Increase In Packing Density Research Articles

Comparative evaluation of accuracy in near-infrared and Raman spectroscopic determinations of component concentration in packed solid mixtures under various packing densities

BackgroundPhysical characteristics of packed samples, such as packing density, influence subsequent near-infrared (NIR) and Raman spectral features. This potential decrease in accuracy is a concerning issue in practical applications, such as the analysis of pharmaceutical tablets using vibrational spectroscopy. Thus, we compared the accuracy tolerances of both methods under varying packing densities. For evaluation, diffuse reflectance NIR and two different Raman measurements with laser illumination diameters of 1 and 6 mm (referred to as the WAI-1 and WAI-6 schemes, respectively) were used to analyze paracetamol tablets with packing densities of 1.1, 1.17, 1.24, and 1.29 g/cm³. ResultsIn all three measurements, increased packing density resulted in an increase in band intensity and an upward-moving baseline due to the variation in void volume (equivalent to porosity) in the tablets. The Raman spectra acquired using the WAI-6 scheme were less sensitive to packing density variations by averaging out different photon propagations over a large area during spectral acquisition. The accuracies for determining paracetamol concentration using the WAI-6 scheme did not significantly deteriorate when the packing density difference was not large, such as between 1.17 and 1.24 g/cm³ (absolute difference of 0.07 g/cm³). The WAI-6 scheme enabled more robust compositional analysis of the tablets with different packing densities. SignificanceThe WAI-6 Raman scheme provides a more robust compositional analysis of tablets under variations in packing density, making it a preferable choice for practical applications. Using the WAI-6 scheme, an additional effective strategy to minimize accuracy deterioration is further beneficial.

Impact of Additives and Packing Density on Fermentation Weight Loss, Microbial Diversity, and Fermentation Quality of Rape Straw Silage

To investigate the effects of the combined addition of Lactiplantibacillus plantarum and sucrose on the fermentation weight loss (FWL), fermentation quality, and microbial community structure of ensiled rape straw under varying packing density conditions. After harvesting, the rapeseed straw was collected, cut into 1–2 cm pieces, and sprayed with sterile water to adjust the moisture content to 60%. The straw was then divided into two groups: one treated with additives (1 × 105 CFU/g fresh material of Lactiplantibacillus plantarum and 10 kg/t fresh material of sucrose), and the other sprayed with an equivalent amount of sterile water as the control (CK). The treated materials were thoroughly mixed and packed into silos at densities of 450, 500, and 550 kg/m3. FWL was recorded on days 1, 3, 6, 15, 20, and 45 of fermentation. On day 45, the samples were analyzed for fermentation quality, microbial counts, and microbial diversity. FWL increased significantly (p < 0.05) in both the treated (LS) and control groups during fermentation. The LS group showed higher lactic acid (LA) levels (p < 0.05) and lower ammonia nitrogen levels (p < 0.05) compared to CK. The CK group had significantly higher (p < 0.05) counts of Coliforms and lower bacterial counts (p < 0.05) than LS. The dominant genera in the silage were Xanthomonas, Lactiplantibacillus plantarum, and Lentilactobacillus. In the LS group, the relative abundances of Lactiplantibacillus plantarum and Lentilactobacillus ranged from 16.93% to 20.43% and 15.63% to 27.46%, respectively, with their combined abundance being higher than in CK. At a packing density of 500 kg/m3, the relative abundances of Lactiplantibacillus plantarum and Lentilactobacillus in the LS group were significantly higher (p < 0.05) than in CK. Increasing packing density and applying additives to rape straw silage effectively reduced FWL, improved fermentation quality, boosted the relative abundance of beneficial lactic acid bacteria, and decreased the presence of undesirable bacteria such as Enterobacter and Bacillus.

Scalable Self-Assembly of Composite Nanofibers into High-Energy-Density Li-Ion Battery Electrodes.

