Particle Grain Research Articles

Sedimentation of cohesive sediments at the subtidal flat affected by wind wave in high turbidity estuary

Sedimentation is an important mechanism to mitigate the shrinking of tidal flat and to restore its ecological function by means of sand or mud nourishment. To explore the sedimentation of cohesive sediments, a seabed tripod observation system was deployed at the subtidal region of the Hengsha Shoal adjacent to the turbidity maximum zone of the Yangtze Estuary for 11 days. The results showed that the fine sediment with the median grain size around 8 mm occupied the whole water column. The seabed was in relative equilibrium state with the fluctuation of bed level smaller than 16 mm during the moderate wind condition while the seabed experienced a rapid erosion of 38mm and a successive intensive accretion of 68mm during the process of wind wave and swell. The bottom hydrodynamic at 0.3mab during the bed accretion was stronger than that during the bed erosion. The deposition process of cohesive sediments can be better described by the simultaneous deposition paradigm than that by the exclusive deposition paradigm according to the direct data-model comparison of the bed level changes, especially during the impact of fluid mud. Three possible reasons for the better performance of the simultaneous deposition paradigm were proposed. The first possibility is that the fine suspended sediments do maintain a continuous contact with the sediment bed since the direct bed level changes during our observation period has been well reproduced by the simultaneous deposition paradigm. The second possibility is the SSC-induced turbulence damping which facilitates the fine sediment settling in the form of cohesive sediment flocs, indicating the settling of sediments can’t be judged by the critical shear stress for deposition just based on the single particle grain size. The last possibility is the fluid mud-induced overestimated bed shear stress by using turbulent velocity fluctuation above the fluid mud-water interface, which produces excess sediment erosion waiting to be compensated by the simultaneous deposition paradigm. For practical modeling purposes, modeling under the simultaneous deposition paradigm can give satisfactory results for the sedimentation of cohesive sediment especially during the impact of wave or swell.

Study of Ra desorption processes in an estuary system with high-turbidity at the Southeast China

Radium (Ra) isotopes are extensively used as geochemical tracers for studying water mass mixing and submarine groundwater discharge in marginal and coastal seas. However, river-borne particles and seafloor sediments are an important source of Ra in marine systems due to Ra desorption. Therefore, it is necessary to study the desorption behaviors of Ra isotopes in river sediment or suspended particles. Here, the desorption behaviors of four Ra isotopes (223Ra, 224Ra, 226Ra, and 228Ra) in the Zhangjiang River sediments were investigated by a series of designed variable-controlling experiments in the laboratory. Within the designed salinity range, desorption amounts of Ra isotopes increased with increasing salinity, and when the salinity was greater than 15 ppt, Ra desorption reached an equilibrium state. Overall, desorption of Ra isotopes increased with the decrease of particle grain size, however, the desorption fractions of 224Ra and 228Ra decreased with decreasing particle size due to the increase of original Ra activities in smaller sediment particles. In the experiments, we found that two sediment samples with similar mean grain size (3.8 μm and 3.3 μm) and similar grain size distributions had significantly different Ra desorption under the same conditions. The results of mineral composition analysis based on X-ray diffraction showed that these two samples had different percentages of kaolinite, quartz, and plagioclase, which indicated that the mineral composition of particles had an important effect on Ra isotope desorption. In conclusion, salinity, particle grain size, and mineral composition all had significant effects on Ra desorption behaviors of sediment particles. Based on the above desorption experiments, the desorbed fluxes of four Ra isotopes from river-borne sediments to the Dongshan Bay were estimated to be (5.95 ± 1.47) × 107 Bq yr−1 for 223Ra, (1.95 ± 0.27) × 109 Bq yr−1 for 224Ra, (2.73 ± 0.47) × 108 Bq yr−1 for 226Ra, and (1.26 ± 0.20) × 109 Bq yr−1 for 228Ra, respectively.

