Continuous Shear Research Articles

Numerical simulation of the droplet formation involving fluids with high viscosity ratio by lattice Boltzmann method

A multiple-relaxation-time color gradient lattice Boltzmann model is established for simulating the flow mechanism of viscous fluids or fluids with high viscosity ratios in the microchannel. The regularized method is incorporated in this MRT framework to deal with the high viscosity ratio problems involving practical inlet–outlet boundaries. By taking several static and dynamic cases, we prove that this model could accurately describe interfacial tension, wettability, and flow problems in two-phase flows with a low spurious velocity at the range of viscosity ratio up to O(103). Using this model, we successfully simulate the droplet formation process of fluids with a high viscosity ratio in the common T-junction channel. The results are in good agreement with the experiments in the literature. We further investigate the effect of high viscosity ratios on the dispersion process, revealing that the substantial increase in terms of the viscosity ratio of fluids leads to the enhancement of continuous phase viscous shear and dispersed phase inertia effect, which would bring the deviation of the operating range from mostly reported flow systems.

Investigation of tool damage in shear cutting of ultra-high strength sheet steels

Proportions of high- and ultra-high strength steels are constantly increasing in modern car bodies. In the press shop there are uncertainties concerning the application of steels with strength higher than 1000MPa particularly concerning shear cutting processes. To support the steel user regarding a tool material and coating and the wear behavior, long-term shear cutting test had been carried out. The effects of various shear cutting conditions on tool damage were investigated by continuous shear cutting test with an amount of cutting cuts up to 100,000 times. Tested sheet materials were 780, 1’180 and 1’470MPa grade steels. The changed cutting conditions were sheet steel strength, tool material, cutting clearance, and rake angle. Measurements by laser and confocal microscopes were carried out in order to reveal tool damage mechanisms. The features of tool damage were classified as wear, chipping, and plastic deformation. The amount of plastic deformation rises with the increase of sheet steel strength. Not only plastic deformation but also chipping in the tested tool was observed in the cutting test of 1180MPa sheet steel by standard tool steel (DIN 1.2379) after 40’000 cuts. Large plastic deformation in the tested tool was observed in a cutting test of 1470MPa sheet steel by high-speed steel (DIN 1.3343) after 100’000 cuts although no chipping was detected. Under a rake angle of 5°, serious chipping and tool wear were observed especially near the final sheet-tool contact position. Regarding clearance, the amount of plastic tool deformation increased with the decrease of the clearance. This effect of the clearance can be explained by vertical force and by sheet rotation during cutting.

Assessment of a Discogenic Pain Animal Model Induced by Applying Continuous Shear Force to Intervertebral Discs

BACKGROUND: Chronic discogenic pain includes degeneration-driven changes under the mechanical macroenvironment of an internal disc, which leads to the progressive changes of biochemical microenvironment that induce abnormal ingrowth of the nociceptor. The propriety of the animal model reflecting the pathologic natural history has not been assessed. OBJECTIVES: This study investigated the biochemical evidence of chronic discogenic pain by employing a discogenic pain animal model induced by shear force. STUDY DESIGN: Animal study utilizing rats in vivo model of a shear force device. METHODS: Fifteen rats were divided into 3 groups (n = 5/group) according to the period for which sustained dorsoventral shear force was applied (1 week or 2 weeks); the control group received the spinous attachment unit, without a spring. Pain data were collected using von Frey hairs on the hind paws. Growth factor and cytokine abundance was analyzed in the dorsal root ganglion (DRG) and plasma. RESULTS: After the shear force devices were installed, the significant variables were found to markedly increase in the DRG tissues of the 2-week group; however, they were not altered in the 1-week group. Specifically, interleukin (IL)-6, neurogrowth factor (NGF), transforming growth factor (TGF)-alpha, platelet-derived growth factor (PDGF)-beta, and vascular endothelial growth factor (VEGF) were increased. Meanwhile, the plasma levels of tumor necrosis factor-alpha, IL-1beta, IL-5, IL-6, IL-12, and NGF were increased in the 1-week group; whereas, TGF-alpha, PDGF-beta, and VEGF were increased in the 2-week group. LIMITATIONS: The limitations include the general limitations of quadrupedal animals, the poor precision and flexural deformation of shear force devices, inaccuracies regarding the evaluation of histological denaturation, and short intervention and observational periods. CONCLUSIONS: This animal model effectively generated biochemical responses to shear loading with evidence of neurological changes induced without direct macrodamage to the outer annulus fibrosus. Chemical internals were induced by mechanical externals among the contributing factors of chronic discogenic pain. KEY WORDS: Discogenic pain, dorsal root ganglion, intervertebral discs, low back pain, shear force, interleukin, growth factor, animal model