The application of nanosized active particles in Li-ion batteries has been the subject of intense investigation, yielding mixed results in terms of overall benefits. While nanoparticles have shown promise in improving rate performance and reducing issues related to cracking, they have also faced criticism due to side reactions, low packing density, and consequent subpar volumetric battery performance. Interesting processes such as self-assembly have been proposed to increase packing density, but these tend to be incompatible with scalable processes such as roll-to-roll coating, which are essential to manufacture electrodes at scale. Addressing these challenges, this research demonstrates the long-range self-assembly of carbon-decorated V2O5 nanofiber cathodes as a model system. These nanorods are closely packed into thick electrode films, exhibiting a high volumetric capacity of 205 mA h cm-3at 0.2 C. This surpasses the volumetric capacity of unaligned V2O5 nanofiber electrodes (82 mA h cm-3) under the same cycling conditions. We also demonstrate that these energy-dense electrodes retain an excellent capacity of up to 190.4 mA h cm-3(<2% loss) over 500 cycles without needing binders. Finally, we demonstrate that the proposed self-assembly process is compatible with roll-to-roll coating. This work contributes to the development of energy-dense coatings for next-generation battery electrodes with high volumetric energy density.

Effect of blade geometry on the powder spreading process in additive manufacturing

In powder-bed-based additive manufacturing, the quality of the powder bed is closely related to the geometry of the blade used during the powder spreading process. In this study, the spreading process with the vertical blade, inclined blade, and round blade with different radii was performed by discrete element method to investigate the effects of blade geometry on powder spreading. The results show that at the same spreading parameters, the round blade caused the highest density than inclined blade and vertical blade. Increasing the round blade radius can improve the packing density of the powder bed, but it has little effect on the uniformity. The increase in packing density is related to the transitional smoothness of the blade surface at the entrance of the powder bed. The smoother the shape transition of the blade surface at the powder bed entrance, the powders enter the powder bed more gently, so more powders enter the powder bed, resulting in higher packing density. The results may provide suggestions for improving the laser melting process.

Ru Passivation Layer Enables Cu-Cu Direct Bonding at Low Temperatures with Oxidation Inhibition.

Stacking semiconductor chips allows for increased packing density within a given footprint and efficient communication between different functional layers of the chip, leading to higher performance, improved speed, and reduced power consumption. In such vertical stacking, achieving homogeneous electrical and mechanical bonding between heterogeneous chips is crucial, which is termed Cu to Cu direct bonding (CCDB) technology. However, conventional CCDB required a high temperature of over 250 °C to allow Cu diffusion and a vacuum condition for inhibiting Cu oxidation, limiting its practical utilization. Here, we propose that the covering of the Ru layer enables a reliable CCDB as low as 200 °C without concerns regarding oxidation. The bonding strength was as high as 2.24 MPa, and it was endurable at the -45 and 125 °C temperature cycle test for 500 cycles. Through microscopic analysis, we have identified that Cu diffuses through the intercluster boundaries of the Ru layer and moves to the surface, and these atomic Cu ions are recrystallized at the bonding interface, enabling stable bonding at lower temperatures. Specifically, we observed a trade-off between Cu diffusion distance and oxidation inhibition capability depending on the thickness of Ru and found that a 6 nm-thick Ru is optimal, balancing these factors.

Development of geopolymer cold-bonded artificial aggregate for UHPC applications based on fresh packing density

Geopolymer cold-bonded aggregate (GCBA) is a new eco-friendly artificial aggregate manufactured by powder agglomeration. So far the scientific understanding of the powder particle packing within GCBA remains insufficient, which is theoretically crucial for enhancing its mechanical properties. In this study, a high-strength GCBA as the coarse aggregate for ultra-high performance concrete (UHPC) applications was developed using a high dosage of waste brick powder, and a new concept on fresh packing density was innovatively proposed to reflect the actual packing state of the precursor powders within GCBA. The effects of fresh packing density on GCBA's physico-mechanical properties and microstructure were investigated. Results show that the GCBA with the highest fresh packing density had the highest bulk crushing strength over 40 MPa at a reaction degree of only 8.1 %, and the resulting UHPC with this GCBA exhibited an impressive unconfined compressive strength of 162.9 MPa. The increase in fresh packing density led to a significant increase in the hardened GCBA's strength and density, despite it causing a reduction in the GCBA's reaction degree. The microstructural densification of GCBA with higher fresh packing density was formed by closed-packing unreacted precursor powder particles and fewer cyclic-shaped gels, resulting in a significant reduction in the required dosage of activator solution and consequently a decrease in GCBA's cost. A guideline of mixture design for GCBA was finally proposed, which differed from traditional methods by optimizing fresh pellets' performance rather than hardened pellets' performance, promising to be a more economical and efficient avenue for improving GCBA performance.

