Average Strain Rate Research Articles

Segmental speckle tracking strain and strain rate in stable coronary artery disease

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Northern Norway Regional Health Authority Background It is known that patients with coronary artery disease (CAD) display reduced global and regional strain and strain rate (SR). However, knowledge about segmental strain and SR in stable CAD patients is still limited. Purpose The purpose of this study was to explore whether segmental strain and SR analyses are different between patients with normal and stenotic coronary arteries among individuals with chest-pain. Methods A total of 510 patients with chest pain, referred to coronary computed tomography angiography (CCTA) and additional 102 patients with myocardial infarction (MI) were prospectively included. All patients underwent transthoracic echocardiography (TTE) with strain-rate analysis. All patients with CCTA-suspected CAD subsequently underwent invasive CAG, as well as in all MI patients. Global longitudinal strain (GLS) and average for segmental peak longitudinal strain during systole (PLS), peak systolic strain rate (PLSR S), peak early diastolic strain rate (PLSR E), post systolic shortening (PSS) measurements were analysed. Further, different cut-off values for reduced strain and SR were used to define the percentage of functionally reduced segments between patients with normal CAD (no CAD), MI, and stable CAD patients who were further treated by percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG). Results As shown in the table 1, all average segmental strain and SR parameters differed significantly between no CAD and MI groups. However, only PLSR E showed significant differences between no CAD and PCI groups . PLSR E, PLS and GLS showed significant differences between no CAD and CABG groups. The percentage of reduced segmental strain and SR showed similar results. Regarding the percentage of pathological segments at different cut-off values, PLSR E showed the most significant difference between these four groups at a cut-off value 1.5 (p < 0.001) (Figure 1). Conclusion Patients with MI or CABG display clearly reduced segmental strain and SR values. However, in patients with chest-pain, segmental PLSR E seemed to be the only indicator revealing subtle differences between patients with no CAD or those assigned to PCI. The diagnostic value of PLSR E needs to be investigated in further studies. Abstract Table 1 Abstract Figure 1

Segmental Tissue Speckle Tracking Predicts the Stenosis Severity in Patients With Coronary Artery Disease.

ObjectiveTwo-dimensional speckle tracking echocardiography (2D-STE) has been used as a diagnostic tool for coronary artery disease (CAD). However, whether vessel supplied myocardial strain and strain rate (SR) predict the severity of coronary artery stenosis in patients with CAD is unknown. This study aimed to investigate correlation of cardiac mechanical parameters in tissue speckle tracking measurements with coronary artery stenosis diagnosed by cardiac catheterization in patients with clinically diagnosed CAD.Methods and ResultsAmong 59 patients analyzed, 170 vessels were evaluated by coronary angiography and the corresponding echocardiography to quantify left ventricular myocardial strain and SR. The average longitudinal strain and SR of the segmental myocardium supplied by each coronary artery were calculated to achieve vessel myocardium strain (VMS) and strain rate (VMSR). The VMS and VMSR at each of four severity levels of stenosis showed significant differences among groups (p = 0.016, and p < 0.001, respectively). The strain and SR in vessels with very severe stenosis (≥75%, group IV; n = 29), 13.9 ± 4.3, and 0.9 ± 0.3, respectively, were significantly smaller than those of vessels with mild stenosis ≤ 25%, group I; n = 88, 16.9 ± 4.9, p = 0.023, and 1.2 ± 0.3, p = 0.001, respectively. The SR in vessels with moderate stenosis (26–49%, group II; n = 37), 1.0 ± 0.2, was significantly smaller than that in vessels with mild stenosis vessels (p = 0.021). The lower VMS and VMSR, the higher possibility of severe coronary stenosis is. The VMS and VMSR lower than 13.9 ± 4.3 and 0.9 ± 0.3, respectively predicted the severe coronary stenosis. The VMS and VMSR higher than 16.9 ± 4.9 and 1.2 ± 0.3, respectively predicted mild or no coronary artery stenosis.ConclusionsThe actual stenosis rate in catheterization demonstrates that this technique was able to assess coronary artery condition. Thus, the application of a non-invasive method of 2D-STE to evaluate and simplify diagnosis of CAD is feasible.

Dynamic Characteristics and Damage Constitutive Model of Mudstone under Impact Loading.

