Transient Shear Research Articles

Dynamic quantitative visualization of transient shear stresses in solids

To aid in shear strength analysis, a technique combined with a time-resolved imaging scheme to achieve direct dynamic quantitative visualization of the distribution and evolution of transient shear stresses in solids through one measurement is studied. By modulating the polarization state of the elliptically polarized light transmitted or reflected from the sample, this method requires only one measurement to achieve visualization. Mathematical models of the correlation between the variation of modulated light field and the shear stresses in the plane perpendicular to the optical axis are established based on the theory of mechanics and photoelasticity. The maximum shear stresses of any section are further derived. As an example, the distribution and evolution of shear stresses induced by an ultrasonic field have been quantitatively visualized by the technique. The visualization results are in fairly good agreement with the finite element simulation results. The simplicity and efficiency of this technique are embodied in the fact that one single measurement can directly obtain the distribution of shear stresses in solids, and the measurements of dynamic shear stresses can be conveniently realized through continuous monitoring.

Role of Ultrasound Methods for the Assessment of NAFLD.

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide. The prevalence in patients with type 2 diabetes mellitus is between 55–80%. The spectrum of NALFD ranges from simple steatosis to aggressive steatohepatitis with potentially progressive liver fibrosis up to cirrhosis and hepatocellular carcinoma. In clinical practice, there are two important aims: First to make the diagnosis of NAFLD, and second, to identify patients with advanced fibrosis, because extent of fibrosis is strongly associated with overall mortality, cardiovascular disease, hepatocellular carcinoma, and extrahepatic malignancy. Histology by liver biopsy can deliver this information, but it is an invasive procedure with rare, but potentially severe, complications. Therefore, non-invasive techniques were developed to stage fibrosis. Ultrasound is the primary imaging modality in the assessment of patients with confirmed or suspected NAFLD. This narrative review focus on different ultrasound methods to detect and graduate hepatic steatosis and to determine grade of fibrosis using elastography-methods, such as transient elastography and 2-dimensional shear wave elastography in patients with NAFLD. Particular attention is paid to the application and limitations in overweight patients in clinical practice. Finally, the role of B-mode ultrasound in NAFLD patients to screen for hepatocellular carcinoma is outlined.

Transient waves in a piezomagnetic half-space subjected to dynamic anti-plane loading

Propagation of transient waves in a piezomagnetic half-space, which is subjected to dynamic anti-plane-concentrated line force, is analyzed theoretically in this study. By employing Laplace transformation and Cagniard de-Hoop method, explicit closed forms of solution for the transverse displacement, shear stress, magnetic potential, and induction are obtained, and contribution from the mechanical and magnetic waves is thus expressed in the transient full-field solution. Propagation of the transient waves in the piezomagnetic half-space is then discussed in detail using numerical calculation. The results show that the magneto-mechanical coupling coefficient and location of the receiver have a significant influence on the transient response of this half-space. The magnitude of the transient shear stress is effectively reduced by the weakening magneto-mechanical coupling coefficient and the arrival time of the transient magnetic induction peak increases with decreasing magneto-mechanical coupling coefficient. In addition, it is found that the smaller the magneto-mechanical coupling coefficient, the higher the static value of the transient magnetic induction.

Characterization of industrial low-density polyethylene: a thermal, dynamic mechanical, and rheological investigation

Thestudy of commercial low-density polyethylenes (LDPEs) has always focused on the effects of the molecular architecture of the polymer on its shear and extensional rheological properties due to their direct influence on manufacturability. However, the complex morphology of industrial-grade LDPEs also affects the crystallization kinetics and dynamic mechanical properties of the polymers, which are key to the processibility and applications. Therefore, a comprehensive investigation was conducted into the areas of crystallization kinetics, crystallinity, dynamic mechanical, and linear and non-linear shear rheological properties of two industrial-grade LDPEs to build a cohesive insight into the influence of morphology on these material properties. We further analyzed the steady-state and transient shear viscosity data obtained from the two LDPEs in comparison with constitutive model predictions using the hierarchical multi-mode molecular stress function (HMMSF) and found excellent agreement within experimental accuracy between predictions by the HMMSF model and shear stress as well as normal stress data of the LDPEs investigated.