Experimental investigation on the effet of input paramètres on surface roughness and MRR of abrasive flow machining process

A crucial and costly step in the whole manufacturing process is the precision and super finishing procedure. A step of final finishing is involved in the production of precision components. It accounts for a respectable portion of the cost of production overall, is mostly uncontrolled, and requires a lot of manpower. Abrasive finish methods are being developed to address issues including high direct costs and the production of precision components with particular characteristics for finishing inaccessible places. A vast number of cutting blades with arbitrary orientation and shape are used in the abrasive finishing process. Due to their ability to complete a variety of form geometries with the appropriate dimensional accuracy and surface polish, abrasive fine procedures are often used. The unconventional finishing method known as AFM (abrasive flow machining) presses abrasive viscoelastic polymer on the surface of work piece. Al7075/SiC NMMCs’ internal rounded and hollow surfaces are completed using an AFM trial procedure that is constructed and designed in conjunction with specially produced medium. Workpieces are created using a lathe shortly after stir casting metal matrix nano composites with cross sections of 25 mm in diameter and containing 1 percent,1 ,2,3,4 nano-Sic (50 nm) by weight. Extrusion pressure abrasive particle grain size number of cycles were evaluated for their surface roughness (Ra) than material removal (MR), respectively. The evaluation of the material’s qualities, such as density, hardness, and tensile strength The improvement in the surface completeness of these NMMCs is further shown by the scanning Microscopy OM, EDS SEM, and XED analyses.

A Review of Research on Galvanic Corrosion of Aluminum Alloys

When aluminum alloys are coupled with dissimilar materials, they often act as corrosion anodes and are suscepted to accelerated corrosion. Therefore, deepening our knowledge of such corrosion phenomena, related mechanisms, and elaborating new prediction model is of great theoretical and practical significance. In this paper, such mechanisms are explained from both macroscopic and microscopic points of view by considering several aspects such as the second phase particle type, grain size, and environmental ions. More specifically, different perspectives on such a problem are elaborated, which take into account: the properties of the coupling pair materials, geometrical characteristics, environmental media characteristics, the corrosion regularity of different types of aluminum alloys, the influence of area ratio on anode corrosion current density, the interference of the solution primary ions represented by Cl- and the accompanying ions represented by Al3+. A review is also conducted of the standard test methods used in the study of aluminum alloys galvanic corrosion and of research methods such as the Wire Beam Electrodes Technology (WBE), the Scanning Kelvin Probe Force Microscopy (SKPFM) technology. Finally, three kinds of inhibition technologies are discussed, including the anodic oxidation treatment, the corrosion inhibitor treatment and the coating protection method.

Effects of reinforcement grain size and concentration on the physicomechanical properties of green automotive brakepads from waste cowhorns and rockshells

This study presents the development and characterization of green automotive brakepads using cowhorn (CH) and Rockshell (Thias Coronata L.) (R) as reinforcement material in full factorial experiments. The brakepads were produced by compression moulding at 220.73N using epoxy resin binder, CaCO3 fillers, Diethylenetriamine hardener, colourless methyl-ethyl ketone peroxide (MEKP) catalyst, carbon black friction modifier, with copper and iron fillings as thermal conductivity additives. Three levels of particle grain sizes 125, 250, 500µm were produced from each material. Hybrid CHR samples were also produced with same grain sizes. The density, hardness, and compressive strength properties were observed to reduce with increase in grain size while liquid absorption increased with increase in grain size. Impregnating the reinforcement materials with increasing concentration of R-particles improved the hardness, compressive strength and liquid absorption but decreased the friction coefficient. The R-samples performed best among all in liquid absorption, except for oil absorption where the commercial (control) sample surpassed it. EDX spectroscopy results showed presence of antimony and vanadium toxic heavy metals in the control sample unlike the developed brakepads. All properties measured exhibited multivariate quadratic regression models with good fitness of R2-values, 0.8438 ≤ R2 ≤ 0.9976, and significance-F values, 0.000398 ≤ significance F. ≤ 0.18101. All response surfaces showed best performance with R-concentration of 80 – 100% and 125 – 250µm grain size ranges. Hence, reinforcements of cowhorn and rockshell particles with concentration and grain sizes above can be used to develop brakepads with properties superior to the toxic control brakepads.