The mechanical response characteristics of mudstone from the ingate roadway of the west ventilation shaft in Yuandian No. 2 coal mine, Huaibei City, Anhui Province, China to dynamic loads were quantified in single- and cyclic-impact compression tests, using the split-Hopkinson pressure bar test device. The dynamic stress–strain relationships and the failure characteristics of mudstone samples under different impact loads were analyzed systematically. Considering the “rate effect” of the mudstone dynamic strength, the dynamic strength criterion of mudstone was proposed, and the dynamic damage constitutive model of mudstone was established, based on the statistical damage theory. In response to single-impact loads, with increasing impact pressure, the mudstone peak stress and strain gradually increased, and the peak stress and average strain rate increased nonlinearly. In response to cyclic-impact loads, with an increasing number of impacts, the mudstone peak stress first increased and then decreased, and the peak strain increased gradually. With increasing impact pressure, the number of impacts to the samples’ failure decreased gradually. By parameter identification and comparative analysis of the test results, the proposed dynamic damage constitutive model of mudstone was validated. The model can be used for stability analysis of roadway-surrounding rock under dynamic loads.

Experimental Study on Dynamic Mechanical Characteristics and Energy Evolution of Sandstone under Cyclic Impact Loading

In order to study the dynamic mechanical properties of the surrounding rock of roadway in deep mines with rock burst, cyclic impact compression tests of sandstone under different impact velocities were carried out by using the split Hopkinson pressure bar (SHPB) test system, and the dynamic stress-strain curves of the samples under cyclic impact loads and the relationship between energy dissipation and impact numbers were analyzed. The results show that, as the impact loading times increase, the initial elastic modulus of sandstone samples decreases, the peak stress decreases, and the peak strain increases; the average strain rate increases. The cumulative damage of sandstone samples under impact load is significantly affected by impact velocity and times. During the cyclic impact test, the reflected energy of sandstone increases with the increase of impact numbers, while the transmitted energy decreases and the absorbed energy increases; the cumulative specific energy absorption variable is introduced, and the cumulative specific energy absorption value of the samples increases with the increase of impact numbers, which can better characterize the variation of energy accumulation and dissipation of sandstone samples under cyclic impact.

Integration over discrete closed surfaces using the Method of Fundamental Solutions

The Method of Fundamental Solutions (MFS) is an established technique for solving linear partial differential equations. In this paper it is used for a new purpose: the approximation of integrals over closed surfaces from a finite set of known points and values. The MFS is used to fit an implicit surface through the surface points, where the implicit equation is chosen such that a surface integral is provided by summing the weights of the fit. From the divergence theorem, these surface integrals can be related to specific integrals over the enclosed volume. As a demonstration, we calculate the surface area, volume, centroid and radius of gyration, for three solid geometries: a sphere, a torus, and an ellipsoid. Very quick convergence to analytical results is shown. Local surface properties, such as the components of curvature, can also be obtained accurately. The drawbacks and advantages of the method are discussed, and the potential to calculate properties of constant-density rigid bodies (e.g. the moment of inertia tensor) and averages of incompressible flow fields (e.g. average flow velocity and strain rate) is highlighted.

Dynamical mechanical properties and microstructure characteristics of cemented tailings backfill considering coupled strain rates and confining pressures effects

This paper discusses the relationship between the average strain rate (ASR), confining pressure, dynamic peak compressive strength (DPCS), and cemented tailings backfill (CTB) crack volume through the SHPB test and microscopic computed tomography (CT). The CTB samples with a water-cement ratio of 1:4 and a slurry concentration of 75% were prepared to carry out SHPB tests with different ASR (25.6 ∼ 104.73 s−1), different ASR (12.16 ∼ 152.05 s−1) at different confining pressures (0.5 ∼ 2 MPa). The results show that with the increase of ASR when there is no confining pressure, the DPCS shows a trend of first increasing and then decreasing. However, when the confining pressure is 0.5 and 1 MPa, the DPCS increases linearly. When the confining pressure is 1.5 and 2 MPa, the DPCS increases exponentially and logarithmically, respectively. The micro-CT analysis shows that the total crack volume generated after the SHPB rises first and then falls with the increase of the ASR under confining pressure of 1 MPa. When the impact amplitude is 150 mV, the crack volume also decreases with the improvement of the confining pressure (0.5–2 MPa). The internal cracks of the CTB change from shear cracks to tensile cracks, and the initial pores of the samples first decrease and then increase. The failure pattern of all CTB samples by SHPB was mainly shear, tensile, and hybrid failure (shear and tensile). The research results can provide a valuable reference for the dynamic performance of CTB under confining pressure and the design of mining backfill.