Role of dislocation climb on twin boundary and antiphase boundary formations in inverse-spinel MnAl2O4

The defects, e.g., stacking faults (SFs), antiphase boundaries (APBs), and twin, have been considered the critical components commonly introduced during the synthesis process of spinel oxides. In this study, employing advanced transmission electron microscopy, the formation mechanisms of twin and APBs in MnAl2O4 spinel oxide were clarified. Atomic resolution scanning transmission electron microscopy image and image simulation clarify that MnAl2O4 holds the inverse-spinel-typed structure. Detailed analysis of the twin structure reveals that the asymmetric twin structure in MnAl2O4 forms through an (Mn, Al)-containing plane missing by dislocation climb-up and then continuous shearing on {111} plane. APB forms by dislocation climb-down on an (Mn, Al)-containing {111} plane. The detailed lattice distortion induced by dislocation climb-down was analyzed by geometric phase analysis. The burgers vector for APB formation is identified as a/61̅1̅1+a/411̅0. Frank dislocation of a/61̅1̅1 climb-down and the lattice strain from introducing the extra plane brings a displacement of a/411̅0, which results in terrace-ledge-like morphology of APBs. This study provides a detailed understanding of twin and APB formation mechanisms in inverse-spinel-typed MnAl2O4.

Fabrication of polyphenylene sulfide composites with integrated mechanical and tribological properties by synchronically adding irradiation-treated PTFE powders and short carbon fibers

In this work, irradiation-treated polytetrafluoroethylene (i-PTFE) powders and short carbon fibers (SCFs) were synchronically incorporated to prepare polyphenylene sulfide (PPS)-based composites with integrated tribological and mechanical properties. The results revealed that the combined addition of i-PTFE powders and SCFs favored the formation of transfer film on the surface of friction pair and lubricating film on the surface of sample block, which was crucial to improving the tribological properties. In addition, the thermal conductivity of PPS-based composites was greatly enhanced with the addition of SCFs, which was advantageous to the dissipation of friction heat at the sliding interface. The mechanical properties, including tensile and flexural properties as well as surface hardness of PPS/i-PTFE/SCF composites were greatly enhanced with ≥ 10 wt% SCFs when compared with those of pure PPS and PPS/i-PTFE blends, which was beneficial to withstand the continuous shearing action of friction pair. As a result, the average friction coefficient and specific wear rate of PPS/i-PTFE 24 wt%/SCFs 20 wt% composites reached 0.160 and 3.63 × 10−6 mm3/Nm, which were 71.4% and 99.0% lower than those of pure PPS. This work demonstrated that thermoplastic engineering composites with integrated mechanical and tribological properties can be prepared by synchronically adding i-PTFE and SCFs which show promising applications in the fields of automotive, aviation and aeronautics, etc.

