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The mechanical behavior of unsaturated porous media under non-isothermal conditions plays a vital role in geo-hazards and geo-energy engineering (e.g., landslides triggered by fire and geothermal energy harvest and foundations). Temperature increase can trigger localized failure and cracking in unsaturated porous media. This article investigates the shear banding and cracking in unsaturated porous media under non-isothermal conditions through a thermo–hydro–mechanical (THM) periporomechanics (PPM) paradigm. PPM is a nonlocal formulation of classical poromechanics using integral equations, which is robust in simulating continuous and discontinuous deformation in porous media. As a new contribution, we formulate a nonlocal THM constitutive model for unsaturated porous media in the PPM paradigm in this study. The THM meshfree paradigm is implemented through an explicit Lagrangian meshfree algorithm. The return mapping algorithm is used to implement the nonlocal THM constitutive model numerically. Numerical examples are presented to assess the capability of the proposed THM mesh-free paradigm for modeling shear banding and cracking in unsaturated porous media under non-isothermal conditions. The numerical results are examined to study the effect of temperature variations on the formation of shear banding and cracking in unsaturated porous media.

Extensive research has shown that nanolayered structures are capable of suppressing the shear banding in metallic glass in nanoindentation experiments. However, the specific mode and mechanism of the shear banding underneath the indenter remains unknown. Also, the quantification of shear banding-induced strain localization is still a challenge. Herein, the size-dependent shear banding behavior of a CuTiZrNb high-entropy alloy-based nanolayered glass with individual layer thicknesses (h) ranging from 5 to 80 nm was systematically investigated by nanoindentation tests. It was found that the hardness of the designed structure was almost size-independent. Yet, a clear transition in the deformation modes from the cutting-like shear bands to the kinking-like ones was discovered as h decreased to 10 nm. Moreover, multiple secondary shear bands also appeared, in addition to the primary ones, in the sample with h = 10 nm. The transition leads to an obvious strain delocalization, as clearly illustrated by the proposed theoretical model, which is based on the assumption of a pure shear stress state to quantify the shear banding-induced strain localization. The strain delocalization results from the higher density of amorphous/amorphous interfaces that exhibit the change in morphology with a refined layered glass structure.

Energy-efficient materials are key to combating the high energy costs and climate change. The manufacturing temperatures of industrially important Zr-based bulk metallic glasses (BMGs) relative to steels are low, and exist between the liquidus temperature Tl (∼850 °C) and glass transition temperature Tg (∼400 °C). However, these materials show limited plastic deformability (ductility) at room temperature (strains typically less than 3%); moreover they soften but exhibit limited ductility at high processing temperatures. Their low ductility should be improved because it impedes fatigue resistance and machinability, such as via cold (plastic) forming. In this study, chemical composition changes, which reduced Tg, resulted in remarkably ductile BMGs with extreme deformations of over 70% under compression, thereby enabling their energy-efficient processing at low temperatures. In contrast to previously reported conclusions on the high GFA and deformation-induced nanocrystallization being the precursors to ductility, formation of a low amount of meso-crystallites within the glassy material during cooling efficiently hindered the propagation of shear bands and microcracks under loading, thus increasing significantly ductility. This characteristic, in addition to optimal chemical composition, played an important role in improving the ability of BMGs to undergo solid-state processing at low temperatures and increased deformation rates.

The formation of flow-induced, oriented structures in two-phase systems, as in this study, is a phenomenon of considerable interest to the scientific and industrial sectors. The main difficulty in understanding the formation of bands of droplets is the simultaneous interplay of physicochemical, hydrodynamic, and mechanical effects. Additionally, banded structure materials frequently show multiple length scales covering several decades as a result of complex time-dependent stress fields. Here, to facilitate understanding a subset of these structures, we studied water in oil emulsions and focused on the effects of three variables specifically: the confinement factor (Co=2R/H), the viscosity ratio (p), and the applied shear rate (γ˙). The confinement (Co) is the ratio between the drop’s diameter (2R) and the separation of (the gap between) the circular rotating disks (H) containing the emulsion. We carried out (a) observations of the induced structure under different simple shear rates, as well as (b) statistical and morphological analysis of these bands. At low shear rates, the system self-assembles into bands along the direction of the flow and stacked normal to the velocity gradient direction. At higher shear rates is possible to observe bands normal to the vorticity direction. Here, we show that a detailed analysis of the dynamics of the band structures is amenable, as well as measurements of flow field anomalies simultaneously observed. The local emulsion viscosity varies in time, increasing in regions of higher droplet concentration and subsequently inducing velocity components perpendicular to the main flow direction. Thus, the emulsion morphology evolves and changes macroscopically. A relatively plausible explanation is attributed to the competitive effects of coalescence and the rupture of drops, where p values less than one predominate coalescence.

