Constant Shear Research Articles

Influence of mixed particle sizes on shear yield stress of magnetorheological fluid

AbstractThis study investigated the effect of magnetic particle size and volume fraction on the shear yield stress and dynamic viscosity of magnetorheological fluids. Magnetorheological fluids with varying volume fractions of micro‐ and nanoscale magnetic particles were prepared. A plate‐on‐plate shear test bench was constructed to evaluate the fluids under a constant shear rate, with the applied current ranging from 0 A to 1.2 A. Results indicated that the shear yield stress initially increased and then decreased as the volume fraction of magnetic nanoparticles increased, reaching a maximum of 47 kPa at a volume fraction of 7 %. However, the excessive addition of magnetic particles or large‐diameter particles led to settling and reduced stability of the fluids. The findings suggest that optimizing the size and volume fraction of magnetic particles is crucial for maximizing the shear yield stress of magnetorheological fluids.

How inaccurate offshore wind observations impact the quality of operational numerical weather prediction

AbstractAt Norwegian offshore platforms, wind speed is observed at heights between approx. 35 and approx. 150 m a.s.l. These observations are used to estimate 10‐m wind speed, by a power law with a constant wind shear coefficient. The resulting 10‐m wind speed is then distributed to the Global Telecommunication System (GTS) and used for assimilation and verification purposes by the meteorological community. However, multiple methods with varying results exist for the reduction of wind speed from the original measurement height to 10 m. The resulting estimate of 10‐m wind speed is therefore sensitive to the choice of method. The use of such observations may therefore be suboptimal in forecast analysis and make the forecast verification difficult to interpret. This study investigates how the use of these observations impacts forecasts from the operational regional forecast system used at MET Norway and the Global Integrated Forecast System operated by ECMWF for the period 2017–2023. Both forecast systems assimilated the observations over major parts of the period and the presented results indicate that the use of these observations increased the initial errors in the forecasts. This is confirmed in a data denial experiment over a shorter period of time. The verification results show that both forecast systems underestimate the wind speed at the original measurement heights, while the results for 10‐m verification vary with the interpolation method between original sensor height and 10 m. The forecasts show in general more wind than the GTS‐distributed estimates and are in better agreement with more advanced interpolation methods. The verification results show a strong dependency on the vertical stability of the atmosphere. The major differences between the forecast systems are that the regional system shows less bias, while the standard deviations of the errors are slightly lower in the global system.

Single shot radial constant shearing interferometry with axicon using Polarization camera

Single shot radial constant shearing interferometry with axicon using Polarization camera

Identification of coulomb and constant shear frictions in hot aluminum forming by using warm and hot upsetting sliding test

Identification of coulomb and constant shear frictions in hot aluminum forming by using warm and hot upsetting sliding test

Dynamic Evolution of Local Atomic Environments in a Cu66Zr34 Bulk Metallic Glass

This study presents a molecular dynamics (MD) investigation of the evolution of local atomic environments (LAEs) in a Cu66Zr34 bulk metallic glass (BMG), both at rest and under constant shear deformation. LAEs were characterized using Voronoi polyhedra analysis. Even in the absence of external load, LAEs frequently transformed into one another due to short-ranged atomic position fluctuations. However, as expected, each transition from one polyhedra to another was balanced by the reverse transition, thereby preserving the proportions of the different polyhedra. Cu-centered icosahedral LAEs were observed to preferentially transform into and from <1,0,9,3,0>, <0,1,10,2,0>, and <0,2,8,2,0> LAEs. Upon applying pure shear, the simulation box was first deformed in one direction up to a strain of 25% and then in the opposite direction to the same strain level. Shear deformation induced large nonaffine atomic displacements in the directions parallel to the shear, which were concentrated in specific regions of the BMG, forming band-like regions. From the onset, shear deformation led to the destabilization of Cu-centered icosahedral LAEs, as indicated by more frequent transitions to and from other polyhedra. Unlike other Cu-centered LAEs, icosahedra were also found to be more sensitive to yielding. The destruction of Cu-centered icosahedra was primarily a result of net transformations into <1,0,9,3,0> and <0,2,8,2,0> LAEs in the BMG subjected to pure shear, with a minor contribution of transformations involving the <0,1,10,2,0> polyhedra.

