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This manuscript presents the comprehensive study of thickness stretching effects on the free vibration, static stability and bending of multilayer functionally graded (FG) carbon nanotubes reinforced composite (CNTRC) nanoplates. The nanoscale and microstructure influences are considered through a modified nonlocal strain gradient continuum model. Based on power-law functions, four different patterns of CNTs distribution are considered in this analysis, a uniform distribution UD, FG-V CNTRC, FG-X CNTRC, and FG-O CNTRC. A 3D kinematic shear deformation theory is proposed to include the stretching influence, which is neglected in classical theories. Hamilton’s principle is applied to derive the governing equations of motion and associated boundary conditions. Analytical solutions are developed based on Galerkin method to solve the governing equilibrium equations based on the generalized higher-order shear deformation theory and the nonlocal strain gradient theory and get the static bending, buckling loads, and natural frequencies of nanoplates. Verification with previous works is presented. A detailed parametric analysis is carried out to highlight the impact of thickness stretching, length scale parameter (nonlocal), material scale parameter (gradient), CNTs distribution pattern, geometry of the plate, various boundary conditions and the total number of layers on the stresses, deformation, critical buckling loads and vibration frequencies. Many new results are also reported in the current study, which will serve as a benchmark for future research.

This paper focused on studying the transeverse deflection behavior of three functionally graded microbeam models: material, porous material, and functionally graded single-walled carbon nanotube-reinforced composite (FG-SWCNTRC) microb beam. To calculate micro size effects of the non-classical beam model, the modified couple stress theory (MCST) uses just length material scale parameters. A numerical solution to the static deflection equation is the Lagrange multiplier method. The characteristics studied included length, material parameter ratio, volume fraction of material, porosity and carbon nanotube, SWCNT distribution types, boundary conditions, and aspect ratio (length/thickness). The static behavior of FG-micro beams demonstrates that the theory of modified couple stress (MCST) produces more accurate results than classical beams. This is especially true if the beam thickness is close to the length scale parameter. As the CNT volume fraction grows and the porosity volume fraction falls, the microbeam FG structure deflects less.

A multitude gratings design consists of gratings with different pitches ranging from the micrometre down to sub 40 nm scale combined with sub 10 nm step heights modulating the surface morphology for length scale measurements is proposed. The surface morphology modulation was performed using electron beam lithography incorporating a standard semiconductor processing technology. The critical dimension, edge roughness, step heights and line morphology in dependence on the grating pitch is studied.

The turbulent energy dissipation rate is an important parameter that determines the transfer rates of mass, heat and momentum in chemical engineering industry. Especially in a multiphase reactor, the local instantaneous turbulent dissipation rate affects the breakage and coalescence of bubbles or droplets. To directly determine the local turbulent dissipation rate, fluctuating velocity gradients have to be measured down to the Kolmogorov length scale. This paper compares the advantages and disadvantages of three different methods, namely, correlation method, optical flow method and hybrid method, in the evaluation of velocity fields, which are subsequently used to calculate the turbulent dissipation rate. An instantaneous flow field of homogeneous isotropic turbulence from DNS results is used as a benchmark. The velocity field and turbulent dissipation rate field obtained by these three methods are compared to the DNS results. It is shown that the hybrid method performs better in both velocity field evaluation and local turbulent dissipation rate estimation compared to the other two methods. This is because the hybrid method combines the advantages of the correlation method in achieving a stable averaged velocity field and the optical flow method in achieving pixel-level resolution measurement of the flow field.

Partial substitution of hydrocarbon fuel with hydrogen can effectively improve small-scale combustion system stability and performance, potentially opening the way for novel compact power generation and/or propulsion systems in the future. In this study, the effects of hydrogen enhancement between 0% and 40% hydrogen volumetric fractions in methane fuel were experimentally observed in a mesoscale burner array subjected to external acoustic perturbations. The mesoscale burner array utilizes an array of swirl-stabilized burner elements and their interactions with neighboring elements to improve the overall flame stability and simultaneously reduces the combustor length scale. OH∗ chemiluminescence and OH planar laser-induced fluorescence (OH-PLIF) were used to image various hydrogen-enriched flames at an equivalence ratio of 0.7, subjected to transverse acoustic perturbations at 320 Hz. Two acoustic modes were imposed by controlling the phase difference between two speakers perturbing the flow. OH∗ chemiluminescence images exhibited flame length scale reduction, leading to a denser flame array. Also, flame arrays with higher hydrogen enrichment were found to be more robust against transverse acoustic perturbations, demonstrated by reduced fluctuations in the global heat release rate. OH-PLIF images showed that flames with higher hydrogen enrichment initiated V- to M-shaped flame shape transition even under fuel lean conditions, thereby improving the combustion stability. OH-PLIF images were also used for flame stability analysis through spectral proper orthogonal decomposition (SPOD). The SPOD analysis showed hydrogen enrichment diminished flame fluctuation structures under fuel lean operation.

We investigate the nonlinear bending behavior of nanoporous metal foam plates within the framework of isogeometric analysis (IGA) and higher-order plate theory. The nonlocal strain gradient theory (NSGT) taking into account the length scale and nonlocal parameters has been adopted to establish a scale dependent model of metal foam nanoscale plates. Von Karman nonlinear strains are then used to take up the geometric nonlinearity. Different pore dispersions, namely uniform, symmetric and asymmetric, are confirmed. By using the principle of virtual work, nonlinear governing equations are derived and then solved by using an isogeometric analysis and iterative Newton-Raphson method. Influences of the length scale parameter, porosity distributions, nonlocal parameter and nanoporous coefficient on the nonlinear deflection of the plate are numerically experimented in detail. Some findings would play an important role for designing metal foam structures.

Pyrolytic carbon (PyC) plays a critical role in many applications for its unique properties. In ceramic composite systems, the elastic properties of PyC at the fiber/matrix interface drive toughening mechanisms, enabling structural performance at increased operating temperatures. PyC expresses a wide range of crystallographic texture depending on fabrication parameters. As a result, modelling and optimization requires direct understanding of the texture-property relationships at the relevant length scales. This research leverages high-resolution transmission electron microscopy (HRTEM) to link the PyC microstructure to the elastic response observed via digital image correlation (DIC) during micropillar compression. The HRTEM and DIC results quantitatively resolve a gradient for microstructural texture and Young's modulus respectively, showing that disordered texture increases compressive stiffness normal to the average orientation of the PyC basal planes. The values for modulus ranged from 55 to 150 GPa, which are large compared to most experimental methods, but may be more realistic considering the uniaxial stress state and length scale. The behavior supports findings from numerical homogenization models, suggesting that this advanced technique may provide a path forward for optimization and validation of these nanoscale elasticity models.

