Constant Shear Research Articles

Low-temperature friction experiments on ice–salt mixtures: Implications for the strength of ice plate boundaries on Europa

While recent observational studies have suggested that the ice shell on Europa is undergoing active plate subduction, some theoretical studies have concluded that the high frictional strength of ice would prevent such icy plates from subducting. Constraining the frictional behavior of mixtures of ice and non-ice materials that exist on the surface is therefore key to understanding the frictional strength of plate boundaries on Europa. Here we perform friction experiments on 1 mm thick layers of gouge comprised of mixtures of ice-Ih and magnesium chloride with 0, 17, 29.5 and 47 wt% salt under low-temperature conditions (−40 to −10 °C). The experiments are conducted using a biaxial testing machine with constant normal stresses of either 2.5 or 5.0 MPa, and a constant shear velocity of 3 μm/s. Our experimental results for pure ice and ice–salt mixtures yield steady-state friction coefficients ranging from 0.72 ± 0.02 (−39.2 ± 0.7 °C) to 0.47 ± 0.01 (−16.4 ± 0.2 °C), and 0.51 ± 0.01 (−39.8 ± 1.4 °C) to 0.10 ± 0.02 (−16.9 ± 0.5 °C), respectively. These differences in friction coefficient indicate that non-ice materials can have a significant effect on the friction coefficient along the plate boundaries on Europa. Spatial variations in the frictional strength of plate boundaries are expected to be localized near the base of the conductive layer, as the friction coefficient of the ice–salt mixture exhibits a strong temperature dependence. The observed stick–slip behavior at low temperatures in our experiments indicates the potential for occurrence of intermittent stick–slip along the shallower parts of the plate boundaries, whereas steady-state sliding occurs along the deeper parts.

Efficient physical delamination of Ti3C2Tx MXene under periodic and constant shear field of Taylor vortex flow

Employing Taylor vortex flow (TVF), we have devised an innovative technique for the delamination of MXene without using a chemical intercalant and demonstrated the enhanced optoelectronic characteristics of this delaminated MXene through their successful implementation in light emitting diode (LED). The pairwise toroidal fluid motion of TVF was induced by the rotation of the inner cylinder in the Couette-Taylor (CT) reactor. Due to periodic and constant shear field, TVF was highly efficient for the exfoliation of MXene. So, the continuous exfoliation process using CT reactor always showed 8.1 ∼ 12.5 times higher delaminated MXene (d-Ti3C2Tx) yield than that using a conventional mixing tank (MT) reactor which generated turbulent eddy flow (TEF) by impeller agitation. As such, 8.26 mgּ/mL (42.90 % of recovery ratio) of d-Ti3C2Tx was obtained in CT reactor at 1300 rpm of inner cylinder rotation speed and 24 min of mean residence time (MRT). In comparison, d-Ti3C2Tx in MT reactor at 3000 rpm of agitation speed and 24 min of MRT was 0.66 mgּ/mL (3.42 % of recovery ratio). In addition, d-Ti3C2Tx in TVF was thinner and wider than that in TEF. So, the d-Ti3C2Tx was homogeneously suspended without sedimentation and oxidation in aqueous suspension over 30 days. In addition, d-Ti3C2Tx in the TVF was applied to the transparent conducting electrode of inorganic CsPbBr3 perovskite light emitting diodes (PeLEDs). The transparent conducting oxide-free PeLED had 62.52 cd/A of maximum current efficiency and 14.48 % of maximum external quantum efficiency, which is comparable to the best performance of ITO-based inorganic CsPbBr3 PeLEDs.

Growth of Floc Structure and Subsequence Compaction into Smaller Granules through Breakup and Rearrangement of Aluminum Flocs in a Constant Laminar Shear Flow.