Intrinsic dependence of welding quality and recrystallization on the surface-contacted micro-asperity scale during ultrasonic welding of Cu–Cu joints

Substantial shear deformation induced by high-frequency friction at the interface is inseparable from recrystallization and welding quality during ultrasonic welding. In this study, we prepared welding surfaces with various micro-asperity scales to analyze the comprehensive effects of deformation heat, shear strain and strain rate on the recrystallization and welding quality. Smaller surface-contacted micro-asperities with a size of 16.03 nm led to a surge in the low angle grain boundaries and recrystallization grains before the formation of a complete weld, which drastically increased the load carry capacity by 139% for joints welded at 1500 J comparing with larger micro-asperities. Molecular dynamics simulation indicated that weld formation involved a dynamic process, including micro-connection, tear, fracture, flattening and weld spread, and the reduction in the micro-asperity scale accelerated the flattening process and aggravated shear deformation at the intimate contact positions. According to the calculation model of recrystallization induced by the shear deformation, smaller micro-asperities promoted the coupling between high shear strain and low strain rate, and maximum shear strain of 1.57 and minimum average strain rate of 346/s were obtained simultaneously, which decreased critical recrystallization strain and enlarged the dynamic recrystallization regions during ultrasonic welding.

Investigation on surface integrity in laser-assisted machining of Inconel 718 based on in-situ observation

Inconel 718, a nickel-based superalloy, is widely used in the key parts of aero-engine owing to its high performance at elevated temperatures. Meanwhile, Inconel 718 is a typical difficult-to-cut material which is hard to obtain ideal surface integrity by conventional machining (CM). Laser-assisted machining (LAM) has a good potential to improve the machinability. In order to study the processing mechanism in the LAM of Inconel 718, the in-situ and ex-situ studies were presented in this paper. In the in-situ analysis, LAM and CM experiments were carried out based on in-situ observation and digital image correlation (DIC) technology. The Von Mises strain and equivalent plastic strain rate in the primary shear zone (PSZ) and cutting force were measured. According to the DIC results, under the experimental conditions of this paper, the average Von Mises strain and average equivalent plastic strain rate of PSZ in LAM increase by about 10% and 20% respectively due to the softening of Inconel 718 by laser heating, compared with CM. In-situ analysis shows that Inconel 718 in LAM is more prone to plastic flow, resulting in lower cutting forces. As for the ex-situ characterization, the surface roughness, residual stress and tool wear were measured. The measured results show that LAM can significantly reduce surface roughness and tool wear, and cause compressive residual stress on the machined surface.

Experimental Study on Dynamic Characteristics of Annular Coal Mine Sandstone after Different Temperatures

The rock mass is the main carrier of underground engineering. Many rock engineering involves rock mass excavation, and the temperature of deep rock mass increases with the depth rising. The study on the dynamic mechanical properties of annular coal mine sandstone under different temperatures has important guiding significance for mine excavation and rock engineering design and construction. To research the effect of high temperatures on the physical and dynamic mechanical characteristics of annular coal mine sandstone specimens, the physical parameters of the samples after the heating temperature from 25°C to 500°C were tested, and the dynamic splitting tests under the same loading condition were conducted by using SHPB test equipment. The findings indicate that with the temperature rising, the volume of samples increases, the mass and density decrease, and the change rate of the physical parameters of the annular sample is a little greater than that of the intact sample; as the temperature goes up, the dynamic tensile strength increases first and then decreases, there is a quadratic polynomial relationship with temperature; both the dynamic strain and the average strain rate decrease first and then increase as the temperature grows, showing a quadratic polynomial relationship with temperature; the damage degree of the annular and intact samples become worse as the temperature improved, and the fragments of specimen increase obviously after 200°C.

Experimental Study on Dynamic Compression Mechanics of Sandstone after Coupled Alkali‐Chemical‐Dynamic Interaction

For the purpose of analyzing the effect of the alkaline solutions on the mechanical property of sandstone impact compression, the sandstone specimens of coal mine roadway were corroded in NaOH solution with pH 7 (neutral pure water solution) and pH = 8, 9, 10, 11, and 12 for 28 d, followed by dynamic compression tests using a separated Hopkinson compression bar test device, and the microstructural changes of the specimens were measured by SEM electron microscope scanning equipment. The studies indicate that the degree of damage to the dynamic properties of a sandstone specimen is tightly correlated with the variation of the pH value of the corrosion solution. The corrosion deterioration effect of the strong alkaline solution is most obvious, followed by the weak alkaline solution, and the mechanical properties of the sandstone are relatively stable under a neutral solution. The dynamic compressive strength and dynamic modulus of elasticity of specimens decrease as a quadratic and cubic function, respectively, with the rising pH of the solution. The dynamic peak strain and average strain rate tend to increase with the increase in pH, and they are larger than those of the uncorroded specimens. As the pH of the solution rises, the impact damage of the sandstone specimens intensifies, and the average particle size of the fragments tends to decrease in a quadratic polynomial.