In this paper, the free vibration of one-dimensional (1D) piezoelectric quasicrystal (PQC) microbeam is investigated. Varies shear displacement models for the PQC microbeam are developed. The modified couple stress theory with two material length scale parameters for PQC microbeam is used to capture the size effect of the phonon and phason fields. The differential quadrature method (DQM) is adopted to solve the equations of motion for the PQC microbeam, which is derived by the Hamilton's principle. Numerical results for the vibration of the 1D PQC microbeam are calculated. The effects of the geometry, electric voltage, material length scale parameter and boundary conditions on natural frequency of the PQC microbeam are demonstrated.

This manuscript presents a study of hydrogen-enhanced methane flames in a compact mesoscale burner array, where even a minute addition of hydrogen can significantly improve flame stability with reduced combustion length scale thereby enabling volumetric flexibility in small-scale combustion systems. The effect of hydrogen enhancement is demonstrated through combustion reaction length scale and operation limit analysis using methane fuel. The added hydrogen lowered lean blow off equivalence ratios, increased flame temperatures, and shorten the flame length scale, ultimately producing a denser flame array. 10 kHz OH∗ chemiluminescence and OH planar laser induced fluorescence imaging techniques were used to estimate heat release rate and visualize flame structures. Hydrogen addition increased the OH intensity and decreased global heat release rate fluctuation, and also showed more stable operation under acoustic perturbations. Hydrogen enhancement can be a promising solution for reducing geometric constraints and improving operating capabilities for compact propulsion and power generation systems.

A low carbon hypoeutectoid steel (0.19 wt% C) with proeutectoid ferrite and pearlite dual-components was subjected to surface plastic deformation via pipe inner surface grinding (PISG) at room temperature. The deformation microstructures for each component were systematically characterized along depth, and the patterns of structural evolution toward nanometer regime as well as the governing parameters were addressed. Proeutectoid ferrite grains were refined down to 17 nm, and the pattern covering a length scale of 4–5 orders of magnitude from micron- to nanometer-scale follows: formation of cellular dislocation structure (CDS), elongated dislocation structure (EDS), ultrafine lamellar structure (UFL) and finally the nanolaminated structure (NL). The pearlite experiences the deformation and refinement, and finally the transforming the ultrafine pearlite (UFP) into nanolaminated pearlite (NLP) with the ferrite lamellae as thin as 20 nm. Refinement for both UFL (UFP) and NL (NLP) can be realized via forming novel extended boundaries within ferrite lamellae. A critical lattice curvature of ∼2.8° is required for forming such extended boundary, corresponding to a minimum strain gradient of 0.25 μm−1 for a 100 nm-thick lamella. Refinement below size limit (expressed by lamellar thickness dT in nm) is correlated with the strain gradient (χ, in μm−1) by: d T = 12.5 χ . Refinement contributions from strain gradient caused by PISG processing and material heterogeneity were discussed.

In this research paper, as initial endeavors, the vibrational responses of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) nanoplates taking into account the effect of nonlocal parameter and strain gradient coefficient are investigated. The study aims at developing mathematical modeling via an analytical solution to FG-CNTRC nanoplate structure with allowance for the nonlocal strain gradient effect. The four types of CNT distribution are used and compared in the context of the vibration of nanoplate in the presence of the small length scale effects, namely the (a) UD, (b) FG-V, (c) FG-O, and (d) FG-X. Some theoretical equations based on the first-order shear deformation plate theory (FSDT) are presented to provide a lucid understanding of how the small length-scale influences the FG-CNTRC nanoplate. For the vibrational analysis of a nanoplate, which is simply supported boundary condition, Navier solutions are obtained. Also, in contrast to earlier studies, an analytical approach is used to establish the governing equations of the FG-CNTRC nanoplate. Some specific numerical examples are given and compared with the results presented in the literature. In the section of numerical results, the influence of the nonlocal parameter, strain gradient coefficient, geometric parameters and vibrational modes on the non-dimensional natural frequency are investigated and discussed in detail. These could be useful to analysts and designers to estimate the fundamental natural frequencies in each of the four CNT distributions that the FG-CNTRC nanoplate possesses.

In this work, a mathematical model is developed based on Griffith’s crack theory while incorporating couple stress and surface elasticity in order to examine the performance and operability of cracked vibrating beam micro/nanogyroscopes. A size dependent crack severity factor is used to represent increased local flexibility due to surface crack. The gyroscope size is decreased from micro- to nano-scale to analyze the effects of a driving side surface crack on the sensitivity of micro/nanogyroscopes. The static pull-in, natural frequencies, nonlinear frequency response, and gyroscope sensitivity that are calculated using the size dependent crack severity are compared to the results obtained using the classical crack severity factor. This allows for the determination of the length scale, in which size dependency must be considered in the crack severity. It is found that size dependent effects significantly increase the crack severity in nanogyroscopes leading to significant changes in the sensor’s sensitivity in comparison with the classical crack severity.

In advanced ceramics, improving toughness usually relies on the introduction of a soft metallic or polymeric ductile phase, which decreases the mechanical properties. Some natural materials are strong, stiff and tough due to a combination of mechanisms operating at different length scales. However, such structures have been extremely difficult to replicate into synthetic materials. Here we investigate the microstructure and the micromechanical properties of a bioinspired ceramic-ceramic composite. The micromechanical properties at room temperature show slight differences as a function of the platelet orientation. The hardness strongly decreases with increasing temperatures (up to 550 °C) for all the investigated orientations. The elastic strain to failure, defined as the H/E ratio, was used to estimate the wear resistance of materials, which is higher at room temperature because the dislocation mobility is lower than that at high temperature.

This work deals with the development of quantitative correlations of hydrogen evolution performance with solidification microstructural and thermal parameters in Al–1Sn, Al–2Sn, Al–1Fe, and Al-1.5Fe [wt.%] alloys. The cellular growth as a function of growth and cooling rates is evaluated using power type experimental laws, which allow determining representative intervals of microstructure length scale for comparison purposes with the results of immersion tests in 5 wt%NaOH solution. For both Al alloys systems, hydrogen evolution becomes slower as the alloy solute content increased. However, for a given alloy composition, whereas a more homogeneous distribution of Sn-rich particles promotes faster hydrogen generation using Al–Sn alloys, coarsening of Al6Fe IMCs (intermetallic compounds) fibers favors hydrogen production using Al–Fe alloys. When solidification conditions that result in a range of cellular spacings within 16 and 19 μm are considered, the specific hydrogen production of the Al-1wt.%Fe alloy is higher than that of the other studied alloys.

