Range Of Grain Sizes Research Articles

Fingerprinting sources of beach sands by grain-size, using mid-infrared spectroscopy (MIRS) and portable XRF. Implications for coastal recovery along a tsunami-struck delta coastline

Determining modern sediment provenance along sandy beaches helps understanding coastline dynamics and can therefore assist coastal management. Provenance analysis relies usually on mineralogical, elemental, and isotopic fingerprinting of sediment sources. Mid-Infrared Spectroscopy (MIRS) offers a rapid and non-destructive alternative. It relies on the identification of molecular-bonds in organic and inorganic materials. Thus far, MIRS has been used to fingerprint fine-grained sediments in mountainous and agricultural catchments. Here we use MIRS to analyze a range of sediment grain sizes (<0.25 mm; 0.25–0.5 mm; 0.5–2 mm) in modern fluvial and coastal sands, located in the delta of the Aceh River in Sumatra. Variations in molecular bond associations are compared to variations in major element concentration, quantified by portable X-ray fluorescence (pXRF) on a subset of samples. Covariations between MIRS and pXRF data are used to predict major element concentrations in all samples. Discriminant Analysis (DA) is used to classify sand-feeding streams into groups possessing distinctive MIRS fingerprints. DA proximity relationships are then used to predict the contribution of each source group to trunk stream sand and beach sands. The best discrimination is obtained among sands belonging to the medium grain-size fraction. Simple forward modeling of the expected contributions of the different sources is used to shade light on the DA-predicted association patterns. It helps discussing the biases introduced by sediment compositional changes from the headwaters to the coast, especially hydrodynamic sorting. We find that sand composition along the delta shoreline is primarily controlled by the asymmetric dispersal of sediment from the Aceh River mouth, owing to directional longshore drift. Local variations are generated by particle-size effects and by the propensity of the coast to erode or thicken over the past century. The coastal stretches the most severely damaged by the 2004 Indian Ocean Tsunami exhibit the greatest variations in apparent provenance between sub-fractions.

Grain size effect on the recovery stress and strain of a Fe–Mn–Si shape memory alloy in a wide range of grain sizes

The grain size effect on the recovery strain and recovery stress was systematically examined over a very wide grain-size range (between 1.4 μm and 171 μm) in the Fe-15.9Mn-5.1Si-8.1Cr-3.9Ni-0.02C alloy for a better understanding of the grain size effect on shape memory properties of the Fe–Mn–Si based alloys. The recovery strain rapidly increases with grain size up to approximately 16 μm and then gradually increases with a further increase in grain size. A linear relationship between recovery strain and logd (d: grain size) is observed in the whole grain size range. The densities of grain boundaries and annealing twin boundaries also exhibit the linear relationship with logd, but the trend is opposite, suggesting that recovery strain is directly related to the densities of grain boundaries and twin boundaries and the former increases as the latter decreases. The recovery stress behavior during heating and cooling of the samples is different depending on the grain size range. When the grain size is smaller than 6 μm, yielding does not occur during sample cooling. When the grain size is in the range between 16 μm and 33 μm, yielding occurs during cooling. When the grain size is larger than 46 μm, yielding and forward martensitic transformation -occur in sequence during cooling. The highest recovery stress is obtained at a grain size of 6 μm, which is the largest grain size where yielding can be avoided during cooling, and the lowest recovery stress is obtained at a grain size of 171 μm, where both yielding and forward martensitic transformation occur during cooling. Depending on the degree of grain refinement, the quality of improvement in recovery stress and recovery strain is expected to be different. Simultaneous improvement of recovery stress and strain is predicted to be hard to effectively achieve only through grain refinement.