We have constructed an outer-cylinder-rotating Couette device for high-speed shear flow in laminar flow conditions and visualized the structure formation and subsequent rearrangement of PACl (flocculant made of aluminum hydroxide gel) and kaolinite flocs by visible light imaging. In a previous report, we analyzed the case of relatively low shear rate (G-value = 29 1/s) and confirmed that the flocculation process could be separated into two stages: a floc growth stage and a breakup/rearrangement stage. Once the large bulky flocs that reached the maximum size appeared, they rearranged and densified through structural fracture and rearrangement. In this report, this process was further investigated by conducting experiments under two different high shear rates (58 and 78 1/s) at which breakup and rearrangement became more pronounced, and three different aluminum kaolinite ratios (ALT ratios) that were over and under the optimum dosage (neutralization point by Zeta potential). Visualization results confirmed that, during the growth stage, the flocculation rate could be approximated by a scaling relationship between floc size and elapsed time, which depended on the ALT ratio. After reaching the maximum size, the floc rapidly became compact and dense following adsorption of the gel, incorporating fine fragments from erosion breakup. The over and under dosages created a lot of fragments of erosion breakup, but less so in the optimum dosage. In the optimum ALT ratio, fragments did not remain because they were incorporated into the flocs and densified, and the floc size was thought to be maintained. The floc circularity distribution peaked at around 0.6 and 1, suggesting that the flocs were spherical in shape due to erosion breakup.

Flow stability and sequence of bifurcations in a cubic cavity driven by a constant shear stress

The progressive destabilisation of the incompressible flow in a cubical cavity driven by a constant shear stress is investigated numerically. To that end, one of the square faces of the cube is subjected to a constant shear stress parallel to two opposite edges of that face. The three-dimensional steady basic flow loses its mirror symmetry through a supercritical pitchfork bifurcation leading to a pair of steady stable non-symmetric flow states that are antisymmetric to each other. Upon increase of the strength of the driving, these non-symmetric equilibria become unstable via a Hopf bifurcation resulting in two limit cycles. The bifurcations are investigated using classical linear stability analyses as well as nonlinear simulations. Upon a further increase of the driving shear stress, the limit cycles destabilise through bursts triggering a complex interplay between the unstable equilibria. The transition to turbulence resembles the Pomeau–Manneville scenario.

Analytical models for pressure-driven Stokes flow through superhydrophobic and liquid-infused tubes and annular pipes

Analytical expressions for the velocity field and the effective slip length of pressure-driven Stokes flow through slippery pipes and annuli with rotationally symmetrical longitudinal slits are derived. Specifically, the developed models incorporate a finite local slip length and constant shear stress along the slits, and thus go beyond the assumption of perfect slip employed commonly for superhydrophobic surfaces. Thereby, they provide the possibility to assess the influence of both the viscosity of the air or other fluid that is modelled to fill the slits as well as the influence of the micro-geometry of these slits. First, expressions for tubes and annular pipes with superhydrophobic or slippery walls are provided. Second, these solutions are combined to a tube-within-a circular-pipe scenario, where one fluid domain provides a slip to the other. This scenario is interesting as an application to achieve stable fluid–fluid interfaces. With respect to modelling, it illustrates the specification of the local slip length depending on a linked flow field. The comparison of the analytically calculated solutions with numerical simulations shows excellent agreement. The results of this paper thus represent an important instrument for the design and optimization of slippage along surfaces in circular geometries.

The importance of nodal plane orientation diversity for earthquake focal mechanism stress inversions

Abstract Inversions of earthquake focal mechanisms are among the most accessible and reliable methods for determining crustal stress. However, the use of this method varies widely, and the assumptions that underpin it are often violated, potentially compromising stress estimates. We investigate the consequences of violating the little-studied assumption that the focal mechanisms have diverse orientations. Our approach is to employ data-informed synthetic mechanisms, with nodal plane orientations defined by recent earthquake lineaments in the Midland Basin, western Texas, and rakes consistent with slip in the mapped stress field. Using both the traditional stress inversion method that assumes constant shear stress magnitudes on the causative faults as well as a recently published variable shear stress method, we show that low fault plane diversity can cause maximum horizontal stress ( S Hmax ) orientation and relative principal stress magnitude (faulting regime) estimates to differ markedly from the true values. This problem is compounded for catalogues with even modest amounts of noise (≤15°) or few (e.g. 20) mechanisms. Significantly, traditional approaches for quantifying uncertainty such as the bootstrap can severely underestimate the true uncertainty under these circumstances. To remedy this, we provide simple tools to quantify nodal plane orientation diversity and stress inversion reliability.