The present paper investigates the nonlinear static bending behavior of infinite length cylindrical panels made of functionally graded porous (FGP) materials. The shell with clamped edges is subjected to uniform temperature rise and transverse pressure loading. Thermomechanical properties of the shell with even distributed porosities are temperature-dependent and are graded along the thickness. The principle of virtual displacement and nonlocal strain gradient theory (NSGT) are employed to derive the equilibrium equations of the shallow shell resting on nonlinear elastic foundation. The concept of physical neutral surface (PNS) and higher-order shear deformation theory are also included into the formulation. Using the uncoupled thermoelasticity and Donnell kinematic assumptions, three differential equations of the shell under thermomechanical loading are established. The nonlinear system of governing equations is solved for the shell with infinite length which is clamped on both straight edges and free at other curved edges. The two-step perturbation technique and Galerkin procedure are employed to derive analytical solutions for the thermal, mechanical, and thermomechanical responses of cylindrical panels. The important parameters governing the bending behavior of shells under thermal-mechanical coupling load are identified and discussed. Parametric studies are given to show the influences of nonlocal/length scale parameter, porosity coefficient, foundation stiffness, geometrical parameter and functionally graded pattern. It is shown that the geometrical parameters have an important role on the bending behavior of cylindrical panels. Also, the temperature dependence of material properties results in higher deflection of the heated shells.

Graphical abstract, In the past years, a significant amount of effort has been directed at the observation and characterisation of caries using experimental techniques. Nevertheless, relatively little progress has been made in numerical modelling of the underlying demineralisation process. The present study is the first attempt to provide a simplified calculation framework for the numerical simulation of the demineralisation process at the length scale of enamel rods and its validation by comparing the data with statistical analysis of experimental results. FEM model was employed to simulate a time-dependent reaction-diffusion equation process in which H ions diffuse and cause demineralisation of the enamel. The local orientation of the hydroxyapatite crystals was taken into account. Experimental analysis of the demineralising front was performed using advanced high-resolution synchrotron X-ray micro-Computed Tomography. Further experimental investigations were conducted by means of SEM and STEM imaging techniques. Besides establishing and validating the new modelling framework, insights into the role of the etchant solution pH level were obtained. Additionally, some light was shed on the origin of different types of etching patterns by simulating the demineralisation process at different etching angles of attack. The implications of this study pave the way for simulations of enamel demineralisation within different complex scenarios and across the range of length scales. Indeed, the framework proposed can incorporate the presence of chemical species other than H ions and their diffusion and reaction leading to dissolution and re-precipitation of hydroxyapatite. It is the authors’ hope and aspiration that ultimately this work will help identify new ways of controlling and preventing caries.

Finite elemen model for the structural behaviours of bi-directional (2D) FG porous microbeams based on a quasi-3D theory and the modified strain gradient theory (MSGT) is presented. As the main novelty of this study, in order to capture accurately the size effects, the MSGT is employed with three material length scale parameters (MLSPs) rather than the modifed couple stress theory (MCST) with only one MLSP. The material properties including three MLSPs are varied in both the axial and thickness directions as well as porosity. By using a quasi-3D theory, which inludes normal and shear deformations, the governing equations for static, vibration and buckling analysis are derived and solved by Hermite-cubic beam element for various boundary conditions. Through numerical examples, effects of variable MLSP and porosity as well as gradient index in two directions on the deflections, natural frequencies and buckling loads of 2D FG porous microbeams are examined.

We examine the diffraction dynamics of a two-dimensional (2D) detonation in a circular arc of the conventional HMX-based, high performance, solid explosive PBX 9501, for which the detonation reaction zone length scale is estimated to be of the order of 100–150 µm. In this configuration, a steady propagating detonation will develop, sweeping around the arc with constant angular speed. We report on results from three PBX 9501 arc experiments, exploring the variation in linear speed on the inner and outer arc surfaces for the steady wave along with the structure of the curved detonation front, as a function of varying inner surface radius and arc thickness. Comparisons of the properties of the motion of the steady wave for each arc configuration are then made with a spatially-distributed PBX 9501 reactive burn model, calibrated to detonation performance properties in a 2D planar slab geometry. We show that geometry-induced curvature of the detonation near the inner arc surface has a significant effect on the detonation motion even for conventional high explosives. We also examine the detonation driving zone structure for each arc case, and thus the subsonic regions of the flow that determine the influence of the arc geometry on the detonation propagation. In addition, streamline paths and reaction progress isolines are calculated. We conclude that a common approximation for modeling conventional high explosive detonation, wherein the shock-normal detonation speed is assumed equal to the Chapman–Jouguet speed, can lead to significant errors in describing the speed at which the detonation propagates.

Recently, PcBN tooling have been successfully introduced in machining Ni-based superalloys, yet our knowledge of involved wear mechanisms remains limited. In this study, an in-depth investigation of PcBN tool degradation and related wear mechanisms when machining Inconel 718 was performed. Diffusional dissolution of cBN is an active wear mechanism. At high cutting speed oxidation of cBN becomes equally important. Apart from degradation, tool protection phenomena were also discovered. Oxidation of Inconel 718 resulted in formation of γ-Al2O3 and (Al,Cr,Ti)3O4 spinel that were deposited on the tool rake. Also on the rake, formation of (Ti,Nb,Cr)N takes place due to cBN-workpiece interaction. This creates a sandwich tool protection layer forming continuously as tool wear progresses. Such in operando protection enabled counterbalancing tool wear mechanisms and achieved high performance of PcBN in machining.