Instability and deformation behaviors of root-reinforced soil under constant shear stress path

Climate change is becoming a greater global challenge, leading to more frequent and intense extreme weather events, which in turn increase mountain hazards like shallow landslides and soil erosion. Ecological slope protection using vegetation has gained in- creasing attention to mitigate natural disasters in recent years. While numerous studies have demonstrated the contribution of root systems to soil reinforcement, the comprehensive impact of roots on soil mechanical response under rainfall scenarios remains elusive. This study investigates the instability and deformation behaviors of root-reinforced soil through constant shear drained (CSD) tests. The role of root characteristics, including biomass, diameter, and length, in modulating the shear strength, instability and deformation behaviors of soils is investigated. The results indicate that the shear strength and stability of root-reinforced soil, as well as the inhibition effect of root on contractive deformation after the initiation of instability, increasing with greater root biomass and length and smaller root diameter. Moreover, due to the potential weak interfaces, fine or stiff long roots appear to increase the likelihood of volumetric dilation in root-reinforced soil at the later stage of unstable deformation. However, this dilatancy can be effectively resisted by increasing root planting density to form the root network. Furthermore, our experiments suggest that herbaceous vegetation with finer and longer roots is more effective in mitigating static liquefaction of soils induced by rainfall infiltration. This study helps develop a predictive constitutive model for root-reinforced soils and supports future bioengineering slope design.

Mechanical Response of Mine Tailings under Constant Shear Drained Loading

Mechanical Response of Mine Tailings under Constant Shear Drained Loading

Behaviour of sand under the constant shear drained stress path: the role of fines

This paper presents a specifically designed experimental study aimed at exploring the role of fines in altering the behaviour of sand under the constant shear drained (CSD) stress path. The novelty of this study includes that the interplay of several key factors (fines shape, fines content, void ratio) was investigated systematically and the true constant shear stress condition was fulfilled by means of an advanced servo system which allowed the entire loading response to be captured. One of the marked findings is that the presence of fines not only alters the onset of instability of loose sand but also affects the deformation development thereafter. Drained instability can be triggered more easily in loose sand mixed with silica fines compared with the sand on its own. At the same quantity of fines, instability can be triggered more easily for sand mixed with rounded fines. However, the effect of fines appears to be marginal for sand at dense state. For all tested specimens, values of the axial strain rate at instability fall in a narrow range (0.008%/min–0.016%/min), meaning that the axial strain rate can be potentially a useful guide for quantitatively determining the inception of instability under the CSD conditions. The stress ratio q/p′ at onset of instability under the CSD conditions is also state dependent as under the undrained conditions.

The complex rheological behavior of a simple yield stress fluid

Concentrated emulsions and foams and microgels are comprised of deformable particles making these materials display complex rheological behavior that includes a yielding transition from an elastic solid to viscous fluid. Most studies of this class of soft matter involve shear flows and only a few report both shear and normal stresses. Here, we report measurements of the shear stress and two normal stress differences for a Carbobol microgel, which is usually classified as simple yield stress fluid, subjected to constant shear rate flows. Similar to our previous study, the shear stress evolves through the yield point in a manner indicative of simple yield stress fluid behavior while the normal stress differences evolve in a reproducibly chaotic manner. We also find that the evolution of the stresses is dependent on the whether the microgel has been in a state of relaxation or recovery prior to the measurement.

Experimental study on shear mechanical properties of concrete joints under different unloading stress paths