Bearing capacity of strip footings seated on unreinforced and reinforced granular layers over random homogeneous and isotropic spatially variable undrained soft clay

The bearing capacity of a footing seated directly on a soft clay foundation with constant undrained shear strength is the classical Prandtl geotechnical problem. However, a footing seated directly on an undrained clay soil is an unlikely arrangement in practice. Rather, a granular layer is used as a working platform for the construction of the footing and to dissipate the footing loads over a wider area of the clay foundation surface. This paper revisits the footing problem for the case of a footing seated directly on the clay foundation, and seated on an unreinforced and geosynthetic reinforced granular layer overlying the clay foundation. Both deterministic and stochastic numerical modelling of the bearing capacity problem using the program FLAC 2D were carried out. The relationship between the design factor of safety and probabilistic margins of safety is explored for clay foundations with random homogenous and isotropic spatially variable undrained shear strength with mean strengths from 5 to 25 kPa (very soft to soft clay). For practical target probabilistic margins of safety against exceeding a design bearing capacity, the random homogenous soil condition is shown to be the most critical case for design.

A simplified cyclic shear test for pore water pressure build-up of different soils

Pore water pressure (PWP) build-up essentially takes place in loose, water saturated, coarse-grained soils causing the reduction of effective stresses and soil stiffness (soil liquefaction). Considering the same internal structure (soil fabric), stress level, loading amplitude etc. the response of different soils to external disturbance is different. Therefore, the increase of PWP or tendency to soil liquefaction is dependent on the granulometric properties of soils. This paper reveals a simple cyclic shear test that enables the comparison of the sensitivity of PWP build-up to density changes for different sands. The presented test allows a fast installation of a soil specimen and a subsequent constant volume cyclic shearing within a short time period (ca. 30 minutes). The results successfully confirm the repeatability of the method as well as the dependence of the PWP build-up on the initial relative density and saturation degree. It is also shown that the soil fabric has an essential influence on the build-up of PWP. The method aims to allocate an index value to every tested sand and thus to quantify a sensitivity of different sands to density changes with respect to liquefaction.

Structuring gelatin methacryloyl - dextran hydrogels and microgels under shear.

Gelatin methacryloyl (GelMA) is a widely used semi-synthetic polymer for a variety of bioapplications. However, the development of versatile GelMA hydrogels requires tuning of their microstructure. Herein, we report the possibility of preparing hydrogels with various microstructures under shear from an aqueous two-phase system (ATPS) consisting of GelMA and dextran. The influence of an applied preshear on dextran/GelMA droplets and bicontinuous systems is investigated by rheology that allows the application of a constant shear and is immediately followed by in situ UV-curing of the GelMA-rich phase. The microstructure of the resulting hydrogels is examined by confocal laser scanning microscopy (CLSM). The results show that the GelMA string phase and GelMA hydrogels with aligned bands can be formed depending on the concentration of dextran and the applied preshear. The influence of the pH of the ATPS is investigated and demonstrates the formation of multiple emulsions upon decreasing the charge density of GelMA. The preshearing of multiple emulsions, following gelation, leads to the formation of porous GelMA microgels. The diversity of the formed structures highlights the application potential of preshearing ATPS in the development of functional soft materials.

Characteristics of Quasi-static and Dynamic Failure of Inconel 625 Superalloy under Simple Shear

The shear flow and failure of a superalloy Inconel 625, conceived for jet engine applications, are investigated by using a modified flat gauge shear specimen with the assistance of Digital Image Correlation (DIC). The constant strain rate shear tests were successfully performed by using a screw driven Zwick machine and a bespoke spilt Hopkinson tension bar (SHTB). Nearly all gauge section is in a uniform strain state at dynamic force equilibrium condition. The constitutive relationships and the crystallographic texture show strain rate dependence. Different from the void growth induced failure at quasi-isothermal condition, the Inconel 625 fails by adiabatic shear at high strain rates. The present shear testing provides an opportunity to study the shear flow and failure of superalloy of small structural components in turbine engine.