We report the mechanism of acoustic-flame coupling for buoyant diffusion flame in droplets. The flame under acoustic excitation exhibits differential varicose and sinuous modes including partial extinction and pinch offs at certain shedding heights. Contrary to traditional buoyant flames, the diameter (d) regression of a droplet results in self-tuning of the instability modes with progression in burning times. In essence, we show that a droplet exhibits multi frequency response with advent of new oscillations modes at different points of the burning lifetime. The acoustic perturbations modulate the flame surface or heat release only at lower frequency bands by feeding energy into the natural vortical stability modes of a buoyant plume. Interestingly, we unearth that a flame is naturally unstable at all frequencies lower than g / d . Acoustic pumping at any such frequency ( g / d ) corresponds to a unique convective length scale h such that fflame = g / h . We therefore establish that the flame exhibits multiple convective length scales throughout the burning cycle. We subsequently established that the shedding length scale of the droplet flame shortens by more than 25% with increase in acoustic pressure. We theoretically proved that using critical circulation argument, one can uniquely determine the shedding length scale at any acoustic loading. However, it is interesting to note that while the acoustic pressure amplitude is crucial for determining the convective length at which a flame rolls up, the frequency of excitation has no role to play. In other words, the velocity field introduced by the acoustic pressure is responsible for the shedding of the flame. The acoustic perturbations also lead to bulk oscillation of the flame surface near the forward stagnation zone. This is attributed to the acoustic induced velocity that leads to transient shifting of the stoichiometric surface.

Pre-ignition is an undesirable ignition event that affects chemical kinetic measurements in chemical reactors. Meanwhile, it appears randomly in engineering systems and is highly relevant to the soft knock or much stronger and detrimental super-knock in modern downsized engines. Currently its origins are still not fully understood. In this study, the role of turbulence in pre-ignition phenomena was experimentally investigated using a novel rapid compression machine. Different turbulent flow fields were achieved through calibrated orifice plates. Stoichiometric isooctane/air mixtures were tested under engine-relevant conditions in a target pressure range of 15–50 bar and a temperature range of 720–860 K. Useful insights into pre-ignition mechanism were obtained by combining instantaneous pressure acquisition with simultaneously recorded high-speed imaging. The experimental results demonstrate that owning to turbulent mixing with colder boundary layers, ignition timing is delayed when compared to ideal homogeneous compression ignition scenarios. However, pre-ignition phenomena can still be observed and become pronounced at lower target pressures with longer ignition delays. Moreover, pre-ignition formation can be characterized by single or multiple spherical flame kernels, distributed discretely inside core mixture or at near-wall regions. Different from the auto-ignition scenarios dominated by the chemical reactivity of test mixture, these pre-ignition flame kernels feature standard deflagration propagation. Finally, a dimensionless scaling analysis shows that pre-ignition formation is closely associated with turbulent length scale and laminar flame thickness.

The coupling of CFD simulations with detailed chemical kinetics presents great progress in predicting the complex behavior of reacting flows, but also requires validated input parameters in the form of experimental data. The spatial profile of a combustion wave represents one such parameter, which can be directly measured using chemiluminescence imaging of a spherically expanding flame. In this work, emission signals from electronically excited methylidyne (CH*) and hydroxyl (OH*) radicals near 434 nm and 315 nm, respectively, from spherically expanding methane–air flames at 1 atm and 298 K were recorded for equivalence ratios of 0.8, 1.0, and 1.2. Spatial profiles of normalized intensity were compared to predicted profiles from AramcoMech2.0. The effect of image resolution was investigated by repeating experiments for three levels of image pixel density. An Abel inversion was employed to extract intensity profiles of CH* and OH* at flame radii up to 6.5 cm. Measured flame thickness increased as flames grew in size, but this behavior diminished as image resolution increased. A linear stretch correlation was used to extrapolate measured thicknesses to an unstretched thickness for each experimental condition. Radical-based flame thicknesses and corresponding spatial profiles were found to be highly dependent on image resolution, and at high resolution, measured flame thickness appeared to approach the kinetically predicted radical-based thicknesses. This paper lays the foundation for future, comprehensive measurements of spherical, laminar flames that can resolve the flame zone details to a level of precision not typically seen in the literature, providing benchmark data for both kinetics model validation and CFD model inputs. As a result, the measurements thus far indicate that the measured flame zone thickness based on electronically excited species is much closer to the length scale typically predicted by kinetics models than what has been seen in most experiments to date.

The surface of turbulent premixed flames is fractal within a finite range of scales and the fractal dimension and inner cutoff scale are key components of fractal turbulent combustion closures. In such closures, the estimate for the surface area is sensitive to the value of the inner fractal cutoff scale, whose modeling remains unclear and for which both experimental and numerical contradictory evidence exists. In this work, we analyze data from six direct numerical simulations of spherically expanding turbulent premixed flames at varying Reynolds and Karlovitz numbers. The flames propagate in decaying isotropic turbulence and fall in the flamelet regime. Past an initial transient, we find that the fractal dimension reaches an asymptotic value between 2.3 and 2.4 in good agreement with previous results at similar conditions. A minor dependence of the fractal dimension on the Reynolds and Karlovitz numbers is observed and explained by the relatively low values of the Reynolds number and narrow inertial and fractal ranges. The inner fractal cutoff scale Δ* is found to scale as Δ * / l ∼ Re λ − 1.14 , where l is the integral scale of turbulence and Reλ is the Reynolds number based on the Taylor micro-scale computed in the turbulence on the reactants’ side. The scaling is robust and insensitive to the Karlovitz number over the range of values considered in this study. An important implication is that the ratio Δ*/η grows with Reynolds number (η is the Kolmogorov scale), albeit at a rather slow rate that may explain the widespread observation that 4 ≤ Δ*/η ≤ 10. This suggests that Δ*, although smaller than λ, is not a dissipative length scale for the flame surface and scaled solely by η. Finally, a dissipative threshold scale that remains constant once normalized by η is identified.

International audience; We experimentally investigated the packing of wet monodisperse spheres with controlled falling height. The packing fraction are found to decrease with smaller grain size and free fall heights. A model describing the effects of interparticle force and falling height on packing fraction is developed by introducing a dimensionless length scale, representing the extent of particle rearrangement towards a denser state due to impacts of falling grains. A universal law is observed for both wet particles where capillary forces dominate and dry powders where van der Waals forces govern the packing behaviour. This study deepens the understanding of packing of cohesive spheres and provide a simple experimental method for generating granular media with tailored packing fraction.

The influence of crack curvature radius and plastic properties of material on the crack tip fields is evaluated by conventional mechanism-based strain gradient (CMSG) plasticity theory, and classical plasticity theory. Stress fields in single edge tension specimen are investigated numerically for a wide range of the crack curvature radius variations. The strain hardening exponent varied from N=0.075 to N=0.4. The local areas of the influence of the crack tip curvature radius are established for the strain gradient plasticity and classical plasticity. The couple effects of material length scale parameter and plastic properties of material on crack tip fields are established for strain gradient plasticity. The boundaries of CMSG plasticity dominated zone are determined.