The influence of bedrock river morphology and alluvial cover on gravel entrainment. Part 2: Modelling critical shear stress

AbstractThe critical shear stress (τc) at which grains are entrained on a bedrock surface is important for determining how bedrock rivers evolve through changes in sediment cover and bedrock erosion. The difference in τc for grains on bedrock and alluvial surfaces also determines whether a channel may be susceptible to runaway alluviation. Bedrock channel beds can have a wide variety of morphologies, but we do not fully understand how this variation affects τc. Here we address how bedrock morphology alters the grain entrainment parameters of pivoting angle, grain exposure and roughness height z0, and thus τc. In our companion article we used scaled, 3D printed replicas of seven bedrock surfaces to measure grain pivoting angles for four grain sizes. For three surfaces, pivoting angles were also measured with 25–100% sediment cover. In this second article, we combine these pivot angle data with measurements of grain exposure and surface roughness (standard deviation of elevations, σz) to predict τc using a force–balance model. The bedrock topography produces substantial variation in τc; for a given grain diameter (D), a 3.6× range of σz across the surfaces without sediment cover produces up to a 5.1× variation in τc. For comparison, for any single surface, τc varies by up to 2.5× for a fourfold range in grain size. Comparison to previous models with less representation of grain‐scale geometry shows that in our results grains move at lower values of dimensionless critical shear stress (τ*c), and that τ*c decreases more quickly with increasing D/σz. However, direct comparison is difficult because previous relationships are based on a hydraulic roughness length that cannot be easily predicted without hydraulic data. Our results propose a new relationship between D/σz and τ*c, but further development and testing require datasets that combine measurements of flow, τc and grain‐scale geometry.

Interpretable Machine Learning Analysis of Stress Concentration in Magnesium: An Insight beyond the Black Box of Predictive Modeling

In the present work, machine learning (ML) was employed to build a model, and through it, the microstructural features (parameters) affecting the stress concentration (SC) during plastic deformation of magnesium (Mg)-based materials are determined. As a descriptor for the SC, the kernel average misorientation (KAM) was used, and starting from the microstructural features of pure Mg and AZ31 Mg alloy, as recorded using electron backscattered diffraction (EBSD), the ML model was trained and constructed using various types of ML algorithms, including Logistic Regression (LR), Decision Trees (DT), Random Forest (RF), Naive Bayes Classifier (NBC), K-Nearest Neighbor (KNN), Multilayer Perceptron (MLP), and Extremely Randomized Trees (ERT). The results show that the accuracy of the ERT-based model was higher compared to other models, and accordingly, the nine most-important features in the ERT-based model, those with a Gini impurity higher than 0.025, were extracted. The feature importance showed that the grain size is the most effective microstructural parameter for controlling the SC in Mg-based materials, and according to the relative Accumulated Local Effects (ALE) plot, calculated to show the relationship between KAM and grain size, it was found that SC occurs with a lower probability in the fine range of grain size. All findings from the ML-based model built in the present work were experimentally confirmed through EBSD observations.

Grain size dependant high-temperature hot corrosion (HTHC) degradation behavior in Alloy 617 during exposure in Na2SO4 + NaCl + V2O5 salt mixture

In the present investigation, the implication of grain size on the high-temperature hot corrosion (HTHC) response in Alloy 617 is studied. Towards this, specific thermal and thermo-mechanical processing schedules were employed to attain a wide range of grain sizes (7–70 µm), while maintaining other microstructural features like Σ3 n (n ≤ 3) boundary fraction, retained strain, and precipitate fraction nearly at constant. Subsequently, these specimens were exposed to Na 2 SO 4 + NaCl + V 2 O 5 (75 wt% + 20 wt% + 5 wt%) salt mixture at 1273 K for 24 h. Post-corrosion analyses reveal the formation of a highly porous and thick oxide scale on the as-received (AR) specimen (~32 µm), a relatively less porous and non-uniform oxide scale on the very coarse-grained specimen (~70 µm), and a homogeneous and dense Cr-rich scale on the very fine-grained microstructure (~7 µm). Such a protective scale on the very fine-grained specimen, developed due to the enhanced diffusivity of Cr, obstructs the entry of corrodents and thereby minimizes the percolation depth (~60 µm). The percolation depth is relatively higher (~130 µm) in the very coarse-grained specimen due to the development of a porous and non-uniform oxide scale. However, its percolation depth is still lower than the AR specimen (~ 305 µm), because of the reduced grain boundary area available for the diffusion of the corrosive species into the substrate. The AR specimen has exhibited the maximum percolation depth due to the simultaneous presence of fine and coarse grains, leading to the failure of both the aforementioned resistive mechanisms i.e., the accelerated formation of a protective Cr-rich scale and lesser availability of diffusion paths for the ingression of the corrosive species. • Very fine and very coarse-grained microstructures are resistant to HTHC damage. • AR specimen with inhomogeneous grain size distribution underwent maximum damage. • Grain refinement accelerates Cr-oxide formation that blocks entry of corrodants. • Grain coarsening decreases the channels for ingression of corrodants into the alloy. • Inhomogeneous grain size distribution in AR fails to activate resistive mechanisms.