Disintegration of low and normal strength concrete in shear localized bands and its constitutive modeling

The shear resistant mechanism along cracks of concrete changes as localized shear deformation progresses. The aggregate interlock mechanism shifts to the Coulomb friction mechanism. A disintegration model considering the transient shear transfer has been proposed. In this study, the applicability of this constitutive model to low and normal strength concrete was verified through experiments and post-peak analysis. As a conclusion, it is clarified that when this graveling formation progresses along the localized shear bands in structures, it is necessary to consider the transition of shear disintegration and the proposed model has fair consistency with the experimental results. Moreover, the average frictional coefficient of disintegrated cementitious composite is inversely idealized about 1.0 for concrete and about 0.4 for mortar. It is expected that the proposed model will increase the accuracy of analyzing the structural restoring force characteristics of reinforced concrete and its post-peak behaviors.

Extensional flow affecting shear viscosity: Experimental evidence and comparison to models

The effect of extensional flow on apparent shear viscosity has never previously been directly measured nor is it often considered. Here, for the first time, through using a novel flow configuration (two-phase shear response under extensional flow), we have directly measured the effect extensional flow has on the apparent shear viscosity of a viscoelastic polymer solution in a controlled and kinematically mixed manner. We show, via a control transient shear experiment, that the apparent shear viscosity of the solution under mixed deformation depends not only on the shear rate but also on the extension rate and their relative direction: shear thinning being enhanced by parallel and reduced by perpendicular extensional flow, respectively. A 62% reduction in apparent viscosity with parallel extension was seen in this work. We then test the ability of the commonly used Giesekus and Carreau–Yasuda (incorporating generalized shear rate) models to predict the effect of extension rate on apparent shear viscosity against our data. The Giesekus model was found to predict the correct qualitative behavior under both parallel and perpendicular extensional flow, and depending on the fitting parameters, also provided a loosely quantitative agreement. Conversely, the generalized shear rate description does not capture the qualitative behavior, with the most significant errors occurring for perpendicular extension (i.e., expansion) flows. This work emphasizes the rarely noted shortcomings of the latter approach when used for experimental analysis and engineering design when extensional flows are additionally present.

Computational analysis of the transient mixed convective flow of nanofluid in the plume regions

Computer microchips and many other electrical devices that use microfluidics use nanofluids as coolants. Nanofluids have a higher thermal conductivity due to the volumetric proportion of nanoparticles. Thus, as the nanofluids in engineering and industrial process have a significant role, the current study aims to focus on the transient mixed convective flow of nanofluid in the plume regions. The numerical solutions for the transient mixed convection flow in the form of amplitude and phase angle are performed reasonably. The desired nonlinear mathematical model is created by incorporating periodic behavior into conservation equations and appropriate boundary conditions. Using appropriate scaling variables, the dimensioned equations are transformed into dimensionless ones. Solutions for the values of Prandtl number Pr, Schmidt number Sc, thermophoretic parameter Nt, Brownian motion parameter Nb and mixed convection parameters and show that the coupling between the fluid and heat transfer can have dramatic effects on the transient shear stress heat and mass transfer. The buoyancy force acting on the heated boundary layer of nanofluid can also have a significant impact on transient skin friction, heat and mass transfer. The governing process is accelerating or depending upon the position of the sphere.

Recent developments on yield stress materials

<h2>Abstract</h2> Several gels, suspensions, emulsions and foams found both in nature and industrial processes and products are complex yield stress materials that exhibit a rich variety of mechanical responses, like elasticity and time-dependence, in addition to yielding. A rigorous definition and physical interpretation of the related material functions are challenging. In this talk we discuss how this complexity affects fundamental concepts and measurements of these materials. Our discussion covers different related topics, such as (i) the need for the introduction of a yield stress tensor, (ii) thixotropy modeling---including the choice of the microstructure destruction agent, (iii) rheological characterization with quasilinear large amplitude oscillatory shear, and (iv) transient and steady-state shear banding.

