Shear Jamming Research Articles

Effect of Liquid Properties on the Non-Newtonian Rheology of Concentrated Silica Suspensions: Discontinuous Shear Thickening, Shear Jamming, and Shock Absorbance.

Concentrated particle suspensions exhibit rheological behavior, such as discontinuous shear thickening (DST) and dynamic shear jamming (SJ), which affect applications such as soft armors. Although the origin of this behavior in shear-activated particle-particle interactions has been identified, the effect of chemical factors, especially the role of liquids, on this behavior remains unexplored. Hydrogen bonding in suspensions has been proposed to be essential for frictional contacts between particles, and therefore, most studies on DST and SJ have focused on aqueous and protic organic media with a definite hydrogen bonding ability. To identify an alternative molecular mechanism, this study explored the effects of liquid polarity and an aprotic nature on the rheological behavior of concentrated suspensions of silica microparticles. Owing to their excellent particle dispersion, the DST behavior of polar liquids was observed, independent of protic and aprotic liquids. In contrast, nonpolar liquids formed particle agglomerates because of the particle-particle attraction and became a paste at a high particle fraction. The SJ behavior was confirmed for three aprotic organic liquids (propylene carbonate, 1,3-dimethyl-2-imidazolidinone, and 1,3-dimethylpropyleneurea), suggesting the hydrogen bonding ability of these aprotic liquids. The diverse mechanisms of shear-activated interactions between particles present material design possibilities for the non-Newtonian rheology of concentrated particle suspensions.

Jamming Memory into Acoustically Trained Dense Suspensions under Shear

Systems driven far from equilibrium often retain structural memories of their processing history. This memory has, in some cases, been shown to dramatically alter the material response. For example, work hardening in crystalline metals can alter the hardness, yield strength, and tensile strength to prevent catastrophic failure. Whether memory of processing history can be similarly exploited in flowing systems, where significantly larger changes in structure should be possible, remains poorly understood. Here, we demonstrate a promising route to embedding such useful memories. We build on work showing that exposing a sheared dense suspension to acoustic perturbations of different power allows for dramatically tuning the sheared suspension viscosity and underlying structure. We find that, for sufficiently dense suspensions, upon removing the acoustic perturbations, the suspension shear jams with shear stress contributions from the maximum compressive and maximum extensive axes that reflect or “remember” the acoustic training. Because the contributions from these two orthogonal axes to the total shear stress are antagonistic, it is possible to tune the resulting suspension response in surprising ways. For example, we show that differently trained sheared suspensions exhibit (1) different susceptibility to the same acoustic perturbation, (2) orders of magnitude changes in their instantaneous viscosities upon shear reversal, and (3) even a shear stress that increases in magnitude upon shear cessation. We work through these examples to explain the underlying mechanisms governing each behavior. Then, to illustrate the power of this approach for controlling suspension properties, we demonstrate that flowing states well below the shear jamming threshold can be shear jammed via acoustic training. Collectively, our work paves the way for using acoustically induced memory in dense suspensions to generate rapidly and widely tunable materials. Published by the American Physical Society 2024

Shear thickening and hysteresis in dense suspensions: The effect of particle shape

The flow of dense suspension of non-Brownian particles has been considered by various studies affected by their significance in a variety of industries and natural phenomena. In this study, we investigate the effect of polyhedron morphology on shear thickening, shear jamming, and hysteresis characteristics of non-Brownian suspension of acrylate particles. Particles with the same chemical nature and three different shapes of spherical (aspect ratio Γ = 1), elliptical paraboloid (Γ ≈ 1), and boat-shaped (Γ ≈ 3) are fabricated via photopolymerization-based methods. Studied suspensions show the shear-thinning behavior at low shear stresses and shear thickening behavior at the higher range of shear stress. Also, the strength of observed shear thickening is enhanced for the suspensions of polyhedron particles, which can be attributed to the heightened degree of interparticle frictional contacts. Furthermore, it is found that angularity not only shifts the predicted frictionless and frictional jamming packing fractions to lower values but also expands the shear jamming packing fraction range. Finally, a history-dependent hysteresis is observed in all samples due to the different particle spatial structures forming in ascending and descending flow modes. The observed hysteresis loops strongly depend on the volume fraction and diminish near the jamming packing fraction due to the restricted mobility space of particles. In addition, the tumbling of elongated particles also can decrease the hysteresis loop by enhancing viscosity in the ascending flow mode, where the structures are not fully developed.