Mesoscopic evolution and kinetic properties of dense granular flow crystallization under continuous shear induction

The influence of spatial structure on the kinetic response of discrete soft matter is critical. The exploration is not limited to structural evolution, jamming point, phase transition, etc. However, the mesoscopic response under continuous loading has always been difficult to make progress in experiments. In this study, we explored the mesoscopic evolution and properties of the ordered structure in dense granular flow under continuous shear by experiments and simulations. It shows that the crystal structure of the particles develops simultaneously inward from the boundary of the shearing cell. Two morphological clusters formed one after another within a 2D cylindrical layer parallel to the boundary. At the single-particle level, continuous strain is found to make the crystallization process within the cylindrical layers an evolution of chain-like polycrystalline to monocrystal structures. Compared to oscillatory shear, splicing or fusion is the way to reach the final state from the transition state under continuous shear rather than epitaxial growth. Due to continuous shear, the symmetry of the crystal switches between hexagonal close-packed (HCP) and face-centered cubic (FCC) and is dynamically balanced in the flow. We also describe the switching path. The results show that HCP in flow is more favored by the environment than FCC.

Acute and reversible modulation of kidney proximal tubule endocytic capacity by fluid shear stress

The proximal tubule (PT) of the kidney is comprised of cells that are uniquely specialized for efficient apical uptake of albumin and other proteins that escape the glomerular filtration barrier. These proteins bind to the multiligand receptors megalin and cubilin and are internalized via clathrin-dependent endocytosis into apical early endosomes that rapidly mature into larger apical vacuoles (AVs). Dissociated ligands are delivered from AVs to lysosomes for degradation, while receptors are collected into dense apical tubules for recycling to the cell surface. When cells are grown under continuous fluid shear stress (FSS), the endocytic uptake is approximately 9-fold greater than static cells. Additionally, cells cultured in this manner rapidly and reversibly adjust their endocytic capacity in response to changes in FSS. We hypothesize flow-dependent modulation of endocytic capacity enables PT cells in vivo to preserve uptake efficiency in response to changes in glomerular filtration. We are combining biochemical, imaging, and mathematical modeling approaches to determine the mechanism(s) by which cells chronically and acutely modulate endocytic uptake. Increased levels of megalin transcripts (~2x) and protein (~4x) is insufficient to account for the large increase in endocytic uptake observed in cells cultured under FSS vs static conditions. We used cell surface biotinylation experiments to compare the fraction of megalin at the surface, the fraction endocytosed, and the half-life of surface-tagged megalin under FSS and static conditions. These data were used to adapt a kinetic model that describes kinetics of megalin biosynthesis, trafficking, and degradation in cells. Overall, the cells grown under FSS have a greater endocytic rate and recycling rate compared with static grown cells. By contrast, megalin degradation is faster than recycling in static-grown cells. Colocalization of megalin with known markers of apical compartments will enable us to extend our model to determine whether changes in endosomal maturation rates contribute to these differences. Additionally, cells cultured under continuous FSS rapidly and reversibly adjust their endocytic capacity in response to changes in shear stress. We hypothesize flow-dependent modulation of endocytic capacity enables PT cells in vivo to preserve uptake efficiency in response to changes in glomerular filtration. We are currently adapting our model to determine how acute changes in shear stress trigger alterations in endocytic uptake. National Institute of Health: 5T32GM133353-03, R01 DK118726, R01 DK125049 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Existence of Steady Solutions for a Model for Micropolar Electrorheological Fluid Flows with Not Globally log-Hölder Continuous Shear Exponent

In this paper, we study the existence of weak solutions to a steady system that describes the motion of a micropolar electrorheological fluid. The constitutive relations for the stress tensors belong to the class of generalized Newtonian fluids. The analysis of this particular problem leads naturally to weighted variable exponent Sobolev spaces. We establish the existence of solutions for a material function {hat{p}} that is log -Hölder continuous and an electric field textbf{E} for that vert textbf{E}vert ^2 is bounded and smooth. Note that these conditions do not imply that the variable shear exponent p={hat{p}}circ vert textbf{E}vert ^2 is globally log -Hölder continuous.