In order to study the shear mechanical properties of rock joint under different unloading stress paths, the RDS-200 rock joint shear test system was used to carry out direct shear tests on concrete joint specimens with five different morphologies under the CNL path and different unloading stress paths. The unloading stress paths include unloading normal load and maintaining constant shear load (UNLCSL), unloading normal load and unloading shear load (UNLUSL), unloading normal load and increasing shear load (UNLISL). The results show that the peak shear strength, cohesion, internal friction angle, pre-peak shear stiffness and residual shear strength of concrete joints under CNL path increases with the increasing JRC and normal stress. Under the UNLCSL path, under the same initial shear stress τ1, instability normal stress σi decreases with the increasing JRC, and normal stress unloading amount Δσn increases with the increasing JRC. Under the same JRC, σi increases with the increase of τ1, and Δσn decreases with the increasing τ1. Under the same JRC and σi, τi is significantly smaller under the UNLCSL path than the CNL path. Under the same JRC, the cohesion under the UNLCSL path is less than the CNL path, and the internal friction angle is higher than that the CNL path. Under the same JRC and σi, τi is the largest under the path of CNL and UNLISL, followed by the UNLCSL path, and τi under the UNLUSL path is the smallest. Compared with the CNL path, the variation range of the specimen internal friction angle is within 3% while the average decrease percentage of the specimen cohesion reaches 37.6% under the UNLCSL path, UNLISL, and UNLUSL. Therefore, it can be inferred that the decrease in cohesion caused by normal unloading is the main reason for the decrease in joint instability shear strength. After introducing the correction coefficient k of cohesion to modify the Mohr-Coulomb criterion, the maximum average relative error after correction is only 3.5%, which is significantly improved compared with the maximum average relative error of 56.9% before correction. The research conclusions can provide some reference for the accurate estimation of shear bearing capacity of rock joints under different unloading stress paths, which is of great significance to the stability evaluation and disaster prevention of rock mass engineering.

Instability of binary mixtures subjected to constant shear drained stress path: Insight from macro and micro perspective

AbstractLoose granular materials may also exhibit instability behaviors similar to liquefaction under drained conditions, commonly referred to as diffuse instability, which can be studied through constant shear drained (CSD) tests. So far, the research on CSD in binary mixtures is still insufficient. Therefore, a series of numerical tests using the discrete element method (DEM) were conducted on binary mixtures under CSD path. The possible model of instability is categorized into type I and type II, type I instability occurs prior to reaching the critical state line (CSL), whereas type II instability occurs after exceeding the CSL. The study analyzes the macroscopic instability behavior and the impact of fine content (FC) on macroscopic instability behavior. The numerical results show that as FC increases, the slope of the instability line (IL) increases initially and then falls in the p‐q plane. In the e‐p plane, the IL decreases initially and then ascends. The instability type of the binary mixtures is influenced not only by relative density but also by FC. The stability index increased first and then decreased with the increase of FC. The microscopic origin of binary mixtures instability is explored by investigating the fabric‐stress relationship. The collapse of the weak contact sub‐network triggers the specimen instability, while the strong contact sub‐network dictates the difficulty of achieving instability. FC influences the evolution of fabric anisotropy of the strong and weak contact networks, thereby controlling the macroscopic instability behavior of binary mixtures.

On the rheological properties of silica – Polyethylene oxide dispersions: Shake gels I the effect of polymer concentration and temperature

Shake-gels are aqueous mixtures of silica and Poly(ethylene-oxide) (PEO) that form reversible gels when subjected to an applied force, such as shaking. This shear-thickening effect can be observed using a rheometer, which shows discrete, sudden changes in the material's viscosity. Preliminary qualitative investigations have shown that the gelation time varies depending on the conditions used. We also measure the time required for the gel to relax and revert to its liquid state. To quantify the relationships between these variables and better understand the process and kinetics, a systematic investigation was conducted, focusing on the effects of polymer concentration and temperature on gelation and relaxation times. Experiments were carried out using a rheometer with double-gap concentric cylinder geometry, applying a constant shear rate to samples with varying polymer concentrations and temperatures. The results showed that, at a fixed shear rate, gelation and relaxation times varied significantly, ranging from a few seconds to over an hour. Both gelation and relaxation occurred more rapidly as polymer concentration increased. Additionally, higher temperatures led to faster gelation and relaxation times and vice versa.

On the rheological properties of Silica – Poly(ethylene-oxide) dispersions: "Shake gels" III The effect of salt concentration