The effect of initial turbulence specifications at intake valve closure (IVC) on combustion in a compression ignition engine is studied through CFD simulations. The objective of this study is to understand the importance of the turbulence specifications for closed cycle simulations. Simulations are conducted using AVL – FIRE engine simulation program with DME as the fuel and ECFM-3Z as the combustion model. Results from simulations indicate that, for the conditions tested, the initial turbulence does not have any significant influence on the pressure trace. A higher initial turbulent kinetic energy and larger turbulent length scale leads to a higher temperature at the start of injection (SOI) and, consequently faster ignition and higher NO emissions. In contrast, the effect on turbulent time scales after injection is negligible.

Torsional micro-rods are key components in many micro-sensors and micro-resonators in aviation industry but in the literature proposed models have usually circular cross section which can be a limitation. In the torsional vibrations of micro-structures with non-circular cross section shape, the displacement fields and governing equations are completely dependent on the cross section shape of the structure which makes the analysis procedure more complicated. The aim of this study is to demonstrate the impact of geometrical parameters of the micro-rod especially its cross section shape, the type of medium and the presence of the external fields such as magnetic field in the torsional vibration behavior of the micro-rod. For this purpose, using the Hamilton's principle, the governing equation of the torsional vibration of the micro-rod with non-circular cross section embedded on elastic medium in the presence of a magnetic field is derived. To show the effects of size dependency of the micro-rod, modified couple stress theory is used. For instance, elliptical and rectangular cross section shapes with the same area are chosen for a micro-rod. After calculating the natural frequency of the micro-rod by the Galerkin method, the effect of cross section shape on the non-dimensional natural frequency of the micro-rod is investigated for changes in the aspect ratio of the cross section. In addition, the influence of length scale parameter, stiffness of torsional medium and magnetic field permeability on the natural frequency of the micro-rod are evaluated. The obtained results demonstrate that the natural frequency of the micro-rod is completely affected by the shape and aspect ratio of the cross section. These results can be useful in the micro-structure design stage. Also, a comparison is made between the obtained analytical results and those of semi-analytical differential transform method (DTM).

The response of Martian nonmigrating tidal perturbations in the thermospheric and ionospheric densities to solar minimum, as contrasted with their behavior in the solar declining phase, is investigated using five years of data collected by the Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite. We find that the average tidal amplitudes, expressed as the percent variation of the neutral and electron densities from their respective average background values, are larger (by a factor of ~1.3 above 170 km) during solar minimum compared to the declining phase of the solar cycle. These larger amplitudes, on the dayside, may be due to a decrease in the atmospheric scale height, which for neutral argon averaged over a Martian year, goes from 12.5 km during declining phase, to 10.5 km for solar minimum. An additional controlling factor is that the average vertical dissipation length scale becomes shorter, going from ~34 km during the declining phase to ~29 km at solar minimum. On the nightside, the amplitude of the neutral atmospheric tides is similar between the declining phase and solar minimum. There are changes in the length scales, with the average night side scale height becoming somewhat greater during solar minimum, as well as an increase in the dissipation length scale. Dayside tidal perturbations in the ionosphere at ~145 km to ~170 km exhibit the expected amplitude relation predicted by simplified photochemistry for the observed neutral perturbation amplitudes as well as strong correlation with the longitudinal neutral density perturbations. Interpretation of the data are faced with the complication of limited coverage between season, latitude, and local times together with long temporal baselines that may mix different tidal modes; discussion on the possible role of the latitude effect on amplitude are discussed. The results of the study are put into context of a hypothesis on how tidal amplitudes might be expected to change in response to solar minimum.

In this paper, the finite element discretization of non-classical continuum models with micro-inertia is analysed. The focus is on micro-inertia extensions of the one-dimensional rod model, the beam bending theories of Euler-Bernoulli and Rayleigh, and the two-dimensional membrane model. The performance of a variety of mass matrices is assessed by comparing the natural frequencies and their modes with those of the associated discrete systems, and it is demonstrated that the use of higher-order mass matrices reduces errors and improves convergence rates. Furthermore, finite element sizes larger than the corresponding physical length scale are shown to be sufficient to capture the natural frequencies, thus facilitating numerical models that are not only reliable but also computationally efficient. The authors acknowledge support from MCIN/ AEI/10.13039/501100011033 under Grants numbers PGC2018-098218-B-I00 and PRE2019-088002. FEDER: A way to make Europe. ESF invests in your future.

This article focuses on predicting the instant of failure in a real scale component of complex geometry and loading using a ductile damage model calibrated exclusively on small-scale laboratory specimens of relatively simple shape. The ductile behaviour of a strain hardened aluminium alloy AA1050, formed into a thin-walled component, is modelled by a coupled ductile fracture locus model presented in a recent study ( Baltic et al., 2020 ). The component is exposed to high internal pressure and has a safety vent designed for safe pressure handling. The extensive plastic deformation in the safety vent leads to localised ductile failure occurring at a limit load. The pertaining material parameters were calibrated solely from basic ductile fracture experiments in the preceding work ( Baltic et al., 2020 ), where the bottom section of the thin-walled component was machined into notched and shear samples to characterize different states of stress and to construct a well-defined fracture locus. Although the calibrated material model relies on the local fracture strain measurements, it involves a regularization as a function of the length scale defined as a width of the observed localisation band from Digital Image Correlation (DIC) analysis. In the current study the calibration on small-scale specimens is complemented by a large-scale specimen to determine the length scale correction crucial for capturing the correct width of the localisation band in the analysed structure. This is necessary because the failure initiation zones of the calibration specimens and the real size structure, i.e. their gauge lengths where the localisation band appears, vastly differ in size. Finite element (FE) model results are compared to measurements of the deformation of the aluminium component under pressure and maximum load prior to failure. The numerical and experimental results show an excellent agreement and consistent fracture predictions for various mesh discretizations.