Analogy between streamers in sinking spheroids, gyrotactic plumes and chemotactic collapse

In a dilute suspension where sinking spheroids or motile gyrotactic micro-organisms are modelled as orientable and negatively buoyant particles, we have found analytical solutions to their steady distributions under any arbitrary continuous vertical shear flow. The two-way coupling between their distribution and the vertical flow is nonlinear, enabling the uniform base state to bifurcate into a structure reminiscent of the streamers in settling spheroid suspensions and gyrotactic plumes. This bifurcation depends on a single parameter that is proportional to the average number of particles on a horizontal cross-section. In a three-dimensional axisymmetric system, the plume structure blows up when the parameter is above a threshold. We discuss how this singularity is analogous to the chemotactic collapse of a Keller–Segel model, and the significance that this analogy entails.

Shear-Mediated Platelet Microparticles Demonstrate Phenotypic Heterogeneity as to Morphology, Receptor Distribution, and Hemostatic Function.

Implantable Cardiovascular Therapeutic Devices (CTD), while lifesaving, impart supraphysiologic shear stress to platelets, resulting in thrombotic and bleeding coagulopathy. We previously demonstrated that shear-mediated platelet dysfunction is associated with downregulation of platelet GPIb-IX-V and αIIbβ3 receptors via generation of Platelet-Derived MicroParticles (PDMPs). Here, we test the hypothesis that sheared PDMPs manifest phenotypical heterogeneity of morphology and receptor surface expression and modulate platelet hemostatic function. Human gel-filtered platelets were exposed to continuous shear stress. Alterations of platelet morphology were visualized using transmission electron microscopy. Surface expression of platelet receptors and PDMP generation were quantified by flow cytometry. Thrombin generation was quantified spectrophotometrically, and platelet aggregation was measured by optical aggregometry. Shear stress promotes notable alterations in platelet morphology and ejection of distinctive types of PDMPs. Shear-mediated microvesiculation is associated with the remodeling of platelet receptors, with PDMPs expressing significantly higher levels of adhesion receptors (αIIbβ3, GPIX, PECAM-1, P-selectin, and PSGL-1) and agonist receptors (P2Y12 and PAR1). Sheared PDMPs promote thrombin generation and inhibit platelet aggregation induced by collagen and ADP. Sheared PDMPs demonstrate phenotypic heterogeneity as to morphology and defined patterns of surface receptors and impose a bidirectional effect on platelet hemostatic function. PDMP heterogeneity suggests that a range of mechanisms are operative in the microvesiculation process, contributing to CTD coagulopathy and posing opportunities for therapeutic manipulation.

Challenging the assumption of uniformity in patellar tendon structure: Regional patellar tendon morphology and mechanical properties in vivo.

Patellar tendons are assumed to be uniform in morphology and mechanical properties despite a higher prevalence of tendinopathies observed in the medial region. The purpose of this study was to compare the thickness, length, viscosity, and shear modulus of the medial, central, and lateral regions of healthy patellar tendons of young males and females in vivo. B-mode ultrasound and continuous shear wave elastography were performed on 35 patellar tendons (17 females, 18 males) over three regions of interest. A linear mixed-effects model (α = 0.05) was used to determine differences between the three regions and sexes followed by pairwise comparisons for significant findings. The lateral region (mean [95% confidence interval] = 0.34 [0.31-0.37] cm) was thinner compared with the medial (0.41 [0.39-0.44] cm, p < 0.001), and central (0.41 [0.39-0.44] cm, p < 0.001) regions regardless of sex. Viscosity was lower in the lateral (19.8 [16.9-22.7] Pa-s) versus medial region (27.4 [24.7-30.2] Pa-s, p = 0.001). Length had a region-by-sex interaction (p = 0.003) characterized by a longer lateral (4.83 [4.54-5.13] cm) versus medial (4.42 [4.12-4.72] cm) region in males (p < 0.001), but not females (p = 0.992). Shear modulus was uniform between regions and sexes. The thinner, and less viscous lateral patellar tendon may reflect the lower load the tendon experiences explaining the differences in regional prevalence of developing tendon pathology. Statement of Clinical Significance: Healthy patellar tendons are not uniform in morphology or mechanical properties. Considering regional tendon properties may help guide targeted interventions for patellar tendon pathologies.