Effect of Deformation Heating on Microstructure Evolution During Hot Forging of Ti-6Al-4V

The effect of deformation heating on microstructure evolution during hot forging of Ti-6Al-4V was established. For this purpose, right-circular cylinders of Ti-6Al-4V with an equiaxed-α preform microstructure were preheated to a temperature between 1148 K (875 °C) and 1223 K (950 °C), and compressed to a 60-pct. height reduction in a screw press, yielding average true strain rates of ~ 5 to 20 s−1. Thermocouple measurements and corroborating finite-element-method (FEM) simulations quantified substantial deformation-heating-induced temperature increases. For all preheat temperatures, the heating transient led to an exposure above the equilibriumβ transus temperature. Despite such temperature excursions, the volume fraction of equiaxed primary α in each forged billet was only slightly lower than that in the corresponding preheated condition. The source of such observations was rationalized on the basis of the (hypothesized) solute-concentration fields that develop during the heating and cooling transients experienced in high-rate deformation processing.

Vesicle dynamics in large amplitude oscillatory extensional flow

Although the behaviour of fluid-filled vesicles in steady flows has been extensively studied, far less is understood regarding the shape dynamics of vesicles in time-dependent oscillatory flows. Here, we investigate the nonlinear dynamics of vesicles in large amplitude oscillatory extensional (LAOE) flows using both experiments and boundary integral (BI) simulations. Our results characterize the transient membrane deformations, dynamical regimes and stress response of vesicles in LAOE in terms of reduced volume (vesicle asphericity), capillary number ( ${Ca}$ , dimensionless flow strength) and Deborah number ( ${De}$ , dimensionless flow frequency). Results from single vesicle experiments are found to be in good agreement with BI simulations across a wide range of parameters. Our results reveal three distinct dynamical regimes based on vesicle deformation: pulsating, reorienting and symmetrical regimes. We construct phase diagrams characterizing the transition of vesicle shapes between pulsating, reorienting and symmetrical regimes within the two-dimensional Pipkin space defined by ${De}$ and ${Ca}$ . Contrary to observations on clean Newtonian droplets, vesicles do not reach a maximum length twice per strain rate cycle in the reorienting and pulsating regimes. The distinct dynamics observed in each regime result from a competition between the flow frequency, flow time scale and membrane deformation time scale. By calculating the particle stresslet, we quantify the nonlinear relationship between average vesicle stress and strain rate. Additionally, we present results on tubular vesicles that undergo shape transformation over several strain cycles. Broadly, our work provides new information regarding the transient dynamics of vesicles in time-dependent flows that directly informs bulk suspension rheology.

Experimental Study on Physical and Dynamic Mechanical Properties of Temperature-Water Coupled Sandstone

In order to study the influence characteristics of water bath at different temperatures on rock physical and dynamic mechanical properties, a total of 15 groups of temperature-water bath treatment were carried out on coal mine roadway sandstone at 25°C∼95°C, and the basic physical parameters were tested. The impact compression test was carried out using the split Hopkinson pressure bar (SHPB) device. The results show that, with the increase of water bath temperature, the particle gap on the specimen surface increases. The volume, mass, and density of the specimens all increased with the increase of water bath temperature, and the increase was closely related to the water bath temperature. The dynamic compressive strength increases as a quadratic function of the water bath temperature, and the rate of increase is different before and after 45°C. The dynamic peak strain and average strain rate showed a quadratic function with the water bath temperature. The dynamic peak strain before 45°C decreased with the temperature increasing, and the dynamic peak strain after 45°C increased with the temperature increasing. The dynamic elastic modulus increased first and then decreased with the increase of water bath temperature and reached the maximum at 45°C. The failure pattern of sandstone is spalling. With the increase of water bath temperature, the fracture degree of the specimen gradually decreases.