Large eddy simulation (LES) with dynamic Smagorinsky model (DSM) has been implemented to elicit the turbulence characteristic of the flow inside a cubic lid-driven cavity at Reynolds number of 10000. The coherent organized structures tear, pair and disintegrate leading to the evolution of turbulence. They are reflected in the RMS (root mean square) plots of the turbulent fluctuations in different planes. The flow has a near zero helicity value; unlike the other two velocity component, the probability density function of span wise velocity component shows the flow symmetry on the both side of the mid plane in span wise direction; kurtosis being largely leptokurtic except near wall locations indicates their peakedness. The quadrant analysis shows presence of more coherent structures near the down stream wall and the joint probability distribution function shows that turbulence is anisotropic. Power spectra is observed to follow the − 5 ∕ 3 law. Both Taylor microscale λ and Kolmogorov length scale η show greater near-wall dissipation

A size-dependent plate model is developed to investigate the elastic responses of the multilayered two-dimensional quasicrystal nanoplates based on the nonlocal strain gradient theory for the first time. A nonlocal stress field parameter and a length scale parameter are taken into account in the new model to capture both stiffness-softening and stiffness-hardening size effects. The exact solution for a single-layer two-dimensional quasicrystal simply supported nanoplate is derived by utilizing the pseudo-Stroh formalism in conjunction with the nonlocal strain gradient theory. Afterward, a dual variable and position method is used to deal with the multilayered case. Numerical examples are presented to study the dependence of size-dependent effect on nanoplate length and the influences of scale parameters on the quasicrystal nanoplate subjected to a z-direction mechanical load on its top surface. The proposed model should be useful to verify various nanoplate theories and other numerical methods.

Two-dimensional materials with self-similar second-order hierarchy are considered. The microstructure with fourfold cubic symmetry is generated by a periodic system of voids in brittle parent material, in one case, macrovoids are filled by a microvoided phase, and in the second one, this phase surrounds hollow macrovoids. A crack is embedded in a rectangular periodic domain subjected to the K-field boundary conditions, and the fracture toughness is determined by the analysis of stresses in the crack-tip vicinity. A novel approach based on the discrete Fourier transform reduces the computational cost of the problem. The analysis of the domain, consisting of several hundreds repeating patterns, is reduced to the multiple analysis of a single representative cell in the Fourier transform space. A parametric study is carried out and, in particular, the influence of parent material redistribution between the hierarchical levels is examined. It is found that for the material with filled macrovoids increasing the relative stiffness at the second hierarchical level diminishes the fracture toughness, while for the second layout the effect is opposite. A comparison with non-hierarchical voided materials of the same relative density emphasizes the role of the length scale parameter of a layout.

In phase field methods for fracture, versatility is acquired at the cost of the addition of a new parameter, a length scale parameter. The length scale parameter affects notch sensitivity, which in cellular materials is typically related to lengths of the material microstructure. Here, the relation between this length scale parameter and observable microstructural lengths of a cellular material is investigated numerically, specifically lengths derived using statistical geometry of random Voronoi tessellations. It is found that the fracture load of a homogeneous continuum model (i.e. a macroscopic model) coincides with that of a microstructured model if the length scale parameter is chosen to be the same in both models, while approximate macroscale stiffness and energy release rate are obtained by scaling the properties of the microstructured model with powers of the relative density. The correlation between the micro- and macroscale models is best when the length parameter is chosen as approximately two to three times the average cell size of the microstructure, depending on the relative density – which is also equal to approximately eight times a critical defect length of the Voronoi tessellation, regardless of relative density – as the microstructured material then behaves more like a continuum. If the length scale parameter needs to be smaller than twice the cell size or five times the critical length, the crack path is sensitive to features in the microstructure, and continuum modelling of the porous material cannot be advised.

Materials with certain heterogeneous microstructures have been shown to hold a synergistic combination of strength and ductility. In this study, we demonstrate novel transformation pathways for creating such heterogeneous microstructure in Ti-alloys by integrating thermodynamic databases with phase field simulations. The results show that the concentration modulations at different length scales produced by (a) precursory spinodal decomposition in the parent phase and (b) interdiffusion in multi-layers having different alloy compositions can generate effectively hierarchical and gradient α + β two-phase microstructures, with a mixture of fine α precipitate regions and α precipitate-free-zones or coarse α precipitate regions. The novel microstructures produced include “inverted globular α” bi-modal microstructures and gradient microstructures with controlled spatial gradients in particle size and number density of α precipitates. This study may shed light on how to design novel hierarchical and gradient two-phase microstructures with tunable size and density of precipitates as well as the length scale of their spatial heterogeneity for desired properties.

The influence of severe plastic deformation on the relaxation dynamics of a Pd40Ni40P20 (at.%) bulk metallic glass was investigated on the atomic length scale by X-ray photon correlation spectroscopy and fluctuation electron microscopy. At a series of isothermal temperatures adjusted by step heating below the glass transition, the relaxation times were obtained by X-ray photon correlation spectroscopy and the corresponding activation energies were evaluated. It was found that the relaxation dynamics was accelerated by about a half order of magnitude after plastic deformation by high-pressure torsion processing, which indicates that effective rejuvenation has occurred. At relatively low temperatures the relaxation process was stress-dominated and deformation could improve the atomic mobility without changing the energy barrier. At higher temperatures, a second regime of relaxation times occurred. It is concluded that with increasing temperature, a crossover from a stress-dominated to a diffusion-dominated relaxation process occurs. Moreover, the medium range order was measured using variable resolution fluctuation electron microscopy indicating that deformation-induced changes in topology are responsible for the rejuvenation and the accelerated dynamics.

Bones are structurally heterogeneous organs with diverse functions that undergo mechanical stimuli across multiple length scales. Mechanical characterization of the bone microenvironment is important for understanding how bones function in health and disease. Here, we describe the mechanical architecture of cortical bone, the growth plate, metaphysis, and marrow in fresh murine bones, probed using atomic force microscopy in physiological buffer. Both elastic and viscoelastic properties are found to be highly heterogeneous with moduli ranging over three to five orders of magnitude, both within and across regions. All regions include extremely compliant areas, with moduli of a few pascal and viscosities as low as tens of Pa·s. Aging impacts the viscoelasticity of the bone marrow strongly but has a limited effect on the other regions studied. Our approach provides the opportunity to explore the mechanical properties of complex tissues at the length scale relevant to cellular processes and how these impact aging and disease.

This study presents a size dependent model using the higher-order shear deformation theory (HSDT) in conjunction with modified strain gradient theory (MSGT) for free vibration analysis of functionally graded (FG) anisotropic microplates. The FG anisotropic material is made of hexagonal beryllium crystals which can be considered as a hexagonal one. To consider size effects, three material length scale parameters (MLSPs) are added into the elastic constants of the anisotropic material. Based on the principle of virtual work, discretized governing equations of the FG hexagonal microplates are obtained. Subsequently, the natural frequency of the FG anisotropic microplates is determined by using isogeometric analysis (IGA). Numerical results show that the natural frequency of the FG anisotropic microplates is influenced by the geometry, boundary condition, length-to-thickness ratio, exponential factor and material length scale parameter. The results of classical HSDT model can be restored from the present model when three MLSPs equal to zero. Moreover, the differences of the natural frequency predicted by MSGT and classical HSDT can grow up more than 4.5 times.