Shear strengthening of continuous RC T-beams with deep embedded CFRP and steel bars: A numerical study

This paper presents a non-linear finite element parametric study of continuous RC T-beams shear retrofitted with deep embedded (DE) carbon fibre reinforced polymer (CFRP) bars and steel bars. Two-dimensional nonlinear finite element (NLFE) models for these shear-retrofitted beams have been developed and validated with the published literature based on the ultimate shear strength, load versus displacement behaviour, failure mode and strain developed in the longitudinal steel at mid-span. NLFE models of five RC T-beams are developed, out of which one model is for the un-strengthened beam, two are for the shear retrofitted beams with vertical DE bars and the leftover two are for the shear retrofitted with inclined 45° DE bars. Parametric investigations have been conducted to evaluate the impacts of shear span to depth ratio (a/d), compressive strength of concrete, effective beam depth and DE bar reinforcement to the existing shear links ratio on the shear strength, load versus deflection behaviour and strain developed in the shear links of these continuous beams. It is found that the above considered parameters of the continuous RC-T beams influence the shear capacity, load–displacement behaviour and strain in the shear link significantly. Moreover, the present work will provide sufficient knowledge to the designers for designing the shear retrofitted RC beams with DE bars.

Dislocation behavior in Cu single crystal joints under the ultrasonically excited high-strain-rate deformation

• The interfacial evolution for ultrasonically welded joints was used to clarify the coupling effects of ultrasonic excitation and high-strain-rate deformation. • Transmission Kikuchi diffraction and transmission electron microscopy were used to analyze grain orientation and deformed microstructures simultaneously. • Ultrasonic excitation dramatically weakened the constraint of high-strain-rate and characteristic orientations on dislocation motion. • The first-principle calculation and applied strain-rate analysis were conducted to discuss the preferred deformation mechanism to accommodate the imposed plastic strain. The coupling effects of ultrasonic excitation and high-strain-rate deformation are the core factors for weld formation during ultrasonic welding. However, interfacial deformation behavior still shrouds in uncertainty because of the contradictory features between mutual dislocation retardation caused by severely frictional deformation and ultrasonic-accelerated dislocation motion. [101] and [111]-oriented Cu single crystals which tended to form geometrically necessary boundaries (GNBs) were selected as the welding substrates to trace the uniquely acoustoplastic effects in the interfacial region under the ultrasonically excited high-strain-rate deformation. It was indicated that for a low energy input, micro-welds localized at the specific interface region, and equiaxed dislocation cells substituting for GNBs dominated in the initial single crystal rotation region. As the welding energy increased, continuous shear deformation drove the dynamic recrystallization region covered by equiaxed grains to spread progressively. Limited discrete dislocations inside the recrystallized grains and nascent dislocation cells at the grain boundaries were observed in [101] and [111] joints simultaneously, suggesting that the ultrasonic excitation promoted motion of intragranular dislocation and pile-up along the sub-grain boundaries. The interfacial morphology before and after expansion of recrystallization region all exhibited the weakening of orientation constraint on dislocation motion, which was also confirmed by the similar micro-hardness in joint interface. The first-principle calculation and applied strain-rate analysis further revealed that ultrasonic excitation enhanced dislocation slipping, and enabled dislocation motion to accommodate severe plastic deformation at a high-strain-rate.