The investigation focused on the rheological impact of sodium chloride and calcium chloride on PEO silica water mixtures, specifically studying their gelation/shear thickening behaviour referred to as "shake gels". Monitoring viscosity over time at a constant shear rate revealed a significant increase in viscosity by several orders of magnitude at a specific time point. Interestingly, higher concentrations of sodium chloride and calcium chloride correlated with shorter times required for gel formation.Following gel formation, dropping the shear rate facilitated the observation of the gel's relaxation back into a liquid state. Notably, higher concentrations of sodium chloride or calcium chloride resulted in slower relaxation processes. Furthermore, a notable difference emerged: at a consistent shear rate, calcium chloride exhibited faster gelation compared to sodium chloride, while during relaxation, calcium chloride relaxed at a slower pace than sodium chloride. This behaviour can be attributed to the effect of salt on polymer molecules. The presence of salt results in reduction in Debye length and polymer gets contracted. Consequently, shearing becomes more easier even though at lower shear rate as salt concentration increases. In contrast, during the relaxation process, polymer restructuring is hindered due to electrostatic repulsion and Debye length decreases, resulting in slower relaxation as salt concentration increases. The variations in gelation and relaxation behaviour between different salts can primarily be attributed to the differing ionic strengths exhibited by these salts.

Hygrothermal effect of bio-inspired helicoid laminate plate for strengthening damaged RC beam

This study investigates the influence of moisture and Thermo-hygroscopic influence on bio-inspired helicoidally laminated composite plates (BHLC) for strengthening damaged reinforced concrete (RC) beams. Borrowing inspiration from nature’s design principles, BHLC plates represent a novel approach to rehabilitation. An analytical approach based on deformation compatibility is employed, assuming constant shear and normal stresses across the adhesive layer within the framework of linear elasticity. BHLC plates are implemented to restrict crack propagation within the RC beam. The analytical methodology considers equilibrium and deformation compatibility across all components: the concrete beam, BHLC plate, and adhesive layer. A parametric study explores the sensitivity of interfacial stresses to parameters such as laminate and adhesive stiffness, plate thickness, and helicoidal layup configuration. The results reveal a significant influence of these factors on the magnitude of maximum interfacial shear and normal stresses. This study establishes a foundation for future analyses of damaged RC beams strengthened with BHLC plates, potentially leading to advancements in rehabilitation methodologies and improved crack propagation modeling in RC beams.

Clot Accumulation in 3D Microfluidic Bifurcating Microvasculature Network.

The microvasculature, which makes up the majority of the cardiovascular system, plays a crucial role in the process of thrombosis, with the pathological formation of blood clots inside blood vessels. Since blood microflow conditions significantly influence platelet activation and thrombosis, accurately mimicking the structure of bifurcating microvascular networks and emulating local physiological blood flow conditions are valuable for understanding blood clot formation. In this work, we present an in vitro model for blood clotting in microvessels, focusing on 3D bifurcations that align with Murray's law, which guides vascular networks by maintaining a constant wall shear rate throughout. Using these models, we demonstrate that microvascular bifurcations act as sites facilitating thrombus formation compared to straight models. Additionally, by culturing endothelial cells on the luminal surfaces of the models, we show the potential of using our in vitro platforms to recapitulate the initial clotting in diseases involving endothelial dysfunction, such as Thrombotic Thrombocytopenic Purpura.

Double-gap bicone magnetorheology in steady shear under homogeneous magnetic and flow fields

We design, fabricate, and test a double-gap bicone magnetorheological (MR) device to measure steady shear rheological properties of MR fluids under saturating magnetic fields (i.e., large enough to saturate the MR fluids). The device is optimized using finite element method and computational fluid dynamics simulations so that homogeneous, saturating field strengths are reached while keeping a constant shear rate within the main shearing gaps. Experiments demonstrate that the flow curves in the saturation regime can be fitted to a viscoplastic Casson model in good agreement with MR fluids under much lower (nonsaturating) fields. Moreover, yield stress data follow a linear dependence on volume fraction at low particle loadings, in agreement with existing theoretical models. Published by the American Physical Society 2024

El Gordo needs El Anzuelo: Probing the structure of cluster members with multi-band extended arcs in JWST data