Frictional weakening leads to unconventional singularities during dynamic rupture propagation

Earthquakes i.e. frictional ruptures, are commonly described by singular solutions of shear crack motions. These solutions assume a square root singularity order around the rupture tip and a constant shear stress value behind it, implying scale-independent edge-localized energy. However, recent observations of large-scale thermal weakening accompanied by decreasing shear stress potentially affecting the singularity order can challenge this assumption. In this study, we replicate earthquakes in a laboratory setting by conducting stick-slip experiments on PMMA samples under normal stress ranging from 1 to 4 MPa. Strain gauges rosettes, located near the frictional interface, are used to analyze each rupture event, enabling the investigation of shear stress evolution, slip velocity, and material displacement as a function of distance from the rupture tip. Our analysis of the rupture dynamics provides compelling experimental evidence of frictional rupture driven by enhanced thermal weakening. The observed rupture fronts exhibit unconventional singularity orders and display slip-dependent breakdown work (on-fault dissipated energy). Moreover, these findings elucidate the challenges associated with a priori estimating the energy budget controlling the velocity and final extent of a seismic rupture, when thermal weakening is activated during seismic slip.

Numerical investigation on rheological and thermal performances of microencapsulated phase change material suspension (MPCMS) in microchannel

Rheological and thermal performances of microencapsulated phase change material suspension (MPCMS) in microchannel are investigated with different mass fractions, Reynolds numbers and particle size distributions. The deviations of the two-phase model and the single-phase model from experiments are also examined and compared. The solid-liquid phase change process of MPCMS is described by the effective heat capacity method. The results show that as the mass fraction Cm increases up to 30%, the MPCMS flow starts to transform from the Newtonian fluid to pseudoplastic behavior (shear rate 0–110 s−1), and the resultant performance evaluation factor (PEF) increases from 1 to 1.27. As the Reynolds number is raised from 96 to 960 (Cm = 15%), the viscosity remains nearly constant (shear rate 100–1000 s−1) flowing as a Newtonian fluid, and the PEF decreases from 1.24 to 1.14. With the particle size increasing (dp = 0.1–10 μm), non-Newtonian characteristics of the suspension become more obvious (shear rate 9300–15,000 s−1), and the PEFs are all 1.15. The average deviation of the single-phase model is 12.3% compared with the experimental data, while it is only 3.65% for the two-phase model. The results provide a reference for the optimization of MPCMS application in microchannel from a rheological perspective.

Development and validation of an automatic recording microcontroller-based pendulum impact cutter

Knowledge of rice straw bunch in respect of cutting energy is the important factor for optimization of cutting elements in straw chopping system. A micro controller-based pendulum impact cutter was developed during 2019–21 at the ICAR-Central Institute of Agricultural Engineering, Bhopal, Madhya Pradesh. The system was integrated with load cell, adjustable pendulum arm and adjustable shear and approach angle (0–30 degree) during the cutting experiment. In this study, straw bunch cutting energy at the lowest point of Node 3 was examined which is just above the ground surface. Three type of blades SMS serrated, cutter bar and SMS plain blade were used to determine cutting energy. In order to determine the cutting energy requirement of straw bunch, the mechanical and physical properties of straw were determined. The results represent that the cutting force was significantly affected by blade type, shear angle and approach angle. The minimum cutting energy for SMS serrated, cutter bar and SMS plain blade was registered as 120, 189 and 243 J, respectively among all combinations of shear and approach angle. Developed recording type pendulum impact cutter was compared with the traditional method at selected combination of shear and approach angle for all the three blades and the relative error was recorded between 4–6%. It was concluded that with increasing approach angle at constant shear angle the cutting force initially decreased up to 20 degree and rapid increase from 20 to 30 degree of approach angle. Consequently, the SMS serrated blade emerges as the preferred choice for the rotary impact cutter development, showcasing the potential of this research in advancing straw chopping technology.