This article presents data regarding the research paper entitled “Hierarchically activated deformation mechanisms to form ultra-fine grain microstructure in carbon containing FeMnCoCr twinning induced plasticity high entropy alloy [1]”. In this article we provide supporting data for describing the associated mechanisms in microstructure evolution and grain refinement of a carbon-doped TWIP high-entropy alloy (HEA) during thermomechanical processing. Microstructural characterization before and after deformation was performed using scanning electron microscope (SEM) outfitted with EBSD detector and transmission electron microscopy (TEM) were used for microstructure observation and investigation of nanostructure evolution during deformation. Inverse pole figure (IPF) map, grain boundary map and kernel average misorientation map (KAM) were used for systematic analysis of nanostructural evolution and deformed heterostructure consisting of hierarchical mechanical twinning, shear-banding, microbanding and formation of strain-induced boundaries (SIBs).

Shear banding is an important deformation and failure mechanism in metallic systems, especially at high-rate straining. Dynamic recrystallization was often reported to account for the refined microstructure of shear bands but rarely confirmed using direct quantitative measurement. Here, we employ quantitative precession electron diffraction analysis to uncover shear band microstructure in pure titanium. The results reveal that the microstructure is dominated by early stages of grain subdivision process. Dynamic recrystallization is not as prevalent as perceived conventionally. Our results offer key insights into understanding shear banding and highlight the need for quantitative analyses of shear band microstructure.

Rheo-NMR velocimetry was used to study shear banding of a 6 wt.% cetylpyridinium chloride (CPCl) worm-like micelle solution under shear startup conditions with and without pre-shear. 1D velocity profiles across the fluid gap of a concentric cylinder Couette shear cell were measured every 1 s following shear startup for four different applied shear rates within the stress plateau. Fitting of the velocity profiles allowed calculation of the shear banding characteristics (shear rates in the high and low shear band, the interface position and apparent slip at the inner rotating wall) as the flow transitioned from transient to steady state regimes. Characteristic timescales to reach steady state were obtained and found to be similar for all shear banding characteristics. Timescales decreased with increasing applied shear rate. Large temporal fluctuations with time were also observed and Fourier transform of the time and velocity autocorrelation functions quantified the fluctuation frequencies. Frequencies corresponded to the elastically driven hydrodynamic instabilities, i.e. vortices, that are known to occur in the unstable high shear band and were dependent upon both applied shear rate and the pre-shear protocol.

We investigated the shear banding phenomena in the non-isothermal simple-shear flow of a viscoelastic-fluid-based nanofluid (VFBN) subject to exothermic reactions. The polymeric (viscoelastic) behavior of the VFBN was modeled via the Giesekus constitutive equation, with appropriate adjustments to incorporate both the non-isothermal and nanoparticle effects. Nahme-type laws were employed to describe the temperature dependence of the VFBN viscosities and relaxation times. The Arrhenius theory was used for the modeling and incorporation of exothermic reactions. The VFBN was modeled as a single-phase homogeneous-mixture and, hence, the effects of the nanoparticles were based on the volume fraction parameter. Efficient numerical schemes based on semi-implicit finite-difference-methods were employed in MATLAB for the computational solution of the governing systems of partial differential equations. The fundamental fluid-dynamical and thermodynamical phenomena, such as shear banding, thermal runaway, and heat transfer rate (HTR) enhancement, were explored under relevant conditions. Important novel results of industrial significance were observed and demonstrated. Firstly, under shear banding conditions of the Giesekus-type VFBN model, we observed remarkable HTR and Therm-C enhancement in the VFBN as compared to, say, NFBN. Specifically, the results demonstrate that the VFBN are less susceptible to thermal runaway than are NFBN. Additionally, the results illustrate that the reduced susceptibility of the Giesekus-type VFBN to the thermal runaway phenomena is further enhanced under shear banding conditions, in particular when the nanofluid becomes increasingly polymeric. Increased polymer viscosity is used as the most direct proxy for measuring the increase in the polymeric nature of the fluid.

Many fluids undergo shear banding, in which two states of different apparent viscosity coexist for a given shear rate (or for a given stress). In the idealized case of an infinite gap between shearing plates the selection of the conditions for shear banding has been shown to depend on the spatial structure and shape of the interface between shear bands. With the advent of microfluidic design for processing and additive manufacturing, the processing of many complex fluids often occurs in situations where this idealized limit doesn't apply, and the gap between walls, in either shearing flow or more often for pressure driven flow, is no longer “infinite” compared to the structural scales. It is increasingly clear that the effective rheology and structure of flowing fluids in these conditions requires information about the entire sample size, i.e., that the rheology is intrinsically non-local. In this review we discuss some recent attempts (both theoretical and experimental) to address non-local rheology and its implications for shear-banding flows of polymeric fluids. This manifests itself in rheology extracted from velocity profiles, as well as the dependence of shear-banding conditions on the position of the interface between shear bands, as well as the system size.