Gravitational lensing by galaxy clusters involves hundreds of galaxies over a large redshift range and increases the likelihood of rare phenomena (supernovae, microlensing, dark substructures, etc.). Characterizing the mass and light distributions of foreground and background objects often requires a combination of high-resolution data and advanced modeling techniques. We present the detailed analysis of a prominent quintuply imaged dusty star-forming galaxy ($ mainly lensed by three members of the massive galaxy cluster ACT-CL\,J0102$-$4915, also known as d =0.87$). We leverage JWST/NIRCam images, which contain lensing features that were unseen in previous HST images, using a Bayesian, multi-wavelength, differentiable and GPU-accelerated modeling framework that combines (lens modeling) and (field model and inference) software packages. For one of the deflectors, we complement lensing constraints with stellar kinematics measured from VLT/MUSE data. In our lens model, we explicitly include the mass distribution of the cluster, locally corrected by a constant shear field. We find that the two main deflectors (L1 and L2) have logarithmic mass density slopes steeper than isothermal, with $ L1 and $ L2 We argue that such steep density profiles can arise due to tidally truncated mass distributions, which we probe thanks to the cluster lensing boost and the strong asymmetry of the lensing configuration. Moreover, our three-dimensional source model captures most of the surface brightness of the lensed galaxy, revealing a clump with a maximum diameter of $400$ parsecs at the source redshift, visible at wavelengths $ rest mu m. Finally, we caution on using point-like features within extended arcs to constrain galaxy-scale lens models before securing them with extended arc modeling.

Peak and Residual Shear Interface Measurement between Sand and Continuum Surfaces Using Ring Shear Apparatus

This study uses a ring shear apparatus to measure the interface shear stress between five types of sand and three surfaces: steel, PVC, and stone. Experiments were conducted under normal stresses of 25, 50, and 100 kPa at a constant shear rate of 0.5 mm/min. The research examines the impact of various sand properties, including particle size distribution, median particle size, particle shape, and initial density, as well as the surface roughness and hardness of continuum materials. The results show that interface shear strength is significantly influenced by the mechanical interlock between sand particles and surface asperities, which is affected by the normalized roughness and hardness of the materials. Machine learning models, including Multiple Linear Regression and Random Forest Regression, were used to predict peak and residual shear strengths, demonstrating high accuracy. Additionally, an empirical equation was generated using eight input parameters, considering the peak and residual interface shear strength as outputs.

Experimentation, identification, and simulation of polymer swelling at extrusion die outlets

AbstractThe behavior of polyamide PA12 melt extrudates at die outlets is modeled to determine swelling process and rate. It is assessed as a function of imposed input parameters, process parameters, and die geometries. The modeling is carried out using Comsol Multiphysics® platform to simulate the swelling; in particular, its progression in time is investigated for different extrusion process parameters. The experimental swelling observed in extrusion lines tests is compared with the Tanner and Carreau‐Yasuda rheological models. A database is built up with all experiments carried out; the comparison between numerical and experimental results shows close agreement. A parametric analysis of the experimental and numerical swelling is performed. It confirms the important role of the die diameter on swelling rate, independently of shear rate. Increase in temperature lowers swelling rate at constant shear rates and geometric aspect ratio of the dies.Highlights Experimental and numerical study of polymer swelling at capillary die outlets. Behavior of PA12 polymer extrudate modeled to determine its swelling. Rheological models implemented to simulate the swelling phenomenon. Simulation results validated with experimental tests for two millimetric dies. Influence of die geometrical parameters investigated and justified.

Mechanical behavior of calcareous tuff and coal mine tailings mixture as an embankment material for road construction

The construction of embankments requires available and suitable material that sounds to the imposed load. The selection of materials that provide slope stability and maintain pavements is made through specific test control. This research aims to analyze the mechanical behavior of a mixture of 75% calcareous tuff and 25% coal mine tailings (CMTs) used on embankment foundations. the impact of particle size characteristics and the compaction on the mechanical behavior of the mixture are studied. The direct shear test was conducted on different material states, granular and uncompressed states, compaction at the Maximum Practical Optimum (MPO), and MPO compaction post a 30-day curing period at 40 degrees Celsius. the normal stress applied ranging from 50 to 500 KPa, with a constant shear rate displacement of 0.5 mm/min. The results show a substantial influence of compaction on both friction angle (φ) and cohesion (C) values. a remarkable increase in cohesion values after the curing period, attributed to the cementitious compound formation from the interaction between calcareous tuff and coal mine tailings. This investigation emphasizes coal mine tailings potential as a sustainable and cost-effective embankment material for road construction, especially in arid regions. The material exhibits significant shear strength, with a marked increase in cohesion values post-curing state. These results are conducted to consider coal mine tailings as an appealing alternative to traditional materials of road engineering.