A novel thixotropic structural dynamics model of water-based drilling fluids

Water-based drilling fluids find extensive application in drilling operations for the removal of drilling waste and the enhancement of drilling efficiency, owing to their remarkable thixotropic properties. Thixotropy in drilling fluids is intricately connected with the evolution of their internal structure. Most existing structural dynamics models that address thixotropy are tailored for waxy crude oils and oil-based suspensions, making it challenging to accurately characterize the rapid changes in the internal structure of water-based drilling fluids. In this study, we propose a novel structural dynamics model based on the constitutive models with both isotropic and kinematic hardening (IKH). This model elucidates the thixotropic properties and structural evolution characteristics of water-based drilling fluids by incorporating the rheological coefficient and the structural damage rate index. Through verification using constant shear rate and hysteresis loop experiments, the proposed model in this paper precisely describes the rheological behavior of water-based drilling fluids (including the phenomenon of stress overshoot), besides, faithfully depicts the distinctive thixotropic structural evolution of it.

The role of elastic instability on the self-assembly of particle chains in simple shear flow

Flow-induced self-assembly (FISA) is the phenomena of particle chaining in viscoelastic fluids while experiencing shear flow. FISA has a large number of applications across many fields including materials science, food processing, and biomedical engineering. Nonetheless, this phenomena is currently not fully understood and little has been done in literature so far to investigate the possible effects of the shear-induced elastic instability. In this work, a bespoke cone and plate shear cell is used to provide new insights on the FISA dynamics. In particular, we have fine-tuned the applied shear rates to investigate the chaining phenomenon of micrometer-sized spherical particles suspended into a viscoelastic fluid characterized by a distinct onset of elastic instability. This has allowed us to reveal three phenomena never reported in literature before, i.e.,: (I) the onset of the elastic instability is strongly correlated with an enhancement of FISA; (II) particle chains break apart when a constant shear is applied for “sufficiently” long-time (i.e., much longer than the fluids' longest relaxation time). This latter point correlates well with the outcomes of parallel superposition shear measurements, which (III) reveal a fading of the elastic component of the suspending fluid during continuous shear flows.

Modelling the thermo-mechanical behaviour of a rock joint

The CNSC, the Canadian regulator for the nuclear industry, participated in DECOVALEX-2023 Task G that focuses on the thermo (T) - hydro (H)- mechanical (M) behaviour of rock joints. Joints are omnipresent in rock masses and are planes of weakness in the host rock. When deep geological repositories (DGRs) for radioactive waste are being considered in areas where rock joints are present, the joints could be preferential pathways for radionuclide migration. Therefore, their THM behaviour must be better understood to assess the safety of the DGR. Under different possible internal and external perturbations, a joint can move by shear and dilation. If the joint crosses the emplacement area of a waste container, the heat generated from the waste can itself induce shearing of the joint. Excessive shear movement can in turn lead to failure of the container, resulting in earlier release of radionuclides. Furthermore, dilation that might accompany shear, results in an increase in the joint aperture creating a faster flow path for radionuclide transport. Mathematical models are important tools that need to be developed and employed, in order to assess joint shear and dilation under different loading conditions, such as the heat generated from the emplaced waste. The authors have developed such a mathematical model based on a macroscopic formulation within the framework of elasto-plasticity. It is verified against analytical solutions and validated against shear under constant normal load tests and thermal shearing tests of joints in granite.

Experimental investigation of laminar and turbulent displacement of residual oil film