Within the framework of three-dimensional (3D) nonlocal elasticity theory, the authors develop an asymptotic theory to investigate the free vibration characteristics of simply supported, single-walled carbon nanotubes (SWCNTs) non-embedded or embedded in an elastic medium using the multiple time scale method. Eringen’s nonlocal constitutive relations are adopted to account for the small length scale effect in the formulation. The interactions between the SWCNT and its surrounding medium are modeled as a two-parameter Pasternak foundation model. After performing a series of mathematical processes, including nondimensionalization, asymptotic expansion, and successive integration, etc., the authors obtain recurrent sets of motion equations for various order problems. The nonlocal classical shell theory (CST) is derived as a first-order approximation of the current 3D nonlocal elasticity problem, and the equations of motion for higher-order problems retain the same differential operators as those of the nonlocal CST, although with different nonhomogeneous terms. The current asymptotic solutions for the natural frequency parameters of non-embedded or embedded SWCNTs and their corresponding through-thickness modal stress and displacement component distributions are obtained to assess the accuracy of various nonlocal shell and beam theories available in the literature.

Multi-length scale modeling is performed to (i) predict the carburized case depth of SAE8620 steel gears by solving the Fick’s second law of diffusion, (ii) model the martensitic microstructure evolution in a grain inside the carburized case as well as to study the effect of stress cycling on retained austenite (RA) and martensite using a 3D phase-field model, (iii) simulate the effect of carburization and different RA contents on macroscale fatigue behavior of SAE8620 steel spur gear using the finite element method. The diffusion model predicts that the case depth increases with increasing heat treatment time and temperature. The phase-field simulations show that RA can transform to martensite during fatigue loading, where the extent of the transformation will depend on the type of stresses applied, i.e. stresses in a high stress regime or low stress regime of fatigue loading. Reverse transformation of martensite to austenite is also observed in low RA sample under high stress regime. The macroscale simulations show that the carburized case with high RA gives rise to better fatigue life compared to that with low RA.

The deformation and strengthening behaviors of face-centered cubic/face-centered cubic (fcc/fcc) nickel (Ni)/aluminum (Al) nanolaminates were systematically investigated in uniaxial compression tests using micropillars with a varied range of individual layer thickness h from 5 nm to 100 nm. The deformation behavior of micropillar samples of Ni/Al nanolaminates was strongly dependent on the individual layer thickness of Ni and Al, where at larger h the deformation of micropillars took place first by plastic deformation of the Al layers and proceeded to dislocation pileup–based Hall–Petch (H-P) strengthening, which further nucleated in the Ni layers. The deformation behavior of the Ni/Al nanolaminates transitioned from dislocation-dominated homogeneous co-deformation with multiple shearing in Ni and Al layers and grain boundary–mediated massive fractures in the Ni layers at larger h to stress-concentrated broken interfaces and valleys with plastic barreling due to layer shearing and smaller fractures in the Ni and Al layers at smaller h. With decreasing h from 100 nm down to 5 nm, the Ni/Al micropillars exhibited a gradual transition from lower to higher strain hardening, and the strain-hardening rate reached a peak at h = 20 nm; while it started declining with further decreasing of h. The yield strength (σ0.2%) and flow strength (σ8%) of the Ni/Al micropillars reached the peak of ~1.93 GPa and ~2.35 GPa, respectively, with decreasing h to 10 nm. The confined layer slip (CLS) strengthening mechanism operated well at h = 10 nm, whereas H-P strengthening model was applicable for h = 20–100 nm, and surprisingly the strengthening at h = 5 nm was independent of h. Interestingly, significant strain softening was observed at h = 5 nm due to the severe plastic deformation at the broken interfaces, interfacial sliding of layers, and defects related to the presence of intermixed Ni and Al layers at the interface, and valleys between the islands of stacked constituent layers.

The stiff film/compliant substrate composite structure with a high modulus ratio finds a wide range of applications in production and in scientific research, and its indentation behavior cannot be described by the traditional theory when the film thickness is reduced from the millimeter scale to the micrometer or nanometer scale. In order to better understand the trans-scale indentation response of the composite structure caused by the reduction in the film thickness, this problem is solved analytically with the strain gradient theory and integral transformation. The gradient effect on the indentation response of the system is assessed in detailed from three aspects: load-displacement relationship, surface topography and distribution of bending moment on the film. In addition, the influences of film thickness, modulus ratio of the film to the substrate, contact radius and Poisson's ratio on the gradient effect are investigated. It is found that the gradient effect on the indentation response of the system, which is not sensitive to the contact radius and Poisson's ratio, is related not only to the film thickness but also to the modulus ratio of the film to the substrate. Based on the above analysis, a dimensionless number (g/l) is proposed to evaluate the gradient effect on the indentation behaviors of the system. And with the help of the dimensionless number, a new simple and accurate method for measuring the material length scale is proposed. Our research provides a theoretical basis for an in-depth understanding of the gradient effects on the indentation response of the stiff film/compliant substrate system and for the measurement of the material length scale.

In this work, we present the results from multi-length-scale studies of a Mn-Na-W/SiO2 and a La-promoted Mn-Na-W/SiO2 catalyst during the oxidative coupling of methane reaction. The catalysts were investigated from the reactor level (mm scale) down to the single catalyst particle level (μm scale) with different synchrotron X-ray chemical computed tomography techniques (multi-modal chemical CT experiments). These operando spatially-resolved studies performed with XRD-CT (catalytic reactor) and multi-modal μ-XRF/XRD/absorption CT (single catalyst particle) revealed the multiple roles of the La promoter and how it provides the enhancement in catalyst performance. It is also shown that non-crystalline Mn species are part of the active catalyst component rather than crystalline Mn2O3/Mn7SiO12 or MnWO4.

In metallic materials, the activation of one slip system increases the flow strength of other slip systems, which is phenomenon known as latent hardening. This latent hardening behavior has been understood by the “forest hardening” mechanism arising from mutual dislocation interactions at the continuum length scale. As the size of a sample decreases to the submicron scale, the interactions between dislocations become increasingly sparse, so plastic deformation is instead governed mainly by dislocation sources. In this paper, we use three-dimensional dislocation dynamics (DD) simulations to examine plastic deformation in single crystalline Cu micropillars subjected to two types of combined loading conditions: tension after torsion and torsion after tension. These combined loadings are then compared with simple tension and pure torsion, respectively. We find that there exists a transition from latent hardening to latent softening in 600 nm samples undergoing tension after torsion. The systematic computational and theoretical model described here suggests explosive multiplication causes dislocation density to greatly increase, giving rise to latent softening in those micropillars under tension after torsion.