Some optical and microstructure characteristics of effective cost ZnO-containing hydroxyapatite

Metal oxide like zinc oxide (ZnO) is recognized to be one of the versatile inorganic compounds due to its physical properties. Crystalline compositions, morphology, particle size, and chemical bonds of pure hydroxyapatite (HA) and ZnO/HA were characterized by x-ray diffraction (XRD), Scanning and transmission electron microscopy (SEM and TEM), Fourier transform infrared spectroscopy (FT-IR), and Raman scattering detected crystalline and bond structure. Nanocomposites were crystallized in a main monoclinic phase of HA and a minor hexagonal phase of ZnO with particle size (18–29 nm) and grain size (75–200 nm) for the synthesized samples were identified. Moreover, the existence of the phosphate, carbonate ions, and hydroxyl groups in the HA and its composites structure was assured by the FT-IR assessment. The optical bandgap (Eg) of HA showed two transitions at 3.24 and 4.37 eV; these values decreased with the incorporation of ZnO. The determining optical and photoluminescence properties confirmed the presence of ZnO content in the HA matrix.

A first wind tunnel study on the aeolian sand transport of coral sands

Although wind-blown sand activity may be crucial for the landform and stability of coral islands in the ocean, the characteristics of coral sand movement remain largely unknown. This study is the first to quantify coral sand flux by wind tunnel measurement with various wind speeds using coral samples collected from an island and a sand cay from Yongle Atoll, Xisha Island in the South China Sea. The particle morphology, grain size, chemical and mineral composition, as well as threshold wind speed, transport rate, and transport flux profile of blowing coral sands, were investigated and compared to those of quartz sands from an inland desert. The basic features of coral sand movement, including an increase in threshold wind speed with grain size and density, an increase in total rate with wind speed, and an exponential decrease in transported sand concentration with height, have been determined. Cay sands with a grain size of about 1.24 mm behave similarly to coarse quartz sands, whereas island sands with a grain size of 0.49 mm perform similarly to medium and medium coarse quartz sands. Contrary to normal desert and beach sands, the decay trend of the flux profile of coarse coral sand increases with wind speed, just as it does for coarse desert sand. Due to their irregular morphology, coral sands are difficult to entrain by wind, with a threshold wind speed of about 11.64 m s−1 for island sand and 16.98 m s−1 for cay sand, which are much greater than the 4.32 m s−1 for fine and 12.67 m s−1 for coarse desert sands in the wind tunnel. The results can be incorporated into existing sand transportation models and used to evaluate the influence of aeolian processes on the landform of coral islands.

Effects of cow dung ash and calcium hydroxide on geotechnical properties of expansive and loose soil

The study is an investigation into the effects of CDA and Ca (OH)2 on geotechnical properties of expansive (Sample A) and loose soil (Sample B). The experiments were designed to study the effects of adding CDA in various percentages by weight (5%, 15% and 15%) of dry soil with 5% constant Ca (OH)2, which produces pozzolanic reactions in soil samples. Sample A was collected at Moniya, Ibadan, Sample B from The polytechnic, Ibadan and, cow dung was obtained from a farm settlement at Ilora, Oyo State, the dung was air dried and then calcined at 500 0C – 600 0C, after which it was sieved using 600µm sieve. The samples were subjected to the following laboratory tests; Natural moisture content, Particle (grain) size analysis, Atterberg limit test, Compaction test, California bearing ratio (CBR) test. The NMC test shows that sample A retains more water than sample B given by the values 26% and 6% respectively, the particle size analysis results showed that sample A has highest percentage of clay passing sieve no. 200 (75µm) i.e. 62.86%, while sample B has 7.27%, this indicates that sample A with high silt clay content are susceptible to volume changes when wet. The liquid limit and plasticity index for sample A is 49% and 28% respectively while sample B is a cohesionless soil. This shows that sample A has high clay content and its load bearing capacity could be reduced when wet. The AASHTO system classified sample A as A-7-6, and sample B as A-3. This shows sample A is fair to poor while sample B is excellent to good. The maximum dry densities ranged from 1.61mg/m3 to 1.87mg/m3 and Optimum moisture contents range from 19.2% to 16.36% respectively. The CBR value of sample A as to the varying percentage are 2.07%, 10.62% (0% CDA & 5% Ca(OH)2) , 12.69%, 16.77%, 31.41% while CBR value of sample B are thus: 32.7%, 27.06% (0% CDA & 5% Ca(OH)2), 12.09%, 16.2%, 16.74%. It was then observed that CDA at 15% and Ca(OH)2 at 5% is the optimum for expansive soils while adding CDA and Ca(OH)2 to loose soil will increase the OMC and thus reduce its engineering properties.