Residual oil films on pipe walls are a common occurrence in industrial processes, and their presence can significantly impact system efficiency and performance. However, the mechanisms that govern oil film removal by an immiscible displacing fluid from the internal walls of pipes under different flow regimes, including laminar and turbulent flows, are not yet fully understood. In this study, we investigated the impact of displacing fluid flow regime, injected volume, displacement time, and wall shear stress on the efficiency of residual oil film removal in a pipe. We first verified the applicability of our developed oil film measurement method for the use in vertical pipes, and found that gravity did not significantly affect the long-term oil film removal process. We verified that our results from the laminar cases agree with the theoretical thin-film limit scaling under reasonable assumptions of constant shear stress and negligible surface tension. We then examined the displacement efficiency of residual oil film under laminar and turbulent flow regimes. Our experimental results revealed that the onset of turbulence of displacing fluid played an important role in the efficient removal of residual oil film, with an optimal range of Reynolds numbers (7000–8000) when the injected volume of displacing fluid is limited. Furthermore, we explored the combined effect of wall shear stress and displacement time on the displacement process under different turbulent flow regimes. We found that the intermediate turbulent regime was the most efficient for achieving cleaning in a limited time, while the highly turbulent regime proved to be the most effective for achieving complete cleaning over a longer time period. These findings have important implications for oil recovery and pipeline maintenance and provide valuable insights into optimizing the removal of residual oil film in pipes.

New Insight into Elastic Mechanical Properties and Anisotropies of Crystal Defect α-Quartz from DFT Calculation.

To reveal the cleavage mechanism of α-quartz in the grinding process of nonferrous metal ores, mechanical and charge properties of α-quartz crystals are investigated using the density functional theory. Based on the elastic constant matrix, the bulk and shear moduli were calculated before and after the α-quartz with oxygen atom defects. The results show that the ratios of bulk and shear moduli (B/G) were 0.87 and 0.95, respectively, which indicated that at the same stress level, it was easier to fracture without O-vacancy defects than with O-vacancy defects. The mapping surfaces indicated that the O-vacancy defect increased the bulk-, shear-, and Young's moduli, and Poisson ratio while decreasing the hardness. The anisotropy index (AL and AU) was calculated which illustrated that the O-vacancy can result in an increased anisotropy; meanwhile, the bulk anisotropy index (AB) increased strongly about two times. The anisotropy analysis shows the dominance crystal cleavage of the (011) plane in the shear stress and the dominance crystal cleavage of the (111) plane in the normal stress. The electron localization function α-quartz show that the O-vacancy defect can decrease the Si-Si length from 3.703 to 2.442 Å, which indicated that the O-vacancy formed the new covalent bonds between silicon atoms. Our work provided a systematic approach containing the mechanical, anisotropic, and electronic properties of mineral crystals to explain the cleavage behavior of crystals.

FEM simulation optimization and slab method on rotating extrusion of thin-walled round tube under constant shear friction

This research considering constant shear friction is to explore the rotating extrusion of thin-walled round tube based on FEM simulation and slab method, and compares the results of both models to realize the variations and acceptance. The effective stress, the effective strain, the velocity field, the average thickness, the extrusion force, and the extrusion torque can be obtained from this study. It reveals the average thickness obtained from rotating extrusion is more uniform than that obtained from no rotating extrusion. The FEM optimization for extrusion force can be combined with Taguchi method, the L934 orthogonal table considers the four control factors which are outer diameter to thickness ratio, frictional factor, rotating angular velocity, half die angle, and three levels. The ranking of influence factors and the optimization combination can be obtained from FEM simulation optimization. Eventually the extrusion force between FEM simulation and slab method is compared under rotating angular velocity, 0.2 rad/s, the maximum error is 10.49 % and the minimum error is -0.29%; the average error is 4.16%, so the trend is in good agreement each other. Therefore, the both models can be verified.

FEM simulation and optimization on rotating extrusion of bi-metal rod with constant shear friction

This study assuming constant shear friction adopts FEM simulation and the optimization to investigate into extrusion of bi-metal rod which consisted of Aluminum alloy (Core) and Copper alloy (Sleeve) with a rotating die taking tonto account the interface at bi-metal rod under the bonding situation. The forming characteristics, e.g. the effective stress, the effective strain, the velocity field, the extrusion force, the extrusion torque, and die stress can be gained by using FEM commercial software. The FEM optimization for extrusion force combines Taguchi method to establish the L934 orthogonal table that includes four control factors which are rotating angular velocity (ω), frictional factor at the interface of sleeve and die (m1), half die angle (α°), and inner die filet (R). The ranking of influence factors and the optimization combination can be obtained from FEM simulation to provide the reference to the industries.