Grain Size Tailoring to Control Strain Hardening and Improve the Mechanical Properties of a CoCrFeNiMn High-Entropy Alloy

An equiatomic CoCrFeNiMn high-entropy alloy was processed by severe plastic deformation followed by post-deformation annealing over a range of temperatures and times leading to a wide range of grain sizes from ~ 0.05 to ~ 70 μm. The results demonstrate there is a sharp evolution in grain size and hardness after annealing above 800 °C due to coarsening facilitated by the dissolution of precipitates together with a high rate of diffusion at high temperatures. Grain growth behavior revealed an incremental low value grain growth exponent with increasing annealing temperature together with a high value activation energy for grain growth of ~ 440 kJ mol−1. A critical grain size of ~ 2 µm is proposed in which deformation-induced twinning is suppressed during plastic deformation. Nevertheless, slip and deformation-induced twinning are deformation mechanisms occurring in samples with grain sizes above this critical value. A model is presented for engineering the grain size by controlling the annealing parameters in the fine grain size range to benefit from the advantages of deformation-induced twining in the CoCrFeNiMn alloy.

Entrainment and Transport of Well‐Sorted and Mixed Sediment Under Wave Motion

AbstractEntrainment and suspension of sediment particles with the size distribution similar to a range of natural sands were simulated with a focus on the vertical size sorting and transport dynamics in response to different wave conditions. The simulations were performed using a two‐phase Eulerian‐Lagrangian model by combining the LIGGGHTS discrete element method solver for sediment and SedFoam solver for the fluid phase. The model was first validated for a range of sand grain sizes from 0.21 to 0.97 mm having well‐sorted and mixed (bimodal) size distributions using laboratory oscillatory flow data. Three sediment bed configurations were studied under a wide range of velocity‐skewed waves with different wave intensity and skewness. It was found that the bimodal distribution having only 30% of coarse fraction and 70% of medium fraction responds similar to a well‐sorted coarse sand configuration. Sediment fluxes of the bimodal distribution were slightly higher than those of well‐sorted coarse sand because of the pronounced inverse grading in the bimodal distribution. Furthermore, for the bimodal distribution the medium fraction acted as a relatively smooth foundation underneath the coarse fraction which facilitated the mobilization of the coarser particles. Under high energy wave conditions, the smoothing feature was exacerbated and further caused the formation of plug flow where a thick layer of intense sediment flux was observed. Model results also showed that under high skewness waves, phase‐lag effect occurred in well‐sorted medium sand which caused lower net onshore sediment transport rates but the effect was significantly reduced for mixed sediments.