High-mobility InSnZnO Thin Film Transistors via Introducing Water Vapor Sputtering Gas.

There is always a doubt that introducing water during oxide growing has a positive or negative effect on the properties of oxide films and devices. Herein, a comparison experiment on the condition of keeping the same oxygen atom flux in the sputtering chamber is designed to examine the influences of H2O on In-Sn-Zn-O (ITZO) films and their transistors. In comparison to no-water films, numerous unstable hydrogen-related defects are induced on with-water films at the as-deposited state. Paradoxically, this induction triggers an ordered enhancement in the microstructure of the films during conventional annealing, characterized by a reduction in H-related and vacancy (Vo) defects as well as an increase in film packing density and the M-O network ordering. Ultimately, the no-water thin-film transistors (TFTs) exhibit nonswitching behavior, whereas 5 sccm-water TFT demonstrates excellent electrical performance with a remarkable saturation field-effect mobility (μFE) of 122.10 ± 5.00 cm2·V-1·s-1, a low threshold (Vth) of -2.30 ± 0.40 V, a steep sub-threshold swing (SS) of 0.18 V·dec-1, a high output current (Ion) of 1420 μA, and a small threshold voltage shift ΔVth of -0.77 V in the negative bias stability test (3600 s).

Submicron PAN and nanofiber CTA air filters: Fabrication, optimization, and performance

This study investigates the fabrication, optimization, and performance of submicron polyacrylonitrile (PAN) and nanofiber cellulose triacetate (CTA) air filters produced through electrospinning. PAN fibers with diameters ranging from 379 to 804 nm were generated from PAN/DMF solutions, while genuine CTA nanofibers (65–102 nm) were successfully produced using a recycled CTA polymer and a binary solvent system (DMSO/TCM). The effects of electrospinning parameters, including solution concentration (10–12 wt% for PAN, 8 wt% for CTA), applied voltage (10–16 kV), tip-to-collector distance (16–24 cm), solution supply rate (0.08–0.10 mL/hr), and binary solvent ratio (7:1 to 20:1 DMSO/TCM), on fiber morphology and diameter were systematically examined. Reducing PAN solution concentration and increasing applied voltage effectively decreased fiber diameter, enhancing filtration efficiency. Filtration performance tests revealed that CTA nanofibers outperformed PAN submicron fibers, exhibiting higher quality factors (0.043–0.046 Pa−1) due to their smaller fiber diameters and increased fiber packing density. Decreasing CTA solution supply rate and increasing DMSO/TCM ratio reduced fiber diameter and increased packing density. Longer spinning collection times improved filtration efficiency but increased thickness and pressure drop. The optimization of electrospinning parameters proved crucial for controlling fiber diameter and achieving enhanced filtration efficiency, particularly at the most penetrating particle size (MPPS), which usually covers the ultrafine particle size range. This study provides valuable insights into the development of high-performance air filtration media through the optimization of electrospinning parameters and the utilization of recycled materials.