3D CFD simulation and analysis of transient flow in a water pipeline

Abstract A three-dimensional (3D) computational fluid dynamics (CFD) approach is developed to elaborate the water-hammer pipe flow and 3D detailed dynamic characteristics of a closing ball valve. The proposed CFD approach considers the water compressibility and the viscous sublayer, which are sometimes neglected in previous studies. Comparisons of the CFD results, the measured pressures and the one-dimensional results, demonstrate that the current 3D CFD approach better reproduces the experimental pressure oscillations while helping to visualize the associated physical processes and to further explore the 3D transient characteristics. The mean velocity distributions in the radial direction significantly change as the pipe transient progresses, which is closely associated with transient shear stress. Mean velocity variations at the valve during the closing process undergo three distinct stages: slight change, then drastic reduction, and finally slowing down. Head loss coefficient and discharge coefficient of the valve change as the valve closing time shortens.

A Thermodynamically Consistent, Microscopically-Based, Model of the Rheology of Aggregating Particles Suspensions.

In this work, we outline the development of a thermodynamically consistent microscopic model for a suspension of aggregating particles under arbitrary, inertia-less deformation. As a proof-of-concept, we show how the combination of a simplified population-balance-based description of the aggregating particle microstructure along with the use of the single-generator bracket description of nonequilibrium thermodynamics, which leads naturally to the formulation of the model equations. Notable elements of the model are a lognormal distribution for the aggregate size population, a population balance-based model of the aggregation and breakup processes and a conformation tensor-based viscoelastic description of the elastic network of the particle aggregates. The resulting example model is evaluated in steady and transient shear forces and elongational flows and shown to offer predictions that are consistent with observed rheological behavior of typical systems of aggregating particles. Additionally, an expression for the total entropy production is also provided that allows one to judge the thermodynamic consistency and to evaluate the importance of the various dissipative phenomena involved in given flow processes.

Enabling thermally enhanced vibration attenuation via biomimetic Zr–fumarate MOF-based shear thickening fluid

This work reported a biomimetic shear thickening fluid (STF) with thermally enhanced shear thickening effect for smart vibration attenuation system. It was developed by introducing Zr–fumarate metal-organic framework (MOF) crystals into a solvent mixture comprised of polyethylene glycol, polyacrylic acid and Ca2+, which endowed it with the cooperative effect of electrostatic and hydrophobic interactions. As the temperature raised from 25 to 35 °C, the STF containing 55 vol% MOF (STF-55) yielded a favorable shear thickening reinforcement with a notable viscosity growth of 1760-7953 Pa s. Besides, its storage modulus increased from 14 to 3036 Pa at 25–55 °C under a 0.1 Hz shear frequency, revealing a significant improvement in mechanical performance, as also demonstrated by transient shear rheological experiments. STF was incorporated into sandwich structures to improve the damping performance, with the natural frequency and damping ratio investigated at various ambient temperatures. Since the thermal enhanced viscosity could promote energy dissipation, the damping ratio of STF-55 filled sandwich structure obtained a substantial improvement from 0.85% to 1.93% at 25–55 °C. Thus, STF-55 based turbine blade and building damping pile were fabricated, which not only reduced the external vibration stimuli with average responsive accelerations of 7.3 and 0.8 m2s-1, but also presented attenuated levels of 6.9 and 0.6 m2s-1 at increasing temperatures, respectively. In conclusion, this work provided guiding approach for highly adaptive vibration attenuation at high-temperature environment.