Role of Inherited Tectonic Structures on Gravity-Induced Slope Deformations: Inference from Numerical Modeling on the Luco dei Marsi DSGSD (Central Apennines)

A pre-existing and inherited geostructural setting plays a fundamental role in preparing and developing large-scale slope deformational processes. These structures affect the kinematics of the process, the geometrical characteristics, and the geomorphological evolution. In the Apennine Belt, several deep-seated gravitational slope deformations (DSGSDs) that have evolved under a clear structural control have been recognized during the last decades, but none with a continuous and well-defined basal shear zone (BSZ). The structurally-controlled DSGSD of Luco dei Marsi represents the first case of a DSGSD in the Apennine Belt with a well-defined BSZ. Starting from a detailed study of the process and the reconstruction of a morpho-evolutionary model of the slope, a series of numerical modelings were performed for the study of the DSGSD. The analyses allowed us to reconstruct: (i) the mechanism of the process, (ii) the rheological behavior of the rock mass, and (iii) the main predisposing factors of the gravitational deformation. Numerical modeling has demonstrated the significant role played by the inherited structures on the DSGSD and, in particular, the importance of an intensely jointed stratigraphic level in the development of the BSZ.

Shear-induced phenotypic transformation of microglia in vitro

The brain cells are affected by continuous fluid shear stress that is driven by varying hydrostatic and osmotic pressure conditions, depending on the brain’s pathophysiological conditions. Although all brain cells are sensitive to the subtle changes in various physicochemical factors in the microenvironment, microglia, the resident brain immune cells, exhibit the most significant morphodynamic transformation. However, little is known about the phenotypic alterations in microglia in response to changes in fluid shear stress. In this study, we established a flow-controlled microenvironment to investigate the effects of shear flow on microglial phenotypes, including morphology, motility, and activation states. We observed two distinct morphologies of microglia in a static condition: bipolar cells that oscillate along their long axis and unipolar cells that migrate persistently. When exposed to flow, a significant fraction of bipolar cells showed unstable oscillation with an increased amplitude of oscillation and a decreased frequency, which consequently led to the phenotypic transformation of oscillating cells into migrating cells. Furthermore, we observed that the level of proinflammatory genes increased in response to shear stress, although there were no significant changes in the level of antiinflammatory genes. Our findings suggest that an interstitial fluid-level stimulus can cause a dramatic phenotypic shift in microglia toward proinflammatory states, shedding light on the pathological outbreaks of severe brain diseases. Given that the fluidic environment in the brain can be locally disrupted in pathological circumstances, the mechanical stimulus by fluid flow should also be considered a crucial element in regulating the immune activities of the microglia in brain diseases.

Experiment and particle flow simulation of unloading induced shearing properties for jointed sandstone materials

Shear tests on sandstone containing non-connected joints under the unloading normal stress but fixed shear stress conditions were conducted with various initial normal stress and unloading rate. During the unloading process, continuous shear dilation could be observed. For initial normal stress = 5–20 MPa, the sliding initiation normal displacement decreased by 17.14–66.32 % but the sliding initiation shear displacement increased by 21.91–98.19 %. The sliding initiation normal stress declined by 7.18–15.57 % for unloading rate = 0.002–0.01 MPa/s but increased by a factor of 3.18–3.53 with the initial normal stress. Shear sliding of the jointed samples was more prone to occur at a smaller initial normal stress with a larger unloading rate. From the numerical simulation results via PFC2D, during the unloading process, cracking was first initiated from central part of the rock bridge and propagated gradually to coalesce with cracks developed from the joint tips. The penetrating fracture surfaces led to shear sliding of the jointed samples, and shear wear occurred on the fractures as shear displacement continued increasing. For unloading rate = 0.002–20 MPa/s, quantity of cracks corresponding to shear displacement of 1.2 mm decreased by 12.18–36.34 %. Cracking degree was more serious for the samples at a low unloading rate due to progressively developed cracks near the main failure planes before shear sliding and more accumulated cracks in the shearing wear stage for fractures under a larger normal stress.