Evolution and control of deformation mechanisms in micro-grooving of Zr-based metallic glass

The evolution of deformation mechanisms with increasing depth of cut (DOC) in micro-grooving of Zr-based metallic glass was deeply investigated in this study for the first time. The micro-grooving characteristics of metallic glass were initially studied by nanoscratch test, which verified that the material removal mode abruptly changes from extrusion mode to cutting mode with increase of DOC. Based on the free-volume theory, a dynamic model coupling stress, temperature and free volume concentration was used to simulate the change of deformation characteristics with DOC. The results showed that the deformation mechanism of metallic glass is closely related to free volume flow, which is significantly affected by average strain rate and free volume flow coefficient in deformation zone and can be tuned with different DOC. Considering that free volume flow is determined by its flow coefficient and concentration, we proposed to control the deformation characteristics of metallic glass in micro-grooving by heat treatment and verified its effectiveness experimentally. • Materials removal mode of metallic glass changes with the increase of depth of cut. • The evolution of deformation mechanisms was studied using a dynamic model. • Free volume flow affects the evolution of deformation mechanisms significantly. • Deformation characteristics of metallic glass were experimentally modulated.

High strain rate response of laminated glass interlayer materials

During a blast event, the polymeric interlayer of laminated glass used in windows and curtain walls plays an essential role in protecting buildings and occupants. In this research, the dynamic constitutive behavior of ultraviolet (UV) cured one-component acrylic resin (UVEKOL-S), Polyvinyl butyral (PVB), and virgin PVB extracted from heat strengthened laminated glass panes were investigated at an average strain rate of 30–40 s−1 using impact drop-weight apparatus. An analytical procedure was developed to simulate the drop weight device and calculate the drop height required for a certain strain rate. A new technique was used to investigate the mechanical properties of PVB, and UVEKOL-S before and after the breakage of the laminated glass, including each material energy absorption capacity. The results show that both PVB and UVEKOL-S, at strain rates of 30–40 s−1, had an initial rise in strength. However, after the maximum stress point, both materials followed a noticeable difference in their response to failure. Comparing the high-strain and static results showed that the dynamic loading significantly affects the material response and the energy absorption characteristics of the interlayer materials, and subsequently, the blast response of laminated glass panels. Sufficient data was obtained from the tests to evaluate alternative approaches to modeling PVB and UVEKOL-S materials in the blast event.

Investigation on Dynamical Mechanics, Energy Dissipation, and Microstructural Characteristics of Cemented Tailings Backfill under SHPB Tests

As mining depth increases, the backfill mining method is more and more widely used in underground mines. The dynamic load generated by the blasting can affect the stability of the cemented tailings backfill (CTB). The CTB samples were prepared to conduct a test of the split Hopkinson pressure bar (SHPB) to investigate the dynamic disturbance of CTB. The present paper discusses dynamical mechanics, energy dissipation, and microstructure analysis of CTB. Micro-computer tomography (micro-CT) scanning of CTB samples after the SHPB test was performed to analyze the evolution of internal cracks. The experimental results showed that when the average strain rate (ASR) increased from 30 to 98 s−1, the dynamic uniaxial compression strength (DUCS) of the CTB showed a trend of first increasing and decreasing with the increase in ASR. The dynamic stress–strain pre-peak curve of CTB directly enters the linear elastic stage. As ASR increases, the absorbed energy of the CTB shows a trend of first increasing and then decreasing. Moreover, according to the micro-CT scanning results, the crack area of CTB accounts for about 16% of the sample near the incident bar and about 1% near the transmitted bar. The crack area ratio is exponentially related to the specimen height. These findings can provide reasonable dynamical CTB strength data selection for underground pillar mining.

Experimental Study on Stress Uniformity and Deformation Behavior of Coals with Different Length-to-Diameter Ratios under Dynamic Compression

In this study, a uniaxial impact compression test was performed on coal samples with length-to-diameter L / D ratios of 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1 using a Φ 50 mm split Hopkinson pressure bar (SHPB) test system. This study researched the stress uniformity and deformation behavior of coal samples with different L / D ratios during dynamic compression, defined the stress equilibrium coefficient ξ , proposed a new method for determining whether a sample meets the stress uniformity hypothesis, and obtained the critical L / D ratio of 0.6 and the optimal L / D ratio of 0.3 or 0.4 for coal samples to obtain the stress equilibrium. The experimental results showed that the dynamic stress-strain curve of coal had an elastic stage, a plastic stage, and a failure stage. As the L / D ratio increased, the proportion of the elastic stage to the prepeak curve of the samples declined progressively; with an increase in the L / D ratio, the peak part of the curve also changed from “sharp” to “stagnated,” while an increase in the plasticity led to strain softening. As the L / D ratio of the samples increased, the average strain rate decreased approximately as a power function, and the decreasing trend was gradually reduced from 296.49 s−1 ( L / D =0.3) to 102.85 s−1 ( L / D =1), with a reduction of approximately 65.31%. With an increase in the L / D ratio, the peak strain gradually decreased exponentially. This study concluded that the SHPB test protocol design is of a certain reference value for low-density, low-strength, heterogeneous brittle materials, such as coal.