Numerical investigation elucidating effects of microstructure on the transient thermomechanical phenomena during laser impact welding

Transient thermomechanical phenomena such as extreme plastic strains and temperature spikes that occur during laser impact welding are impractical to experimentally observe given the sub-microsecond duration of the joining process. Thus, computational models are necessary to study in-situ behavior along the weld interface. While researchers have utilized computational models for such investigations, this work elucidates the specific influence of microstructure-level modeling that captures the associated inhomogeneity/anisotropic effects at smaller scales. An aluminum 1100-H19 flyer and a stainless steel 304-O target foil are modeled using an Eulerian framework to simulate cases with and without microstructure consideration during laser impact welding of dissimilar metallic foils. When considering microstructure modeling, variations in flow stress reveal intermittently elevated temperatures along the weld interface due to concentrations of shock pressure at relatively small grains; however, they are not found to be a significant source of instability initiating or influencing the joint formation. Grain refinement and material hardening are suggested within a 10 μm-thick zone of the flyer near the weld interface, while severe plastic deformation in the target indicates possible martensitic phase transformation. Grain boundary sliding driven by variations in yield surfaces among individual grains gives rise to relatively higher collision velocity. Consequently, higher plastic strain rates along with greater amounts of plastic heat dissipation at the interface result in increased material jetting at higher temperatures. Alternating transient shear stresses are predicted in each model, though the inhomogeneous model predicts the brief appearance of a concentrated shear zone in the rebound region which is not seen in the homogeneous model. This work illuminates correlations between microstructure and transient phenomena during laser impact welding of dissimilar metallic foils, thus demonstrating a numerical modeling approach extensible to numerous other impact welding processes that complete within a very short time span.

Nonlinear rheology of entangled wormlike micellar solutions predicted by a micelle-slip-spring model

We examine linear and nonlinear shear and extensional rheological properties using a “micelle-slip-spring model” [T. Sato et al., J. Rheol. 64, 1045–1061 (2020)] that incorporates breakage and rejoining events into the slip-spring model originally developed by Likhtman [Macromolecules 38, 6128–6139 (2005)] for unbreakable polymers. We here employ the Fraenkel potential for main chain springs and slip-springs to address the effect of finite extensibility. Moreover, to improve extensional properties under a strong extensional flow, stress-induced micelle breakage (SIMB) is incorporated into the micelle-slip-spring model. Thus, this model is the first model that includes the entanglement constraint, Rouse modes, finite extensibility, breakage and rejoining events, and stress-induced micelle breakage. Computational expense currently limits the model to micellar solutions with moderate numbers of entanglements (≲7), but for such solutions, nearly quantitative agreement is attained for the start-up of the shearing flow. The model in the extensional flow cannot yet be tested owing to the lack of data for this entanglement level. The transient and steady shear properties predicted by the micelle-slip-spring model for a moderate shear rate region without significant chain stretch are fit well by the Giesekus model but not by the Phan–Thien/Tanner (PTT) model, which is consistent with the ability of the Giesekus model to match experimental shear data. The extensional viscosities obtained by the micelle-slip-spring model with SIMB show thickening followed by thinning, which is in qualitative agreement with experimental trends. Additionally, the extensional rheological properties of the micelle-slip-spring model with or without SIMB are poorly predicted by both the Giesekus and the PTT models using a single nonlinear parameter. Thus, future work should seek a constitutive model able to capture the behavior of the slip-spring model in shear and extensional flows and so provide an accurate, efficient model of micellar solution rheology.

Occurrence of sarcoptic mange in free-ranging vicuñas (Vicugna vicugna) of the Andean high plateau region of Argentina.

Free-ranging vicuñas (Vicugna vicugna) are handled in some areas of the Andean high plateau region following an ancestral practice known as chaku, which consists in their transient capture and shearing of their fiber for commercialization. In this study, 807 vicuñas captured during 12 chaku events that took place in 2019 in the province of Jujuy, Argentina, were examined for typical mange skin lesions. Twenty-eight of the examined vicuñas presented alopecia with erythema, exudation, hyperkeratosis, and/or bleeding scarred lesions, mostly in the chest, rear and front legs, and inguinal zone. Most of the cases (82%) appeared in Laguna Cucho at 4900 masl, where 23% of the animals presented these skin reactions. Microscopic evaluation of skin scrapings revealed the presence of a great number of 0.1- to 0.4-mm-long mites of different life cycle stages, morphologically compatible with the species Sarcoptes scabiei. This etiological agent was confirmed by PCR amplification and sequencing of a cox-1 species-specific segment. Histopathological examination of skin biopsies showed extensive infiltration of the dermis with lymphocytes, neutrophils and eosinophils, hyperplasia at different stages, epidermis degeneration, and hyperkeratosis. This is the first characterization of sarcoptic mange in free-ranging vicuñas by clinical examination, mite morphology, histopathological studies, and molecular confirmation in the region. Mange hampers the welfare of vicuñas and the economy of the local communities that organize chaku events since infested vicuñas cannot be sheared. Its long-term effects are unknown but it might affect the fitness and survival of this iconic South American camelid.

