

The abrasive water jet (AWJ) cutting technique is one of the promising techniques used in machining of composite materials due to lack of thermal damage, lower tool wear and higher productivity. In this study, the AWJ cutting of a cross-ply CFRP laminate was investigated experimentally and numerically. The purpose is to understand the underlying physics of the AWJ cutting of a composite plate, which can be later used to control the process as well as optimizing its parameters. In the performed tests of the plate with a stacking sequence of [0°/90°/0°/90°] and having a total thickness value of 0.84 mm, where the pressure of particles and impact angle were varied, different failure characteristics such as fiber pull-out, fiber breakage, fiber debonding, matrix cracking and delamination were noticed. A three-dimensional FE model of the process was developed using ABAQUS finite element software to understand the underlying physics. In the model, the pure water jet particles following the linear Hugoniot form of the Mie-Grüneisen equation of state and highly rigid abrasive particles were modelled using smooth particle hydrodynamics. While the three dimensional Hashin damage model was used to simulate the intra ply damage, cohesive zone elements were used to predict the delamination. The damage characteristics in the composite plate was investigated for different process parameters. When the speed of the AWJ particles increased from 300 m/s to 600 m/s, the amount of delamination decreased from 6.44% to 5.69% at the top interface with no more delamination observed at the middle and bottom interfaces. The delamination performance of 0°/90°/0°/90° orientation was found to be better than those of 0°/90°/90°/0° and 0°/0°/90°/90° orientations. The impact angle of the particles affected the material removal rate in the process significantly. The failure behaviour of the laminate subjected to AWJ and pure water jet cuttings (PWJ) were also compared.

Effect of packing conditions and materials properties on loose packing fraction of rigid particles: a theoretical and experimental review

This paper focuses on the effect of packing conditions and materials properties on loose packing fraction of particles from theoretical and experimental perspectives. First, the difference in loose packing of particles was measured in different conditions. In the second part, we obtained the main factor that dominated the loose packing fraction in different particle scales. We concluded that kinetics energy induced by the gravitational potential energy almost has no influence on the loose packing fraction for particles smaller than a few millimeters. On the contrary, the wall effect became more and more evident with the increase of particle size. Particle morphology and PSD significantly affect the loose packing of particles above the sub-millimeter size. Moreover, for micron-sized particles, the Van der Waals force was shown to dominate all other colloidal interactions, and the ratio between Van der Waals force and effective gravity determined the loose packing fraction of fine powders.

Sedimentation of random suspensions and the effect of hyperuniformity

This work is concerned with the mathematical analysis of the bulk rheology of random suspensions of rigid particles settling under gravity in viscous fluids. Each particle generates a fluid flow that in turn acts on other particles and hinders their settling. In an equilibrium perspective, for a given ensemble of particle positions, we analyze both the associated mean settling speed and the velocity fluctuations of individual particles. In the 1970s, Batchelor gave a proper definition of the mean settling speed, a 60-year-old open problem in physics, based on the appropriate renormalization of long-range particle contributions. In the 1980s, a celebrated formal calculation by Caflisch and Luke suggested that velocity fluctuations in dimension $$d=3$$ should diverge with the size of the sedimentation tank, contradicting both intuition and experimental observations. The role of long-range self-organization of suspended particles in form of hyperuniformity was later put forward to explain additional screening of this divergence in steady-state observations. In the present contribution, we develop the first rigorous theory that allows to justify all these formal calculations of the physics literature.