This work focuses on studying the oscillating length scale of gas pipeline leakage flame restricted by parallel sidewalls with various separation distances. A series of experiments are conducted with 3, 6 and 10 mm nozzles and propane is used as fuel. Results show that reduction of the sidewall separation distance hinders the air entrainment, and provokes significant enlargement of the oscillation amplitude. Besides, the oscillating length scale of propane jet fire is also found to increase with the fuel flow rate. Finally, a new physical model, based on the scaling analysis of the fuel flow field and previous work, is proposed to characterize the variation of oscillating length for the restricted propane jet fire. The results obtained in this work and in previous studies, correlate with a better agreement using the present model than a previous suggested model. This work is not only a significant supplement to the flame oscillation instability physics from previous results for the flame restricted by parallel sidewalls, but also can provide some scientific basis to the design and management on the gas fuel energy storage and transportation systems in the cities to reduce the possible fire thread to the surrounding buildings.

Hypothesis: Previous works have shown that many-body interactions induced by dispersants with increasing correlation length will generate a diminishing two-phase region [Soft Matter 14, 6921 (2018)]. We conjecture that the attenuation of the depletion attraction due to many-body interactions is a ubiquitous phenomenon in medium-induced interactions. We propose mixtures of colloidal particles and rod-like polymers as a feasible experimental system for verifying these predictions, since the intra-molecular correlations are not screened in a good solvent for rod-like polymers as they are in flexible polymers. The length of the rods can grow and become the dominant length scale that determines the range of the depletion interactions for the imbedded non-adsorbing particles. Simulations: We study many-body depletion forces induced by polymerizing rod-like polymers on spherical non-adsorbing colloids, using Metropolis Monte Carlo simulations. We also employ a simple mean-field theory to further justify our numerical predictions. Findings: We demonstrate that the phase diagram displays the same qualitative features that have previously been predicted by many-body theory, for mixtures containing flexible polymers under theta solvent conditions. The contraction of the particle two-phase region that we observe, as the correlation length increases beyond some specific value, could be a signature of the weakening of the depletion caused by many-body effects.

Nuclear magnetic resonance (NMR) structure refinement is inherently integrative. The refinement incorporates a multitude of experimental data and minimizes the difference between observed and calculated values. Here, we review how the integrative use of non-NMR measurements, in particular, distance restraints from Förster resonance energy transfer and cross-linking coupled with mass spectrometry, can augment NMR depiction of protein structure and dynamics. Refinement against both NMR and non-NMR distance restraints helps to characterize the structures of high-molecular-weight proteins and protein complexes. When a protein fluctuates among multiple conformations at millisecond or a faster timescale, NMR signals from the different conformational states may coalesce into a single set of peaks. The integration of non-NMR distance restraints facilitates the deconvolution of NMR observables to state-specific restraints. Furthermore, the integrative use of fluorescence measurements, which provides an assessment of both length scale and timescale of protein dynamics simplifies protein ensemble structure refinement otherwise with NMR restraints alone and affords a more wholesome picture of protein dynamics. Together, distance measurements are intuitive and easy to implement by using an appropriate pseudoenergy function. Future development shall involve more accurate modeling of paramagnetic and fluorescent probes, incorporation of sparse restraints from new techniques, and characterization of protein structures in a complex cellular environment.

Limited studies have been conducted to establish scaling relationships of soil reaction forces and length scales of bulldozer blades using the Discrete Element Method (DEM) technique. With a DEM-based similitude scaling law, performance of industry-scale blades can be predicted at reduced simulation efforts provided a calibrated and validated DEM soil model is developed. DEM material properties were developed to match soil cone penetration testing. The objectives of the study were to develop a DEM soil model for Norfolk sandy loam soil, establish a scaled relationship of soil reaction forces to bulldozer blade length scales (n = 0.24, n = 0.14, n = 0.10, and n = 0.05), and validate the DEM-predicted soil reaction forces on the scaled bulldozer blades to the Norfolk sandy loam soil bin data. Using 3D-scanned and reconstructed DEM soil aggregate shapes, Design of Experiment (DOE) of soil cone penetration testing was used to develop a soil model and a soil-bulldozer blade simulation. A power fit best approximated the relationship between the DEM-predicted soil horizontal forces and the bulldozer blade length scale (n) (R2 = 0.9976). DEM prediction of soil horizontal forces on the bulldozer blades explained the Norfolk sandy loam soil data with a linear regression fit (R2 = 0.9965 and slope = 0.9634).

We derive a theoretical framework for the non-Newtonian viscosity of a sticky, attractive colloidal dispersion via active microrheology by modeling detailed microscopic attractive and Brownian forces between particles. Actively forcing a probe distorts the surrounding arrangement of particles from equilibrium; the degree of this distortion is characterized by the Peclet number, Pe≡Fext/(2kT/a), where kT is the thermal energy and a the probe size. Similarly, the strength of attractive interactions relative to Brownian motion is captured by the second virial coefficient, B2. We formulate a Smoluchowski equation governing the pair configuration as it evolves with external and attractive forces. The microviscosity is then computed via non-equilibrium statistical mechanics. For active probe forcing, the familiar hard-sphere boundary-layer and wake structures emerge as Pe grows strong, but attractions alter its shape: changes in relative probe motion arising from its attraction to the bath particles can lead to a high-Pe, strong-attraction flipping of the microstructure, where an upstream depletion boundary layer forms, along with a downstream accumulation wake. This highly distorted structure is analyzed at the micro-mechanical level, where changes in the time spent upstream or downstream from a bath particle lead to hypo- and hyper-viscosity. When attractions are strong, separating the interparticle microviscosity into contributions from attractions and repulsions reveals an attractive undershoot and a repulsive overshoot, as advection grows strong enough to break interparticle bonds downstream and drain the wake. In contrast to linear-response rheology that is predictable entirely by B2 for short-ranged attractions, here the non-Newtonian viscosity is not, owing to the additional length scale introduced by the boundary layer. The ratio of external to attractive forces eventually supersedes B2 as the relevant predictor of structure and rheology. This behavior may provide interesting connections to active motion in biological systems where attractive forces are present.