MECHANICAL AND TRIBOLOGICAL CHARACTERIZATION OF HYBRID Al6061/B4C/Gr COMPOSITES BY STIR CASTING TECHNIQUE

This research focuses on the fabrication of Al6061/B4C/Gr metal matrix composites as well as the mechanical and wear properties analysis. A liquid metallurgy stir casting process was used to cast the Al6061 alloy matrix composites with specific wt.% of B4C and constant wt.% of graphite. In this work, newly developed composites of Gr (particle grain size: 0–20[Formula: see text][Formula: see text]m) and B4C (particle grain size: 0–30[Formula: see text][Formula: see text]m) are reinforced with Al6061 pure alloy, which enhanced the mechanical and wear properties when compared to Al6061 pure alloy. Microstructure analysis was carried out concerning the developed mechanical properties. Furthermore, the dry sliding wear behavior of Al6061/B4C/Gr metal matrix composites was investigated at a sliding speed of 1[Formula: see text]m/s and a sliding distance of 1500[Formula: see text]mm against a hardened EN-31 disc under the corresponding load of 19.68[Formula: see text]N. The minimum wear rate is [Formula: see text][Formula: see text]mm3/m found at 15[Formula: see text]wt.% B4C and 2[Formula: see text]wt.% graphite and the coefficient of friction is 0.54 that decreases with graphite addition, with the lowest value obtained with 5[Formula: see text]wt.% B4C and 2[Formula: see text]wt.% graphite. Al6061/10[Formula: see text]wt.% B4C/2[Formula: see text]wt.% Gr particles-reinforced composite material demonstrated the highest tensile and flexural strengths. The hardness,compressive and tensile strength of the Al6061/15[Formula: see text]wt.% B4C/2[Formula: see text]wt.% Gr particles-reinforced composite material were the highest. Scanning electron microscopy was used to examine the worn surfaces of wear specimens. The main objective of this work is to develop hybrid Al6061/B4C/Gr composites with improved mechanical and wear properties when compared with the base alloy. Al6061 is widely used in automobiles parts like engine block, piston rings, alloy wheels, marine industries, etc. B4C used in the composite improves strength and is used commonly in armed bullet proof. The Gr present in the composite improves wear resistance, and therefore applied in wear-resistant parts like brake, piston with cylinder, etc.

A parametric study of the microstructural evolution of an advanced Ni-based superalloy powder when consolidated using Field Assisted Sintering Technology, compared to a hot isostatic pressing benchmark

The use of Field Assisted Sintering Technology (FAST) is examined for the consolidation of an advanced Ni-based superalloy powder feedstock. FAST processed material was directly compared to a benchmark material prepared via hot isostatic pressing (HIP) where it was found that density, hardness values and microstructures were comparable. FAST enables the retainment of the prior particle grain morphology when using sintering dwell times ranging from 10 to 240 min. The application of dwell temperatures above the γ′ solvus of the alloy resulted in significant grain growth. Measured densities reveal that the applied load and dwell time used during sintering have minimal effect on the final density of the consolidated material. The crystallographic texture was also shown to be isotropic in FAST consolidated material. This study demonstrates that FAST is potentially a viable complementary and/or alternative processing route for consolidating Ni-based superalloy powders.