Magnetic characterisation of London's airborne nanoparticulate matter

Iron-bearing particulate matter produced by vehicle emissions is known to be toxic. To better quantify potential health risks, we have conducted the first magnetic study of a time-series of London's inhalable particulate matter (<10 μm, PM10), captured by three monitoring stations in central London (Marylebone Road, Earl's Court Road and Oxford Street) through 2010 and 2012. We conducted room-temperature analysis on all the samples, and a limited number of samples were analysed at both high and low temperatures. The high-temperature measurements identified magnetite as the dominant magnetic phase. The low-temperature measurements revealed high numbers of nanoparticles, which, assuming magnetite, are in the grain-size range 1–4 nm. It is estimated that as much as ∼40% of the total magnetic signal at 10 K is from particles <4 nm, that are magnetically ‘invisible’ at room-temperature and are being routinely under-estimated in room temperature-based magnetic studies. From the low-temperature measurements, the total concentration of magnetite was estimated at ∼7.5%, significantly higher than previously reported. The room-temperature magnetic data were compared with other pollution data, e.g., NOX and PM10, and meteorological data. Mass-dependent terms like the saturation magnetisation were found to display a strong correlation with NOX and PM10, indicating a common source for these pollutants, i.e., vehicle emissions. Magnetic coercivity measurements, which are independent of abundance, and provide information on grain-size, were consistent across all three sampling localities, again suggesting a major dominant source. Relatively small variations in coercivity were correlated with meteorological events, e.g., temperature and precipitation, suggesting preferential removal of larger airborne grains, i.e., >50 nm.

Characterisation of Coastal Sediment Properties from Spectral Reflectance Data

Remote sensing of coastal sediments for the purpose of automated mapping of their physical properties (grain size, mineralogy and carbonate content) across space has not been widely applied globally or in South Africa. This paper describes a baseline study towards achieving this aim by examining the spectral reflectance signatures of field sediment samples from a beach–dune system at Oyster Bay, Eastern Cape, South Africa. Laboratory measurements of grain size and carbonate content of field samples (n = 134) were compared to laboratory measurements of the spectral signature of these samples using an analytical spectral device (ASD), and the results interrogated using different statistical methods. These results show that the proportion of fine sand, CaCO3 content and the distributional range of sediment grain sizes within a sample (here termed span) are the parameters with greatest statistical significance—and thus greatest potential interpretive value—with respect to their spectral signatures measured by the ASD. These parameters are also statistically associated with specific wavebands in the visible and near infrared, and the shortwave infrared parts of the spectrum. These results show the potential of spectral reflectance data for discriminating elements of grain size properties of coastal sediments, and thus can provide the baseline towards achieving automated spatial mapping of sediment properties across coastal beach–dune environments using hyperspectral remote sensing techniques.

The Effect of Quartz Particle Size on the Frictional and Electrically Conductive Properties of Mixed Graphite–Quartz Gouges

Mature faults usually contain fault rocks with a wide range of mineral grain sizes. Despite the importance of mineral grain sizes in affecting fault slip behaviors, little is known about the potential mechanism(s). To better understand this problem, electrical conductivity measurements on synthetic carbon-bearing gouges were conducted along a fault-parallel direction under progressive fault slip. All experiments were carried out under a slip rate of 1 mm/s, a normal stress of 2 MPa, ambient temperature, and a pure N2 atmosphere. The specimens that were used were mixtures of identical 6 wt% graphite (Gr) powders and 94 wt% quartz (Qz) particles with five different particle sizes (#100–12500 mesh). As Gr has a low friction coefficient and high electrical conductivity, the approach in this study may provide a favorable opportunity to examine the relation between the evolutions of friction and shear textures. The experimental results indicated that the reduction in Qz particle sizes causes gradual segregation of the Gr powders in the skeletal frame formed by granular Qz particles, resulting in the decreased interconnectivity of the anastomosing Gr-film networks and the destruction of Gr-lubricated slip surface(s). Then, it eventually manifests as an increase in the steady-state frictional coefficient (μss) and a logarithmic decrease in the steady-state electrical conductivity (σss) for Gr-bearing specimens. Furthermore, the Gr-bearing gouges containing &amp;gt;3 μm Qz particles first develop foliated layers, and subsequent Gr films penetrate around the boundary of the Qz particles to form conductive interconnected networks during a progressive fault slip. These experimental results implied that carbonaceous materials (CMs) represented by Gr may complicate the frictional properties of fine-grained fault gouges in mature faults.

Analysis of the Aggregate Production Process with Different Geometric Properties in the Light Fraction Separator.