Stokes’ second problem and oscillatory Couette flow for a two-layer fluid: Analytical solutions

The unsteady motion of a two-layer fluid induced by oscillatory motion of a flat plate along its length is mathematically analyzed. Two cases are considered: (i) the two-layer fluid is bounded only by the oscillating plate (Stokes’ second problem), and (ii) the two-layer fluid is confined between two parallel plates, one of which oscillates while the other is held stationary (oscillatory Couette flow). In each of the Stokes and Couette cases, both cosine and sine oscillations of the plate are considered. It is assumed that the fluids are immiscible, and that the flat interface between the fluids remains flat for all times. Solutions to the initial-boundary value problems are obtained using the Laplace transform method.The results obtained for the velocity fields for the flows are new and complete. Steady periodic and transient velocity fields are explicitly presented. Transient and steady-state shear stresses at the boundaries of the flows are calculated; the existing literature lacks any such results. The results derived in this paper retrieve previously known results for corresponding single-layer flows. Furthermore, the results obtained are illustrated taking particular example of each of the Stokes’ problem and the Couette flow. With the help of the illustrations, some physical insights into the flows of the particular problems are gained. Again, the results obtained could also be applicable to a problem of heat conduction in a composite solid with sinusoidal temperature variation on the surface.

Power functional theory for many-body dynamics

The rich and diverse dynamics of particle-based systems ultimately originates from the coupling of their degrees of freedom via internal interactions. To arrive at a tractable approximation of such many-body problems, coarse-graining is often an essential step. Power functional theory provides a unique and microscopically sharp formulation of this concept. The approach is based on an exact one-body variational principle to describe the dynamics of both overdamped and inertial classical and quantum many-body systems. In equilibrium, density functional theory is recovered, and hence spatially inhomogeneous systems are described correctly. The dynamical theory operates on the level of time-dependent one-body correlation functions. Two- and higher-body correlation functions are accessible via the dynamical test particle limit and the nonequilibrium Ornstein-Zernike route. We describe the structure of this functional approach to many-body dynamics, including much background as well as applications to a broad range of dynamical situations, such as the van Hove function in liquids, flow in nonequilibrium steady states, motility-induced phase separation of active Brownian particles, lane formation in binary colloidal mixtures, and both steady and transient shear phenomena.

Long-Term Aging of Concentrated Aqueous Graphene Oxide Suspensions Seen by Rheology and Raman Spectroscopy.

Today, graphene oxide (GO) has gained well-deserved recognition, with its applications continuing to increase. Much of the processing of GO-based devices occurs in a dispersed form, which explains the commercialization of GO suspensions. Aging of these suspensions can, however, affect the shelf life and thus their application potential. Aging of GO preparations is often acknowledged, but no longer-term systematic study has been reported on the alteration of GO suspensions. This paper investigates high-concentration (10 mg/mL) aqueous GO suspensions over a 2-year time scale. In addition to steady shear tests, the dynamic behavior of the suspensions was studied in more detail by transient shear and frequency sweep measurements. Both the viscosity and the dynamic moduli increased with age, particularly within the first year. The results of the complementary Raman spectroscopic studies indicate that the change in the rheological behavior with aging results from a slow oxidation process occurring in the highly acidic aqueous medium during the relatively long-term storage. The (over)oxidized layers peel off spontaneously or are removed by high shear stress, resulting in increased viscosity, as it was corroborated by XRD and XPS.