Grain Refiner Settling and Its Effect on the Melt Quality of Aluminum Casting Alloys.

Grain refiner particles, which are intended to induce the formation of fine equiaxed grain structure during the solidification of aluminum alloys, are prone to settling during the holding of the liquid metal, which phenomenon can affect not only the grain size but the spatial distribution of the double oxide films in the melt. In this study, the settling of Al3Ti inoculant particles, as well as its effects on melt quality and grain refinement, were studied. During the experiments, the Ti-concentration of a liquid Al-Si-Mg-Cu alloy was increased to 0.3 wt.% by the addition of Al-10%Ti master alloy at different melt temperatures. Particle settling and grain size evolution were studied by quantitative metallography, while the interactions of grain refiners and bifilms were investigated by scanning electron microscopy (SEM). The evolution of melt quality was assessed by the computed tomographic (CT) analysis of reduced pressure test (RPT) samples. It was found that effective grain refinement was only realized when the introduced blocky Al3Ti particles were dissolved and re-precipitated in the form of (Al,Si)3Ti at a lower temperature. Without dissolving at higher holding temperatures, Al3Ti particle settling has taken place within 10 min. The settling of (Al,Si)3Ti particles improved melt quality by the aided sedimentation of bifilms in the melt.

An Alternative Technology to Obtain Dewatered Mine Tailings: Safe and Control Environmental Management of Filtered and Thickened Copper Mine Tailings in Chile

An alternative process to obtain a high degree of dewatering tailings that produces a high-density product is presented in this article. This technology involves the combination of tailings particle grain size classification by hydrocyclones (HC) and tailings dewatering by horizontal vibratory screens (HVS). It makes it possible to dewater tailings to a high grade of performance. This alternative technology (HC-HVS) involves the recovery of water from the coarse fraction of tailings (sands) through two hydrocycloning stages, followed by a dewatering stage of cycloned tailings sands on horizontal vibratory screens, to reduce moisture content and turn it into a “cake”. The resulting coarse fraction tailings are easily transported to a dry stack tailings storage facility (TSF). The fine fraction of tailings (slimes) can be dewatered on thickener equipment to recover part of the process water. Finally, this article describes the main benefits of this alternative dewatered tailings technology with an emphasis on (i) dewatering technology evolution over the last 17 years; (ii) process stages features; (iii) pilot test results; (iv) tailings properties analysis (such as particle grain size distribution, fines content) and (v) lessons learned about the experience gained in the operation of Mantos Blancos case study with dry stack tailings storage facility.

Geometry optimisation of an industrial thermocline Thermal Energy Storage combining exergy, Life Cycle Assessment and Life Cycle Cost Analysis

Recently, packed-bed storage has been considered as a promising alternative solution for thermal energy storage especially for waste heat recovery in industrial plants. This work aims to optimise environmental footprint, costs and exergy efficiency of a thermocline thermal energy storage through two optimisation variables. These variables describe the tank shape and the particle grain size. Two solid filler materials are compared: machined ceramic and ceramic from fly ashes. The reference storage is an existing industrial high-temperature air/bauxite packed-bed storage called Eco-Stock®. A one-dimensional two-phase (fluid and solid) model is used to determine the energy and exergy performance of the thermocline tank. For the life cycle assessment, four indicators are selected: cumulative energy demand, global warming potential, abiotic depletion potential and particulate matter. Finally, a life cycle cost analysis is performed to determine levelised cost of energy used as economic criterion. This multi-objective problem is solved by the multi-criteria genetic algorithm available on the Matlab® platform. A Pareto set is obtained, bounded by the single exergy and environmental optimisation solutions. The economic optimisation is found on the Pareto set, close to the environmental optimal solution. Favouring economic performance reduces the environmental footprint of the storage. Despite better exergy performance and smaller tank volume, the exergy-optimised tank increases environmental impacts and costs due to higher pumping work. The environmental and economic optimisations lead to stocky tank shapes while a tapered tank is obtained for the exergy optimisation. According to the TOPSIS method, the economic optimal solution appears to be the best trade-off for both fillers tested. Despite poorer thermophysical properties, the solution with ceramic from fly ashes shows similar exergy and economic performance as the machined ceramic solution (more than 96 % of exergy efficiency for 3.1 c€/kWhth), while the environmental footprint is greatly reduced (61 vs 87 ca.year). This tank has a diameter of 2.6 m and a height of 1.7 m. The particle diameter is 11 mm.