Numerical analysis of rotating scans’ effect on surface roughness in laser-powder bed fusion

The rotating scanning strategy is a critical factor for top surface roughness in laser-powder bed fusion (L-PBF), yet the underlying mechanism remains elusive. This study introduces an integrated L-PBF model, encompassing powder packing and molten pool fluid dynamics analysis, to investigate how surface roughness accumulates across layers with non-rotating scans but is mitigated with rotating scans. To address computational complexity and prediction errors associated with multi-layer simulations, the model utilizes an experimentally built part as substrate and simulates single-layer depositions with varying scanning rotation angles. Additionally, an as-machined surface representing ideal flat substrate is included for comparative analysis. Results indicate that on as-built surfaces featuring alternating peak-valley patterns, both powder packing structure and fusion zone shape are location-dependent. To effectively characterize the packing structure on such non-flat surfaces, an effective packing density is proposed. Specifically, peak locations exhibit a thinner powder layer, a 14.5% increase in effective packing density, and a 7% decrease in penetration depth compared to valley locations. The circulation flow, driven by recoil pressure and Marangoni force, is responsible for the reduced surface roughness with rotating scans. Specifically, the circulation flow intersects with multiple peaks and valleys, effectively promoting material redistribution among these tracks and disrupting the peak-valley patterns. Conversely, the peak-valley patterns are preserved and may propagate to subsequent layers with non-rotating scans.

Capacitive BaTiO3-PDMS hand-gesture sensor: Insights into sensing mechanisms and signal classification with machine learning

Flexible sensors have gained extensive interest because of their versatile applications in healthcare, robotics, and wearable devices. This study introduces a capacitive sensor utilizing barium titanate oxide (BaTiO3)-polydimethylsiloxane (PDMS) for bending sensing and addresses crucial performance parameters including sensitivity, repeatability, response time, and durability. The sensor exhibited a notable capacitance change of 42.85% in conjunction with fast (1 s) responses and recovery times, and minimal hysteresis (<2%). Its reliable performance across varying bending rates and durability through extensive cyclic tests underscore its applicability in real-world scenarios. Importantly, the sensor's capabilities were enhanced by integrating machine learning (ML), achieving an impressive accuracy of 97.11% in recognizing hand-sign language gestures. Furthermore, finite element analysis was employed to validate the correlation between the increase in compression-induced packing density and capacitance enhancement. This holistic integration of advanced materials, computational simulations, and ML not only extends the boundaries of sensor technology but also holds promise for revolutionizing human–machine interactions, aiding speech-impaired individuals, and enriching virtual reality experiences. This study represents a pivotal advancement in the field of flexible sensors and the unlocking of new dimensions of their applications.

Effect of cylinder wall parameters on the final packing density of mono-disperse spheres subject to three-dimensional vibrations

Achieving densely packed particles is desirable within the industries of ceramics, pharmaceuticals, defence and additive manufacturing. In this work, we use the discrete element method (DEM) to determine the effect of wall parameters on the final packing density of mono-disperse spheres subject to 4 varying three-dimensional vibration and fill conditions. We focus specifically on the impact of the container wall parameters on the particles' final packing density. Following on from the validation of the DEM simulation the particle-wall coefficient of restitution, the particle-wall coefficient of rolling friction and the particle-wall coefficient of sliding friction were varied individually and the effect on the final packing density analysed. For relatively low particle-particle friction glass beads, the effect of these wall properties had no discernible effect on the final packing density achieved. Following on from these findings the particle-wall properties were varied at the extreme values of particle-particle coefficient of rolling friction and particle-particle coefficient of sliding friction. For a particle-particle coefficient of sliding friction = 1, increases in particle-wall coefficient of restitution resulted in a minor increase in the final packing density of particles though this was not statistically significant. For a particle-particle coefficient of sliding friction = 1, increases in particle-wall coefficient of rolling friction resulted in a minor decrease in the final packing density of the particles though again not to a degree where the trend can, with complete certainty, be distinguished from the random error across the repeats. Finally, when the particle-particle coefficient of sliding friction = 1, increases in particle-wall coefficient of sliding friction resulted in a significant decrease in the final packing density of particles. This decrease was attributed to the propagation of force chains throughout the packing. The significant decrease in final packing density with particle-wall coefficient of sliding friction highlights the need to choose appropriate vessel materials to optimise packing of particles with a high particle-particle coefficient sliding friction. Conversely, for particles with minimal particle-particle friction, the particle-wall friction coefficient has no effect on the final packing density of particles - a potentially valuable finding for certain industrial applications. All simulations were run using the open-source DEM package LIGGGHTS on the University of Birmingham's high-performance computer: BlueBEAR. All the code files used within this paper can be found on Github: https://github.com/Jack-Grogan/DEM-Vibropacking-Wall-Effects.