Fracture and relaxation in dense cornstarch suspensions.

Dense suspensions exhibit the remarkable ability to switch dynamically and reversibly from a fluid-like to a solid-like, shear-jammed (SJ) state. Here, we show how this transition has important implications for the propensity for forming fractures. We inject air into bulk dense cornstarch suspensions and visualize the air invasion into the opaque material using time-resolved X-ray radiography. For suspensions with cornstarch mass fractions high enough to exhibit discontinuous shear thickening and shear jamming, we show that air injection leads to fractures in the material. For high mass fractions, these fractures grow quasistatically as rough cavities with fractured interfaces. For lower mass fractions, remarkably, the fractures can relax to smooth bubbles that then rise under buoyancy. We show that the onset of the relaxation occurs as the shear rate induced by the air cavity growth decreases below the critical shear rate denoting the onset of discontinuous shear thickening, which reveals a structural signature of the SJ state.

Dynamic simulation of powder spreading processes toward the fabrication of metal-matrix diamond composites in selective laser melting

A novel method for the integrated production of structural and functional metal-matrix diamond composites is provided by selective laser melting (SLM) in the field of diamond tools. However, the uneven distribution of diamond particles and loose packing density in the powder bed can easily result in poor performance of diamond tools. In this work, a discrete element method model of diamond/CuSn composite powders is developed to simulate blade-spreading processes. It investigates how powder bed quality and particle dynamics are affected by diamond powder physical properties and powder spreading process parameters. The findings reveal that coarse diamond particles exhibit strong force chains at low velocities, whereas contact force chains are weak for fine CuSn particles at high velocities. It shows that diamond particles with irregular shapes have poor diffusivity and spreadability due to the large friction and mechanical locking forces, which causes diamond particles segregation. Therefore, the packing density and uniformity of the powder bed are both improved by reducing the volume fraction and particle size of diamond particles. In addition, the powder bed quality is improved by increasing the powder layer thickness and decreasing the translational speed of the blade, which weakens the shear expansion and jamming of diamond particles. The results have some significance for optimizing powder spreading processes toward the production of metal-matrix diamond composites in SLM.

Universal scaling of shear thickening transitions

Nearly, all dense suspensions undergo dramatic and abrupt thickening transitions in their flow behavior when sheared at high stresses. Such transitions occur when the dominant interactions between the suspended particles shift from hydrodynamic to frictional. Here, we interpret abrupt shear thickening as a precursor to a rigidity transition and give a complete theory of the viscosity in terms of a universal crossover scaling function from the frictionless jamming point to a rigidity transition associated with friction, anisotropy, and shear. Strikingly, we find experimentally that for two different systems—cornstarch in glycerol and silica spheres in glycerol—the viscosity can be collapsed onto a single universal curve over a wide range of stresses and volume fractions. The collapse reveals two separate scaling regimes due to a crossover between frictionless isotropic jamming and frictional shear jamming, with different critical exponents. The material-specific behavior due to the microscale particle interactions is incorporated into a scaling variable governing the proximity to shear jamming, that depends on both stress and volume fraction. This reformulation opens the door to importing the vast theoretical machinery developed to understand equilibrium critical phenomena to elucidate fundamental physical aspects of the shear thickening transition.

Numerical simulation of shear jamming in a shear thickening fluid under impact

Numerical simulation of shear jamming in a shear thickening fluid under impact

Leveraging the Polymer Glass Transition to Access Thermally Switchable Shear Jamming Suspensions.