This article presents an analysis of separation results in a specially designed and activated light fraction separator used to remove impurities from mineral aggregates. Laboratory tests conducted on a quarter-technical scale involved performing experiments to ascertain the scope for adjusting the variable settings of the separator operating parameters. These include the frequency and amplitude of pulsation, the height of the heavy-product reception threshold, the size of water flow and variations in the grain size and shape of the feed. During the experiments, the degrees of chalcedonite and dolomite grain purification were studied within the range of grain size for the feed: (2.0–4.0 mm for small grains, 8.0–16.0 for coarse grains and 2.0–16.0 mm for a wide range of grain sizes). The effects of the separator were assessed based on the amount of organic impurities in each heavy product. In all experiments, very good results were obtained, because the percentage of impurities in the product after separation was below 1% in accordance with the assumed technological standard assumption. Regarding the obtained content of light impurities with the separator set to optimal operating parameters, the percentage of light impurities in the product content was reduced to below 0.1%, which meets the guidelines described according to applicable standards. Multi-variant analysis allowed the optimal operating ranges of the separator to be determined, producing refined aggregate in terms of grain size and shape. The final results were also linked to the performance of the device, and its model dependencies were also determined.

Electrostatic Lofting Conditions for Supercharged Dust

Electrostatic dust lofting may be a common occurrence on small bodies in the solar system, whereby the upward electrostatic force on a grain is able to overcome the surface gravity and cohesion binding it to the surface. This electrostatic lofting may serve to redistribute and transport dust across the surface of these bodies to produce features such as dust ponds and lineations found on Eros, or even to rid bodies of small particles completely. Classical models, which distribute charge evenly across a dust grain, have historically predicted electric field strengths that are insufficient to loft dust. However, recent studies have developed grain-scale charging models that account for the buildup of charge in the microcavities of regolith and assume unequal distribution of charge on a dust grain. These models predict electric field strengths orders of magnitude larger than classical models, which may explain how electrostatic dust lofting occurs on small bodies. In this paper, we compare the grain-scale supercharging models developed by Zimmerman et al. and survey how the different parameters affect grain charging—namely, charge separation, grain size, and dielectric breakdown strength. Furthermore, we investigate how each of the charging models can be used to bound initial condition requirements such as charge and velocity for dust lofting to occur on these small bodies. Initial condition requirements are examined for a range of grain sizes, regolith cohesive strengths, and small body sizes.

The effects of pH, ionic strength, and natural organics on the transport properties of carbon nanotubes in saturated porous medium

Carbon Nanotubes (CNTs) are widely utilized, and their inadvertent release into the soil and ground water systems may have detrimental environmental implications. Therefore, it is critical to comprehend the effect of several environmental conditions on the fate and transport of CNTs in porous media. In previous studies, a narrow range of pH, ionic strength, and collector grain size have only been considered while evaluating the transport and retention of functionalized multiwalled carbon nanotubes (f-MWCNTs). None have highlighted the effect of environmentally relevant concentrations of natural organic matter and particle concentrations on the mobility of f-MWCNTs in porous medium. The current study aims to fill the knowledge gap by evaluating the fate and transport of f-MWCNTs at different, environmentally relevant physicochemical conditions of pH (5, 7, and 9), ionic strengths (10, 50, and 100 mM), humic acid as representative of natural organic matter (0.1, 1, and 10 mg/L) and particle concentrations (10, 25, and 50 mg/L) through saturated porous medium (quartz sand). It was noted that a wide range of pH and humic acid imparted an overall negative charge on the particles, enhancing their mobility (C/C0 > 0.8). However, transport of the f-MWCNTs was hindered in the presence of high ionic strength and particle concentrations (C/C0 < 0.1). The transport profile was mathematically simulated using a one-dimensional advection-dispersion equation (ADE) and colloidal filtration theory (CFT). Additionally, interaction energy profiles based on the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory were estimated to gain a better understanding of the mechanism of f-MWCNT deposition. In light of the potential environmental consequences, the impact of real-world water systems (tap, river, lake, and ground water) on the transport behaviour of f-MWCNTs was also investigated. The study considerably advances our understanding of the various physicochemical and environmental factors that can critically impact the transport of f-MWCNT in porous media, which could prove beneficial for environmental applications and risk management.