Energetic and Entropic Motifs in Vesicle Morphogenesis in Amphiphilic Diblock Copolymer Solutions

Coarse-grained molecular dynamic simulations are employed to investigate the spatiotemporal evolution of vesicles (polymersomes) via self-assembly of randomly distributed amphiphilic diblock copolymers PB-PEO (Poly(Butadiene)-b-Poly(Ethylene Oxide)) in water. The vesiculation pathway consists of several intermediate structures, such as spherical/rodlike aggregates, wormlike micelles, lamellae, and cavities. The lamella-to-vesicle transition occurs at a constant aggregation number and is accompanied by a reduction in the solvent-accessible surface area. Simulation predictions are in qualitative agreement with the mechanism of vesicle formation in which the unfavorable hydrophobic interactions between water molecules and polymer segments, along the edge of the lamella, are eliminated at the expense of gaining curvature energy. However, rod–lamella–vesicle transition is accompanied by an increase in copolymer packing density. Hence, the change in the surface area accompanying vesiculation predicted by the simulations is significantly lower than theoretical estimates. Changes in information entropy, quantified by the expectation of the logarithm of the probability distribution function of the segmental stretch parameter s, defined as the difference between the maximum and instantaneous segmental extension, are statistically insignificant along the vesiculation pathway. For rods, lamellae, and polymersomes, s follows a log normal distribution. This is explained based on the configurational dynamics of a single diblock chain in water.

A review of microfabrication approaches for the development of thin, flattened heat pipes and vapor chambers for passive electronic cooling applications

With the rapid development of microelectronics and the telecommunication industry, a variety of high performance, portable and slim electronic devices have become available. Miniaturization of devices and increased packing density of electronics can generate “hot spots” i.e. a high heat flux on a small area. Thus, in such devices the heat management requirements go beyond the limits of typical approaches and the development of miniaturized, high-performance thermal management concepts to cool high-performance, compact electronic devices is urgently required. To this direction, micro and nanofabrication methods can provide solutions in both miniaturizing existing concepts of passive cooling as well as in improving their performance. In this review, we start by introducing the most commonly used metrics used to evaluate the performance of passive cooling devices (i.e. vapor chambers and flattened heat pipes) together with the most prominent performance limitations. Then, in the main part, we present state of the art examples of microfabricated, thin vapor chambers and flattened heat pipes on rigid substrates (i.e. using metals and silicon), but also vapor chambers on thin and flexible polymeric or composite materials. Finally, the main conclusions and the steps which should be followed to further enhance the performance of such devices are summarized in the conclusions and future perspectives section.

Phonon Thermal Transport at Interfaces of a Graphene/Vertically Aligned Carbon Nanotubes/Hexagonal Boron Nitride Sandwiched Heterostructure