Improving hydrogen storage thermodynamics and kinetics of Ce-Mg-Ni-based alloy by mechanical milling with TiF3

Mg-based hydrides are too stable and the kinetics of hydrogen absorption and desorption is not satisfactory. An efficient way to improve these shortcomings is to employ reactive ball milling to synthesize the nanocomposite materials of Mg and additives. In this experiment, TiF3 was selected as an additive, and the mechanical milling method was employed to prepare the experimental alloys. The alloys used in this experiment were the as-cast Ce5Mg85Ni10, as-milled Ce5Mg85Ni10 and Ce5Mg85Ni10 + 3 wt.% TiF3. The phase transformation, structural evolution, isothermal and non-isothermal hydrogenation and dehydrogenation performances of the alloys were inspected by XRD, SEM, TEM, Sievert apparatus, DSC and TGA. It revealed that nanocrystalline appeared in the as-milled samples. Compared with the as-cast alloy, ball milling made the particle dimension and grain size decrease dramatically and the defect density increase significantly. The addition of TiF3 made the surface of ball milling alloy particles markedly coarser and more irregular. Ball milling and adding TiF3 distinctly improved the activation and kinetics of the alloys. Moreover, ball milling along with TiF3 can decrease the onset dehydrogenation temperature of Mg-based hydrides and slightly ameliorate their thermodynamics.

Linking Thermal Runaway and Cycling Degradation of Lithium-Ion Batteries Using Multi-Scale X-Ray Imaging

To meet the increasing energy demands of portable devices and electric vehicles, high-nickel lithium-ion cathode materials with the general formula Li(NixMnyCoz)O2 (NMCXYZ) have been extensively researched. Currently, NMC811 is used commercially due to its high capacity and low cobalt content. However, capacity fade is still a prominent issue, with a variety of degradation mechanisms responsible. Of particular interest is secondary particle cracking, where the stress-strain effect of c-parameter expansion in the NMC crystal lattice leads to fractures. Boundaries between the primary particle grain that make up the secondary particle structure act as nucleation points for particle cracking. The exposed surface then reacts with the liquid electrolyte, leading to oxygen evolution and capacity loss. Single-crystal materials have shown promise as a method of improving cycle life, as the lack of agglomerated primary grains appear to make the monocrystalline particles more resilient to the mechanical strain of expansion during charging1.In parallel with the cycle life concerns, attention over battery safety continues to increase as instances of catastrophic battery failure are publicised across the world. While the specific steps that lead to battery thermal runaway have been extensively researched, the safety and thermal stability of degraded cells remains a scarcely investigated topic2. To that end, the goal of this work is to characterise the safety properties of different NMC morphologies, and study how charge-discharge cycling affects the thermal stability of these materials.In this work, we have combined accelerating rate calorimetry (ARC) with lab-based, post-mortem macro, micro and nano X-ray CT to observe the influence of cell structure on thermal runaway of NMC811 pouch cells with single-crystal and polycrystalline cathode materials in both the pristine and aged state. The results presented show that when pristine, the larger surface area of single-crystal materials provides more reaction sites and leads to a lower self-heating onset and thermal runaway initiation temperature compared to polycrystalline, suggesting a lower thermal stability. However, as polycrystalline particles break up during thermal runaway, the fragments create fresh surface to react with the electrolyte and continue the series of exothermic reactions, leading to a higher peak temperature. Macro-CT has revealed how the wound jellyroll structure of the cell focuses the force of the explosion through the flat sides of the cells, possibly increasing the likelihood of failure propagation. It has also been observed that the polycrystalline materials show a greater material ejection out from the centre of the cell, reinforcing the findings from the ARC investigations that although polycrystalline cells are more thermally stable initially, the peak temperatures produced during catastrophic failure are higher due to particle fracture. Micro and nano-CT are used to probe this idea further, revealing that polycrystalline particles show significant damage and fracturing during failure, whereas single-crystal materials remain largely intact.Both polycrystalline and single-crystal morphologies were cycled to 80% capacity retention, with EIS and diagnostic cycles used to identify prevalent degradation modes for both particle structures. As previously found, the single-crystal cells showed superior cycle life to the polycrystalline materials3. The same combination of ARC and X-ray CT was then applied to aged cells, where it was found that aged cells show lower thermal stability than their pristine counterparts.Overall, this work aims to build understanding of the interplay between material structure, safety and degradation of nickel-rich cathodes, with the goal of informing future material development to produce batteries that are safer throughout their lifetimes. G. Qian et al., Energy Storage Mater., 27, 140–149 (2020) https://doi.org/10.1016/j.ensm.2020.01.027.X. Feng et al., Energy Storage Mater., 10, 246–267 (2018) https://doi.org/10.1016/j.ensm.2017.05.013.D. Ren et al., eTransportation, 2, 100034 (2019) https://doi.org/10.1016/j.etran.2019.100034.