Suspensions of polymeric nano- and microparticles are fascinating stress-responsive material systems that, depending on their composition, can display a diverse range of flow properties under shear, such as drastic thinning, thickening, and even jamming (reversible solidification driven by shear). However, investigations to date have almost exclusively focused on nonresponsive particles, which do not allow in situ tuning of the flow properties. Polymeric materials possess rich phase transitions that can be directly tuned by their chemical structures, which has enabled researchers to engineer versatile adaptive materials that can respond to targeted external stimuli. Reported herein are suspensions of (readily prepared) micrometer-sized polymeric particles with accessible glass transition temperatures (T g) designed to thermally control their non-Newtonian rheology. The underlying mechanical stiffness and interparticle friction between particles change dramatically near T g. Capitalizing on these properties, it is shown that, in contrast to conventional systems, a dramatic and nonmonotonic change in shear thickening occurs as the suspensions transition through the particles' T g. This straightforward strategy enables the in situ turning on (or off) of the system's ability to shear jam by varying the temperature relative to T g and lays the groundwork for other types of stimuli-responsive jamming systems through polymer chemistry.

Using high-speed ultrasound to visualize dynamic jamming of dense suspensions

A remarkable property of concentrated, or dense, suspensions comprising nanometer- to micrometer-size particles in a liquid is their ability to transform from a liquid-like to a solid-like state under applied stress. This jamming phenomenon can be triggered by impact at the surface of a dense suspension and generates a shear front that propagates into the bulk of the material. Tracking and visualizing such front is difficult because suspensions are typically opaque optically, and the front can propagate at several meters per second. This talk will discuss high-speed ultrasound imaging (10 000 frames per second) to extract the flow field associated with the front propagation and visualize the associated shear jamming process. Unlike densification in dry granular media, jamming by shear does not involve significant changes in the local particle fraction while driving the transition to solid-like behavior. On the basis of these findings, we discuss ideas that link the transient stress response of dense suspensions to current theoretical models, which almost exclusively focus on steady-state shearing conditions.

Capillary-Stress Controlled Rheometer Reveals the Dual Rheology of Shear-Thickening Suspensions

The rheology of dense colloidal suspensions, which may undergo discontinuous shear thickening or shear jamming, is particularly difficult to analyze with conventional rheometers. Here, we develop a rheometer adapted to colloidal suspensions: the “capillarytron,” which uses the air-suspension capillary interface to impose particle (or osmotic) pressure during shear. The main virtues of this new device are that (i) it gives direct access to the suspension friction coefficient, (ii) it operates for very dense suspensions up to jamming, and, most importantly, (iii) it decouples the stresses developed within the suspension from the applied shear rate. We can, thus, smoothly move through the different frictional states of the system, precisely in the range of volume fractions where discontinuous shear thickening or shear jamming occur under volume-imposed conditions. Our results obtained with the capillarytron provide the first complete characterization of the dual frictional behavior of a model shear-thickening suspension, in agreement with the recently proposed frictional transition scenario. Based on a new concept in rheometry, the capillarytron unlocks the path to pressure-imposed rheology on colloidal and Brownian suspensions. Moreover, its fine control of the particle pressure via the soft capillary interface opens the possibility to explore the flow of “fragile” particles close to jamming, such as Brownian colloids, active particles, and living cells.Received 18 November 2022Revised 15 December 2022Accepted 9 January 2023DOI:https://doi.org/10.1103/PhysRevX.13.011024Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasJammingNon-Newtonian fluidsRheologyPhysical SystemsComplex fluidsGranular fluidsPolymers & Soft Matter

Discontinuous rigidity transition associated with shear jamming in granular simulations.

We investigate the rigidity transition associated with shear jamming in frictionless, as well as frictional, disk packings in the quasi-static regime and at low shear rates. For frictionless disks, the transition under quasi-static shear is discontinuous, with an instantaneous emergence of a system spanning rigid clusters at the jamming transition. For frictional systems, the transition appears continuous for finite shear rates, but becomes sharper for lower shear rates. In the quasi-static limit, it is discontinuous as in the frictionless case. Thus, our results show that the rigidity transition associated with shear jamming is discontinuous, as demonstrated in the past for isotropic jamming of frictionless particles, and therefore a unifying feature of the jamming transition in general.