Molecular dynamics simulation is used to calculate the interfacial thermal resistance of a graphene/carbon nanotubes/hexagonal boron nitride (Gr/CNTs/hBN) sandwiched heterostructure, in which vertically aligned carbon nanotube (VACNT) arrays are covalently bonded to graphene and hexagonal boron nitride layers. We find that the interfacial thermal resistance (ITR) of the Gr/VACNT/hBN sandwiched heterostructure is one to two orders of magnitude smaller than the ITR of a Gr/hBN van der Waals heterostructure with the same plane size. It is observed that covalent bonding effectively enhances the phonon coupling between Gr and hBN layers, resulting in an increase in the overlap factor of phonon density of states between Gr and hBN, thus reducing the ITR of Gr and hBN. In addition, the chirality, size (diameter and length), and packing density of sandwich-layer VACNTs have an important influence on the ITR of the heterostructure. Under the same CNT diameter and length, the ITR of the sandwiched heterostructure with armchair-shaped VACNTs is higher than that of the sandwiched heterostructure with zigzag-shaped VACNTs due to the different chemical bonding of chiral CNTs with Gr and hBN. When the armchair-shaped CNT diameter increases or the length decreases, the ITR of the sandwiched heterostructure tends to decrease. Moreover, the increase in the VACNT packing density also leads to a continuous decrease in the ITR of the sandwiched heterostructure, attributed to the extremely high intrinsic thermal conductivity of CNTs and the increase of out-of-plane heat transfer channels. This work may be helpful for understanding the mechanism for ITR in multilayer vertical heterostructures, and provides theoretical guidance for a new strategy to regulate the interlayer thermal resistance of heterostructures by optimizing the design of sandwich layer thermal interface materials.

1D modeling of methanation reactor with circulation (MeRCi) for assessment of reaction characteristics

For a power-to-gas (PtG) system, methanation has attracted attention to synthesize methane from carbon dioxide and hydrogen. There is a problem that heat generated by the reaction causes thermal degradation of the catalyst. Then, we have proposed a methanation reactor with circulation (MeRCi), where the temperature of the catalyst bed is controlled by recycling a part of the product gas. In this study, a one-dimensional model of the MeRCi was developed, and the methanation process was numerically simulated for assessment of reaction characteristics. The catalyst amount, the recycle ratio, and the catalyst bed length were changed. For comparison, the simulation of a straight-tube fixed-bed reactor was also simulated. Based on the gas temperature distribution of the straight-tube reactor, the simulation results show a good agreement with the experimental data, and the validity of our numerical model was confirmed. Even for the higher recycle ratio, the methane conversion rate at the reactor outlet does not change much, showing the high conversion rate within the simulation conditions. The increase of the catalyst packing density as well as the catalyst bed length enlarges the methane conversion rate. By considering the fact that the methane conversion rate is sufficiently high when the catalyst packing density is over 500 kg/m3, the reaction rate must be kept at certain level to keep the high methane conversion rate. As for the catalyst bed length, there is a minimum value at which the methane conversion rate is unexpectedly dropped where unreacted hydrogen and carbon dioxide are retained in the products.

Dynamic low power management technique for decision directed inter-layer communication in three dimensional wireless network on chip

3D ICs, a novel technology, might significantly impact multicore NoCs with hundreds or thousands of processing components on a single chip. Multiple 2D chips can be stacked vertically to create multiple active processing elements at various levels. Adding active device layers to 3D ICs can enhance system performance, increase functionality, and increase packing density. New architectural and IC technology advancements hinder energy-efficient design research. Achieving a balance between chip power and performance is crucial. This paper describes the “Dynamic Low Power Management Method in 3DWiNoC” (DLPM 3DWiNoC) architecture, which enables self-organized, centrally managed service management using Smart Master Agents. The approach utilizes SMA's ODA DD module for self-organized, centrally managed service management. To improve power regulation, data flow across vertical interconnects (TSVs) is reconfigured based on a dynamic evaluation of channel link use. SMA aims to reduce congestion by increasing connection utilization through high-frequency, bi-directional vertical channels via TSVs. The suggested system is modeled in MATLAB Simulink. Compared to 3D stacking, TSV stacking of vertical interconnects with the SMA method ensures low parasitic (latency and power) and higher bandwidth with higher vertical wire densities. Experimental results show that the proposed architecture decreases area overhead by 5%-7%, network latency by 12%-15%, and NoC power consumption by 15%-20% compared to the present multi-NoC design.