Anisotropic swelling behaviour of unsaturated compacted GMZ bentonite hydrated under vertical stresses

Bentonite has been considered as a potential buffer/backfill material for construction of engineering barriers in deep geological repository for disposal of high-level nuclear waste. Anisotropy will be inevitably generated during static compaction during preparation of bentonite blocks, leading to induce possible influences on buffering function formation of the engineering barrier system and even the safety of the whole repository. In the present work, swelling deformation tests along the directions both perpendicular and parallel to the compaction plane were conducted on unsaturated compacted GMZ bentonite specimens using a self-developed lateral confined swelling test setup. Influences of initial dry density and vertical pressure on the final swelling strain and its anisotropy, as well as the mechanism of evolution of anisotropy coefficient on hydration, were analysed. Results demonstrate that the swelling time, average strain rate and final swelling strain increase with increasing initial dry density and decrease with increasing vertical pressure. Meanwhile, the swelling strain along the perpendicular direction is much higher than that along the parallel direction, exhibiting an obvious anisotropic swelling characteristic. The anisotropy coefficient is relatively large at the initial swelling stage, and then gradually decreases to be stabilised. The final anisotropy coefficient increases with initial dry density and decreases with vertical pressure.

Research on the Mechanical Properties and Energy Consumption Transfer Law of Cement Tailings Backfill Under Impact Load

The cemented tailings backfill (CTB), which plays a significant role in the stability of mine structure, is made of cement, tailings, and water in a certain proportion. When blasting and excavating an underground mine, the CTB will be disturbed by blasting. The impact load of blasting has an impact on the stability of the CTB, which is directly related to the safety of mine construction. The mechanical behaviour of CTB is generally affected by the cement-tailings ratio (C/T) and average strain rate (ASR). Therefore, a series of impact experiments were carried out on three CTB specimens with different C/T using a SHPB. Combined with the experimental results, this account reports studies on the effects of C/T and ASR on the mechanical properties of CTB, and on the energy transfer laws of CTB during impact compression. The research results show that when the ASR is less than 70 s−1, the peak stress and the peak strain have the same trend, and both of them continue to increase with the increase of ASR.When the ASR exceeds 70 s−1, as the ASR increases, the peak stress continues to increase, but the peak strain decreases gradually. Afterwards, the law of energy transfer of the CTB specimen was analyzed. It was found that as the incident energy increased, the energy reflection ratio of the CTB increased. Both the energy transmitted ratio and the energy dissipation ratio decreased. The volumetric energy showed a sharp increase first and then a trend Because of the slowly increasing trend. Finally, according to the failure morphology of the CTB, it is found that the ASR and the C/T together affect the failure of the CTB. The failure model of the CTB is mainly split failure and crush failure.

Dynamics of rigid particles in a confined flow of viscoelastic and strongly shear-thinning fluid at very small Reynolds numbers

Despite growing interest in the focusing and manipulation of particles in non-Newtonian fluids in confined flows, the combined effect of viscoelastic and shear-thinning effects on particle dynamics is not well understood. Herein, we report the dynamics of rigid microparticles in confined flows of strongly shear-thinning viscoelastic (STVE) fluids at very low Reynolds numbers. Our experiments with different STVE fluids reveal five different regimes: original streamline, bimodal, center migration, defocusing, and wall migration (WM), depending upon the fluid properties and flow rates. It is found that the occurrence of the different regimes depends on the STVE parameter (ψ) and average strain rate (γ̇¯). We find that the dynamics of particles in the different regimes is underpinned by the synergy between viscoelastic lift force (FVE) and shear-thinning lift force (FST). Numerical simulation results of strain rate and viscosity profiles at different ψ and γ̇¯ enable estimation of the forces and explaining the dynamics observed. We expect that our study will find relevance in applications involving positioning and manipulation of particles in confined flows of STVE fluids.