Understanding the Early Stage of Planet Formation: Design and Demonstration of the Space Experimental Apparatus

Planet formation begins with the collision and growth of dust in protoplanetary disks. Concerning the basic cognition of the early stage of planet formation, a long-standing weakness of the research is a comprehensive physical model describing the collisional evolution of dust particles. Microgravity experiments providing original data are crucial in developing related theories. In this work, we propose an experimental scheme for observing the collisional growth of dust analogues under a unidirectional and continuous shearing process, aiming at a future implementation in space experiments. The experimental process is simulated using the discrete element method, and the atlas of the design parameter versus the evolutionary path is depicted. We notice fractal structures and growth stalling as remarkable outcomes in the process of collisional growth, which is analogous to the evolutionary mechanism in the ancient protoplanetary disks. Based on these phenomena, we determine the sensitive design parameters, i.e., the shear velocity and the filling factor, which serve as the recommended parameters in future space experiments. The validation using numerical experiments shows that the experimental scheme with proper design parameters is feasible, which promises to generate constructive data that will facilitate the development of planet formation theory.

A novel higher-order refined zigzag theory for static bending analysis in sandwich composite beam

Sandwich composite beams are widely used in variety fields. A typical sandwich composite beam includes a soft core covered by two stiff face layers. For such beam structures, large stiffness difference between two adjacent layers can result in shear deformations and zigzag displacement phenomenon. In this research, a novel higher-order refined zigzag theory (HRZT) is presented for solving the static bending problems of a sandwich composite beam with a soft core. The HRZT is derived based on the refined zigzag theory (RZT) by adding the higher-order zigzag terms. Unlike RZT, the kinematics assumption of HRZT can obtain a continuous shear stress distribution across the thickness. The governing equations of HRZT are derived by variational principle and the general solutions of which are derived in exact forms. The HRZT, RZT and FEM with commercial software are used to solve the static bending responses of sandwich composite beams with cantilevered and simply-supported boundary conditions. By comparing the FEM results, both the displacements and shear stresses calculated by HRZT are verified with high accuracy. In the present study, it is shown that HRZT is able to preserve the advantages of the RZT on the modelling of the zigzag displacement, but also improves the shear stress distributions that are continuous across the interface between two layers.

On the structure of the turbulent/non-turbulent interface in a fully developed spatially evolving axisymmetric wake

In this work, we numerically study the structure of the turbulent/nonturbulent (T/NT) interface in a fully developed spatially evolving axisymmetric wake by means of direct numerical simulations. There is a continuous and contorted pure shear layer (PSL) adjacent to the outer edge of the T/NT interface. The local thickness of the PSL δPSL exhibits a wide range of scales (from the Kolmogorov scale to the Taylor microscale) and the conditional mean thickness 〈δPSL〉I/ηc≈6 with ηc being the centerline Kolmogorov scale is the same as the viscous superlayer. In the viscous superlayer, the pure shear motions without rotation are overwhelmingly dominant. It is also demonstrated that the physics of the turbulent sublayer is closely related to the PSL with a large thickness. Another significant finding is that the time averaged area of the rotational region 〈AR〉, and the pure shear region 〈AS〉 at different streamwise locations scale with the square of the wake-width bU2. This study opens an avenue for a better understanding of the structures of the T/NT interface.

Self-healing master curves of bituminous binders: a non-linear viscoelastic continuum damage framework

In this paper the viscoelastic continuum damage theory was used to investigate the damage and self-healing potential of bituminous binders, considering the effects of rest temperature, thixotropy, and non-linearity. Experimental testing was carried out by using a procedure in which continuous oscillatory shear loading was imparted to the specimens with the inclusion of a single rest period under multiple temperature conditions. Quantification of self-healing included the determination of material integrity gained and damage parameter recovered after the rest period. Such parameters were calculated by excluding time-dependent and non-linear biasing effects, which were directly evaluated by means of a distinct set of experiments. Results were modelled by using the so-called self-healing master curves, constructed by applying the linear viscoelastic time-temperature shift factors. These self-healing master curves are intended to be used as straightforward tools for the prediction of the self-healing response of neat and polymer modified binders in various time-temperature combinations.