Effect of uniaxial stretching on gas separation performance of polyimide membranes

Fine-tuning of the physical stacking structure for microporous polyimide (PI) membranes via the stretching processing is a practical way of achieving advanced membrane materials with improved aging resistance as well as high gas separation performance. Here, a fluorinated polyimide 6FDA:BPDA-TFDB(1:1:2) is used as a prototype and a series of stretched membranes X%-PI are fabricated by uniaxially stretching the membrane to different elongation ratio and then annealing. Based on birefringence and wide-angle X-ray diffraction measurements, it's found that regular orientation of polymer chains along the stretching direction and fine-tuning of d-spaces from interchain packing and π-π stacking happen during the uniaxial stretching process. As such, compared to pristine PI membrane, the stretched membranes show better mechanical and thermal stability, especially for the one with higher stretching ratio. In addition, owing to the increased packing density of polymer chains, the highly stretched membrane of 40%-PI shows significantly improved gas perm-selectivity by 32.8%, 24.3%, and 12.6% for He/CH4, H2/CH4, and CO2/CH4 gas pairs, respectively, in comparison to pristine membrane. Furthermore, 40%-PI exhibits much higher gas permeability retention rate than that of other membranes after three months' aging. We expect that this work can offer polymer materials processing guidance for the preparation of high-performance gas separation membrane in future.

Spatial correlation and pore morphology analysis of limestone calcined clay cement (LC3) via machine learning and image-based characterisation

Comprehending the microstructure of LC3 is of paramount importance since it governs majority properties of cement. Here, we investigate the spatial correlation and pore morphology of LC3, revealing microstructural refinement effects through deep learning and image-based characterisation. A deep learning model was developed to characterise the spatial correlation of the local features of 28-day LC3 with optimised resolution and physical image size, identifying a lower probability of connected pores occurring but a higher likelihood of connected solid particles in LC3 than in OPC. A 33% lower maximum correlation revealed by two-point correlation analysis inferred that LC3 possessed a smaller RVE size and increased packing density. The pore morphological analysis based on BSE images indicated a higher hydration rate and pore deformation in LC3. These findings demonstrate the microstructural refinement mechanisms of LC3 but also lay the foundation for localised microstructural characterisation of cementitious materials with the potential to complement existing traditional analyses.

Modeling crushable soils incorporating density effects via coordination number

A rational constitutive model of crushable soils is proposed based on a novel evolution law for the grading index, which incorporates the effect of packing density on the particle crushing phenomena through the coordination number as an intermediate variable. The evolution law of the grading index reasonably combines the increase in the coordination number due to an increase in packing density; and the increase in the crushing resistance due to the increase in the coordination number. The effect of particle crushing on the stress–strain response is incorporated by lowering the critical state specific volume with the changing grading due to crushing. The validity of the proposed constitutive model was verified with an extensive series of elementary tests and DEM. The proposed model properly predicted two seemingly contradictory experimental evidence for crushable soils that: densely packed soil exhibits lesser crushing than loosely packed one under the same effective stress paths; densely packed soil is more likely to crush than loosely packed one when it is sheared. This approach can predict the stress–strain response of crushable soils under different packing densities and stress paths, offering valuable insights for comprehending the crushing responses.

A Theoretical and Experimental Study of Oil Wicking Mechanism of Kapok Fibrous Powder Assembly

ABSTRACT Kapok fiber has a large lumen with a natural waxy surface which endows it with distinct hydrophobic-oleophilic properties. Oil-impregnated kapok fibrous powder (KFP) has great potential as a lubricant carrier material. To study the oil wicking mechanism of KFP assemblies with different pore structures (interfibrous pores and the lumens), a dual-scale model was established based on Washburn capillary theory. The theoretical model was verified by capillary rise test of KFP assemblies in various packing densities ranging from 0.08 g/cm3 to 0.14 g/cm3. It was found that the experimental results have good consistency with theoretical values at low packing densities. The deviation between the experimental result and the theoretical value increases with the increase of packing density. This can be largely attributed to compression of the lumens at increased packing density, leading to the reduction of oil sorption capacity within the lumens. The outcomes of this research are believed to provide important references for the usage of fibrous powder materials as lubricant carrier.