Rheological analysis of bio-ink for 3D bio-printing processes

3D bio-printing is an emerging technology to fabricate tissue scaffold in-vitro through the controlled allocation of biomaterial and cells, which can mimic the in-vivo counterpart of living tissue. Live cells are often encapsulated into the biomaterials (i.e., bio-ink) and extruded by controlling the printing parameters. The functionality of the bioink depends upon three factors: (a) printability, (b) shape fidelity, and (c) bio-compatibility. Increasing viscosity will improve the printability and the shape fidelity but require higher applied extrusion pressure, which is detrimental to the living cell dwelling in the bio-ink, which is often ignored in the bio-ink optimization process. This paper demonstrates a roadmap to develop and optimize bio-inks, ensuring printability, shape fidelity, and cell survivability. The pressure exerted on the bio-ink during extrusion processes is measured analytically, and the information is incorporated in the bio-ink's rheology design. Cell-laden filaments are fabricated with multiple cell lines, i.e., Human Embryonic Kidney (HEK 293), BxPC3, and prostate cancer cells which are analyzed for cell viability. The cross-sectional live-dead assay of the extruded filament demonstrates a spatial pattern for HEK 293 cell viability, which correlates with our analytical finding of the shear stress at the nozzle tip. All three cell lines were able to sustain a transient shear stress of 3.7 kPa and demonstrate 90% viability with our designed bio-ink after 15 days of incubation. Simultaneously, the shape fidelity and printability matrices show its suitability for 3D bio-printing process.

Characterization of visco-hyperelastic behavior of open cell polyurethane foam through transient shear testing

Soft materials find ever-growing use in load-bearing applications, and hence, there is an imminent need for accurate testing and modeling of their mechanical properties. Nonlinearities and rate-dependence are inherent in the mechanical response of such materials, thanks to their multiphasic flexible constituents. Fragility of soft materials and rapid changes in their constituents depending on the environment add further challenges in mechanical characterization. This study introduces an efficient methodology to measure nonlinear viscoelastic properties of soft materials from transient shear response and validates the methodology experimentally on flexible polyurethane foams. Direct estimation of friction forces due to the Poynting effect and independent uniaxial compression tests of the same foam are also documented, validating the characterization framework. Both methods deliver comparable results with the transient-shear-based framework. Simple sample preparation and installation further complements the reliable and quick estimation capability, and thus offers a suitable characterization methodology for fragile and time-sensitive samples such as biological tissues. While validating the proposed framework on foams, fast relaxations and sensitivity to peak strains and strain rates are observed. Buckling and failure of the foam in the vicinity of the inertial plate could be possible explanations of those observations. Besides estimating the visco-hyperelastic properties of the foams, the tester dissipation stemming from material and frictional damping is also estimated in the framework. Increases in frictional dissipation due to compromised lubrication in guide rails over a period of three days are observed to shorten transients. Proper lubrication and control of friction before each test suppresses stochastic dry friction and improves repeatability and accuracy of the material characterization methodology.

A new slit‐radial die for simultaneously measuring steady state shear viscosity and first normal stress difference of viscoelastic liquids via capillary rheometry

AbstractA new slit‐radial die capable of simultaneously obtaining steady state shear viscosity and the average first normal stress difference coefficient via capillary rheometry has been developed. The steady state shear viscosity and average first normal stress difference coefficient are calculated in the slit part and radial part of the die, respectively. The steady state shear viscosity from the slit part of the slit‐radial die is compared to shear viscosities obtained from a capillary die and also the magnitude of the complex viscosity obtained from oscillatory shear experiment. The average value of first normal stress difference coefficient which is calculated in the radial part of the slit‐radial die is compared to first normal stress difference coefficient obtained from transient shear experiment in a cone‐plate geometry and the molecular stress function model predictions. The effect of variation of power law fitting parameters (consistency index, k and power law index, n) on average value of the first normal stress difference coefficient obtained from the radial part of the slit‐radial die is discussed. As this die has the shape of the city map of Karlsruhe it is named as Karlsruhe die.