Influence of sloping ground conditions on cyclic liquefaction behavior of sand under simple shear loading

An experimental program of undrained cyclic simple shear tests was undertaken on Ticino sand, covering a broad range of initial relative densities and static stress levels, to investigate the effect of an initial static shear stress on failure mechanism, cyclic resistance, and pore water pressure generation. The results indicated that two types of failure mechanisms occurred, namely cyclic mobility and plastic strain accumulation, depending on the magnitude of the initial static shear stress with respect to the applied cyclic shear stress. Test results showed that the cyclic resistance of Ticino sand may either increase or decrease with an increasing initial static shear stress depending on the density state of the sand. The Kα correction factors measured under cyclic simple shear loading were compared with the values reported in the literature based on both cyclic triaxial and simple shear tests, suggesting that Kα could be dependent on the particle gradations and grain shape for a given depositional mechanism. Finally, it was verified that the initial static shear stress has a remarkable impact on the development of cyclic pore-water pressures (PWP) of the sands so that a modified PWP generation model has been effectively proposed in the present study.

Comparisons of macrofaunal communities occupying shores across the full particle-size spectrum reveals pebble beaches to be a distinct coastal habitat type

Intertidal research has focused primarily on very fine to coarse sandy beaches (grain size <1 mm) and on rocky shores, while shores with grain sizes of 1-256+ mm have rarely been studied. Within South Africa, few published accounts describe the biota of very coarse sand (1-<2 mm), granule (2-<4 mm), pebble (4-<64 mm) or cobble (64-<256 mm) shores, and only one reports on boulder (256+ mm) shores. The objective here was to determine how many distinct habitat types occur across the full spectrum of particle sizes within this region, and what taxa characterise the biota of each habitat type. Biota from 14 shores of grain sizes 1-256 mm within the Western Cape Province (southeastern Atlantic Ocean) were sampled and compared with similar published data from 32 other regional sites with either finer or coarser grain size. Three main groupings emerged from a similarity analysis: sandy shores (of particle size <1 mm); pebble (4-<64 mm) shores; and boulder (256+ mm) plus rocky shores, with cobbles serving as a transition between those two. Sandy shores were characterised by various burrowing taxa, and boulder (>256 mm) and rocky shores mostly by grazing gastropods. Shores of 4-<64 mm particle grain size were colonised by a distinctive but previously unrecognised macrofaunal community characterised by an impoverished fauna dominated by small, mobile, mostly air-breathing arthropod taxa.