Macroscopic and Petrographic Analyses of the Mortars from the Roman villa of Noheda (Villar de Domingo García, Cuenca)

The Roman villa of Noheda, located in the municipality of Villar de Domingo García (Cuenca), is one of the most important archaeological sites in Spain and one of the most important museum complexes in Europe. In recent years, several archaeological investigations have been developed (archaeometry of building materials, natural resources, ways and roads). Furthermore, various restoration and consolidation works have been carried out on structures, walls and floors. The archaeological management team requested a characterisation of the mortars found in the coatings of the walls and floors of the complex to identify differences in its production. After checking the rooms, the state of conservation of the elements and the significance of the materials used, several mortar samples were analysed by means of macroscopic techniques before applying a petrographic analysis. The results showed an interesting variety in the distribution of aggregates, a complex microstratigraphy and a range of grain sizes in the mortars from different rooms. Magnesium, silica and aluminium from limestone were found. Crushed and powdered limestone was used as an aggregate with irregular distribution. Calcite nodules were observed as evidence that the mortar had been poorly mixed in preparation.

Predictions on the Phase Constitution of SmCo7-XMx Alloys by Data Mining.

Based on a home-built Sm-Co-based alloys database, this work proposes a support vector machine model to study the concurrent effects of element doping and microstructure scale on the phase constitution of SmCo7-based alloys. The results indicated that the doping element’s melting point and electronegativity difference with Co are the key features that affect the stability of the 1:7 H phase. High-throughput predictions on the phase constitution of SmCo7-based alloys with various characteristics were achieved. It was found that doping elements with electronegativity differences with Co that are smaller than 0.05 can significantly enhance 1:7 H phase stability in a broad range of grain sizes. When the electronegativity difference increases to 0.4, the phase stability becomes more dependent on the melting point of the doping element, the doping concentration, and the mean grain size of the alloy. The present data-driven method and the proposed rule for 1:7 H phase stabilization were confirmed by experiments. This work provides a quantitative strategy for composition design and tailoring grain size to achieve high stability of the 1:7 H phase in Sm-Co-based permanent magnets. The present method is applicable for evaluating the phase stability of a wide range of metastable alloys.

Uncertainty in Grain Size Estimations of Volatiles on Trans-Neptunian Objects and Kuiper Belt Objects

Abstract We analyze the uncertainty in grain size estimation of pure methane (CH4) and nitrogen saturated with methane (N2:CH4) ices, the most abundant volatile materials on trans-Neptunian objects (TNOs) and Kuiper Belt objects (KBOs). We compare the single scattering albedo, which determines the grain size estimation of outer solar system regolith, of these ices using the Mie scattering model and two other Hapke approximations (Hapke 1993) in radiative transfer scattering models (RTMs) at near-infrared (NIR) wavelengths (1–5 μm). The equivalent slab (Hapke slab) approximation model predicts results much closer to Mie scattering over the NIR wavelengths at a wide range of grain sizes. In contrast, even though the internal scattering model predicts an approximate particle diameter close to the Mie model for particles with a 10 μm radii, it exhibits higher discrepancies in the predicted estimation for larger grain sizes (e.g., 100 and 1000 μm radii). Owing to the Rayleigh effect on single-scattering properties, neither Hapke approximate models could predict an accurate grain size estimation for the small particles (radii ≤5 μm). We recommend that future studies should favor the Hapke slab approximation when employing RTMs for estimating grain sizes of the vast number of TNOs and KBOs in the outer solar system.

Size effect on the martensitic transformation of Ti–Nb shape memory alloy

The effect of grain size on martensitic transformation was investigated by transmission electron microscopy in a nanocrystalline Ti–16Nb thin film with a broad range of grain sizes. The results show that the larger nanocrystals are filled with multiple variants with the {111}α" type I twinning relationship. As the grain size decreases to about 40 nm, the martensite changes to the single variant morphology, and the shape memory effect is believed to deteriorate significantly then. Finally, the martensitic transformation is totally suppressed and the β parent remains when the grain size drops below 25 nm.