The case of a frictionless contact between a spherical body and a flat metallic glass is studied using a mesoscopic description of plasticity combined with a semi-analytical description of the elastic deformation in a contact geometry (code ISAAC). Plasticity is described by irreversible strain rearrangements in the maximum deviatoric strain direction, above some random strain threshold. In the absence of adhesion or friction, the plastic deformation is initiated below the surface. To represent the singularities due to adhesion, initial rearrangements are forced at the boundary of the contact. Then, the structural disorder is introduced in two different levels: either in the local strain thresholds for plasticity or in the residual plastic strains. It is shown that the spatial organization of plastic rearrangements is not universal, but it is very dependent on the choice of disorder and external loading conditions. Spatial curved shear bands may appear below the contact but only for a very specific set of parameters, especially those characterizing the random thresholds compared to externally induced strain gradients.

Measuring the rheological properties of multi-component (and multi-phase) systems meets with many special problems which are absent in flows of homogeneous materials. Such complex fluids have inherent structure and all the peculiarities of their behavior are determined by stress-induced temporal-spatial structure rearrangements. This paper is a review devoted to the physical origin and classification of problems encountered in the flow of multi-component materials. Stress-driven phenomena can be related to phase transformations (the formation of a new phase in polymerization, crystallization, amorphous phase separation), molecular and structure orientation, and various forms of self-organization. Some of these time effects are considered to be thixotropic phenomena. Thixotropy of multi-component matters leads to absence of an upper Newtonian plateau, time (rate)-dependence of yield stress and the layered flow in the range of high shear rates. The flow of such matters can lead to the formation of spatially divided structures with different properties and displacement of structures at the macroscopic level that excludes traditional measures of their rheological properties. In addition, the flow of multi-component systems is accompanied by the appearance of anisotropy of their properties. It is emphasized that the stressdriven evolution of rheological properties are not taken into account in the existing widely used constitutive equations.

This study investigates dilute aqueous suspensions of bentonite particles using magnetic resonance imaging (MRI) velocimetry. Four different chemical conditions are tested to investigate the influence of pH and type of monovalent electrolyte on the local rheological behavior of bentonite suspensions. The results indicate the shear banding in a dilute suspension of 0.1 vol.% solid due to the formation of a continuous three-dimensional particle network under a certain chemical environment (i.e., pH 4 in 1 × 10−2 M KNO3). This network is responsible for the existence of the yield stress in that dilute suspension. Structural changes induced by modification of suspensions’ chemistry are examined via scanning electron microscopy. A previously established method based on processing the torques acquired via conventional rheometric measurement is also applied as an alternative way to recover local flow information. Within the shear rate range covered by our MRI velocimetry, the results of both methods show good agreement. This study suggests that the existence of a master curve (or global flow curve) for dilute suspensions is dependent on the bentonite particle organization, which is influenced by the suspension chemistry and the previous flow history.

The transition from viscous to brittle behaviour in magmas plays a decisive role in determining the style of volcanic eruptions. While this transition has been determined for one- or two-phase systems, it remains poorly constrained for natural magmas containing silicic melt, crystals, and gas bubbles. Here we present new experimental results on shear-induced fracturing of three-phase magmas obtained at high-temperature (673-1023 K) and high-pressure (200 MPa) conditions over a wide range of strain-rates (5·10-6 s-1 to 4·10-3 s-1). During the experiments bubbles are deformed (i.e. capillary number are in excess of 1) enough to coalesce and generate a porous network that potentially leads to outgassing. A physical relationship is proposed that quantifies the critical stress required for magmas to fail as a function of both crystal (0.24 to 0.65) and bubble volume fractions (0.09 to 0.12). The presented results demonstrate efficient outgassing for low crystal fraction (< 0.44), whereas high crystal fractions (> 0.44) promote gas bubble entrapment and inhibit outgassing. The failure of bubble-free, crystal-bearing systems is enhanced by the presence of bubbles that lower the critical failure stress in a regime of efficient outgassing, while the failure stress is increased if bubbles remain trapped within the crystal framework. These contrasting behaviours have direct impact on the style of volcanic eruptions. During magma ascent, efficient outgassing reduces the potential for an explosive eruption and favours brittle behaviour, contributing to maintain low overpressures in an active volcanic system resulting in effusion or rheological flow blockage of magma at depth. Conversely, magmas with high crystallinity experience limited loss of exsolved gas, permitting the achievement of larger overpressures prior to a potential sudden transition to brittle behaviour, which could result in an explosive volcanic eruption.