Hydrogen storage characteristics of Ti1.04Fe0.7Ni0.1Zr0.1Mn0.1Pr0.06 alloy treated by ball milling

In order to enhance the hydrogen storage performances of TiFe alloy, the Ti1.04Fe0.7Ni0.1Zr0.1Mn0.1Pr0.06 alloy was prepared through using transition metals (Ni, Mn, Zr) partially substitute Fe and rare earth Pr partially substitute Ti. The microstructure of the alloy was further adjusted by ball milling for different time. The master alloy contained TiFe, Ti2Fe and Pr phases. Ball milling treatment led to the reduction of the particle size and grain size. The master alloy (M-0 sample) and the alloys with short-time ball milling treatment (M-0.5 and M-1 samples) absorbed hydrogen immediately at the first hydrogenation cycle at 423 K and 3 MPa H2, while the alloys with long-time ball milling treatment (M-3 and M-5 samples) showed an incubation time. The M-0.5 sample not only presented the optimum activation property, but also showed the most outstanding hydriding/dehydriding kinetics and capacity. It achieved the saturated hydrogenation state within 2158 s. The hydrogenation capacity was 1.471, 1.626, 1.547, 1.485 and 1.417 wt% for the M-0, M-0.5, M-1, M-3 and M-5 samples at 313 K and 3 MPa H2, respectively. In addition, ball milling treatment caused the decrease of cell volume of TiFe phase in the samples, which reduced the thermodynamic stability of the hydrides.

Characterization and Gamma-ray Shielding Performance of Calcinated and Ball-Milled Calcinated Bentonite Clay Nanoparticles

The current investigation deals with the fabrication of two various composite-based bentonite clay minerals. The characterization and radiation shielding parameters for the two fabricated composites (calcinated and ball-milled calcinated bentonite) were studied. X-ray diffraction was utilized to illustrate the crystalline phase of the fabricated composites. Furthermore, Williamson and Hall’s method was used to determine the grain size of both the calcinated and ball-milled calcinated composites. The particle size, according to the calculation was 39.84 nm, and the strain was 0.216 for the calcinated bentonite, while the particle size of the ball-milled bentonite was 26.96 nm, and the strain was 0.219. In comparison, the transmission electron microscope (TEM) showed that the grain size of the calcinated bentonite was 566.59 nm, and it was 296.21 nm for the ball-milled calcinated bentonite. The density of the fabricated composites varied between 1.60 and 186 g/cm3 for the calcinated bentonite and between 1.83 and 2.075 g/cm3 for the ball-milled calcinated bentonite. Moreover, the radiation shielding capacity of the composites was analyzed. The results show that the gamma-ray attenuation capacity of ball-milled calcinated bentonite is high compared to ordinary calcinated bentonite. These results confirm the effect of particle grain size on optimizing the gamma-ray shielding capacity of the fabricated materials.

Microstructure evolution and densification behavior of TiC/316L composite powders during cold/warm die compaction and solid-state sintering: 3D particulate scale numerical modelling and experimental validation

To identify the microstructure evolution and densification behavior of TiC/316L composites in powder metallurgy (PM) process, 3D particulate scale numerical simulations were conducted to reproduce the cold/warm compaction and solid-state sintering of TiC/316L composite powders with corresponding physical experiments being carried out for model validation. The effects of compaction parameters and sintering temperature on the densification behavior of TiC/316L composite powders were systemically investigated. The particle deformation and morphology, stress/strain and microstructure evolutions, and grain size distribution in the whole process were characterized and compared to further illustrate the densification behavior and the underlying dynamics/mechanisms. The results show that compared with the cold compaction, the warm compaction can not only achieve higher relative density, smaller and more uniform equivalent stress, and weaker spring back effect, but also improve the friction condition among powder particles. The plastic deformation of 316L particles is the main densification mechanism during compaction. In the solid-state sintering of TiC/316L compacts, the densification is mainly indicated by shrinkage and vanishing of large residual pores along with the growth of the sintering necks, accompanied by the particle movement and growth along the boundary regions. Meanwhile, the particle displacement and grain size distribution are more uniform in the warm compacted TiC/316L component. Moreover, the equivalent (von Mises) stress in 316L particles is smaller than that in TiC particles.