Liquefied sites of the 2012 Emilia earthquake: a comprehensive database of the geological and geotechnical features (Quaternary alluvial Po plain, Italy)

This paper presents a comprehensive geological and geotechnical study of the whole area affected by liquefaction following the 2012 Emilia earthquakes, including all the available information from the field reconnaissance surveys, in situ tests, and laboratory analyses. The compilation was performed at 120 liquefied sites to verify and validate the reliability of liquefaction charts in alluvial sediments, and to assess liquefaction induced by the 2012 seismic sequence in the Emilia plain. The results reveal a wide range of grain sizes (from clean sands to sandy silts) and compositional characteristics (quartz-rich to litharenitic) in the 2012 ejecta, and show a strong relationship between the liquefaction and stratigraphic architecture of the subsurface. The availability of in situ tests at the liquefied sites makes it possible to verify and validate the reliability of the liquefaction charts in alluvial sediments with respect to the real observations. For the analyzed Emilia case studies, the use of non-liquefiable crust provides better estimations of the liquefaction manifestations when coupled with the thickness of the liquefiable layer rather than with the liquefaction potential index. Altogether, this work makes available to the international scientific community a consistent liquefaction database for in-depth earthquake studies.

Effect of twinning deformation on work hardening in commercially pure titanium

To clarify the effect of twinning deformation on the work-hardening behavior of commercially pure titanium, the changes in the grain size and texture due to twinning deformation were investigated, along with the grain-size dependence of the work-hardening behavior. In specimens with an average grain size of 10 μm or less, twinning deformation was inactive, and the instantaneous work-hardening exponent (n = d(lnσ)/d (lnε)) was constant at approximately 0.2. For specimens in which twinning deformation occurred, the average grain size decreased and the texture changed with increasing strain due to twinning deformation, which resulted in an increase in the instantaneous n value. In the grain-size range at which twinning deformation did not occur, the smaller the grain size, the higher the rate of increase in the dislocation density and the greater the activity of ⟨c + a⟩-type dislocations, resulting in an increased strain hardening rate. Furthermore, the flow stress could be approximated using only the Bailey–Hirsh equation. The promotion of work hardening by twinning deformation can be mostly explained by the increase in the dislocation density increment rate, increase in the fraction of ⟨c + a⟩ dislocation due to grain refinement, and change in the Taylor factor due to the change in the texture.

Measuring the grain‐size distributions of mass movement deposits

AbstractMass movement deposit grain‐size distributions (GSDs) record initiation, transport and deposition mechanisms, and contribute to the rate at which sediment is exported from hillslopes to channels. Defining the GSD of a mass movement deposit is a significant challenge because they are often difficult to access, are heterogeneous in planform and with depth, contain grain sizes from clay (&lt;63 μm) to boulders (&gt;1 m), and require considerable time to calculate accurately. There are numerous methods used to measure mass movement GSDs, but no single method alone can measure the entire range of grain sizes. This paper compares five common methods for determining mass movement deposit GSDs to assess how their accuracy may affect their applicability to different research areas. We applied an automated wavelet analysis (pyDGS), Wolman pebble counts, survey tape counts, manual photo counts and sieving to three different mass movement deposits (two debris flows, one rockslide) in Tredegar, Wales and the Longmen Shan, China. We found that pyDGS and survey tape counts produced comparable GSDs to sieving over a single order of magnitude. PyDGS required calibration to achieve accurate results, limiting its use for many applications. In Tredegar, Wolman pebble counts over‐estimated grain sizes in the lower 80% of the distribution relative to the other four methods used. We demonstrate that method choice can introduce significant uncertainties, particularly at the edges of the distributions, such that D16 values differ by up to a factor of five. These methodological uncertainties limit GSD comparisons across studies, particularly where these are used to infer processes within deposits. To minimize these challenges, the methods chosen should be both carefully reported and consistent with the research question.