Amplitude-dependent rheological responses of axisymmetric grains

Oscillatory shear flows of axisymmetric grains exhibit amplitude-dependent rheological responses, which is related to the evolution of the microstructure. In this work, it is shown that the highly ordered configuration of grains at steady-state shear flow undergoes microstructural rearrangement when subjected to shear oscillations. This rearrangement may lead to reduced ordering configurations which give rise to macroscale shear hardening, which can result in shear jamming if the applied shear traction is below the critical shear resistance. On the other hand, it was observed that applying oscillatory shear to the primary condensed shear flow enhances flowability due to microstructure rearrangement. In this study, we investigate the amplitude-dependent rheological responses of axisymmetric grains subjected oscillatory shear flows. First, we look into the evolution of grains alignment subjected to a range of oscillation amplitudes, where we show that the lower oscillation amplitudes have the potential to change the orientation from the ordered steady state to a completely disordered (isotropic) orientation. Next, we study the dependency of the shear flow resistance on the microstructure configuration, and show that the strain hardening and potential jamming have strong dependency on the oscillations amplitude. We also show that, in the case of jamming, the shear strain and the corresponding number of oscillation cycles depend not only on the grains aspect ratio but also on the oscillation amplitude.

Role of confinement in the shear banding and shear jamming in noncolloidal fiber suspensions.

The jamming effect is critical in processing short fiber-reinforced thermoplastics (FRTs). Fiber jamming can induce discontinuous shear thickening (DST) in simple shear and result in fiber-matrix separation in more complex flows such as injection molding and compression molding of FRTs. The confinement effect commonly induces local jams and strongly enhances fiber jamming. However, the transient evolution of local fiber jams under confinement and its correlation with the tumbling of fibers are still elusive. In this study, we adopted rheo-PIV (particle image velocity) techniques to study this effect for glass fiber-reinforced thermoplastics (FRTs). The translational and tumbling motion of fiber were determined during rheological measurements, and the distribution of fiber orientation was determined by X-ray CT. Three shear banding regions appeared after the viscosity overshoot under high shear stress in suspensions with high fiber content, which was associated with the three regions of fiber orientation across the gap due to confinement. Shear banding was ascribed to the different tumbling speeds across the gap because of the different initial orientations and different wall confinements near and far from the wall. The local shear thickening and jamming behavior became most significant under intermediate confinement, and were affected by shear strain, shear stress, and fiber contents. 3D state diagrams were constructed to show the confinement effect on the evolution of shear banding and jamming.

Copper phosphate nanosheets as high-performance oil-based nanoadditives: Tribological properties and lubrication mechanism

Geometric variables and surface chemistry of nanomaterials as lubricant additives both affect the details on the interacting frictional surface. Herein, copper phosphate nanosheets (CPNs) were synthesized by a simple and facile method, which exhibited extraordinary tribological properties as the novel lubricating oil nanoadditives. Compared with the base oil, the friction coefficient (COF) has been reduced by 77% by CPNs at a concentration of 20 wt%, which could also protect the titanium alloy surface from any measurable wear. But as the CPNs content increased to 25 wt%, the shear jamming caused by hydrogen bonding between crystal water in CPNs may interfere with lubrication. Besides, it is significantly effective in preventing the adhesions of titanium alloy on the surface of counterface at a suitable concentration. The extraordinary tribological performance is contributed to the nanosheets of copper phosphate but not the nanoparticles. Moreover, in the presence of CPNs, the tribo-film containing CPNs is formed during sliding contact, but this tribo-film can’t hold for a long time without CPNs, indicating that CPNs can well retain the tribo-film. However, the dominant factor for friction reduction and antiwear is not this tribo-film but the solid-liquid interface lubrication between nanosheets and lubricating oil. The Stribeck curves were used to explain how CPNs play a role in boundary lubrication and mixed lubrication.

Coexistence of solid and liquid phases in shear jammed colloidal drops

Complex fluids exhibit a variety of exotic flow behaviours under high stresses, such as shear thickening and shear jamming. Rheology is a powerful tool to characterise these flow behaviours over the bulk of the fluid. However, this technique is limited in its ability to probe fluid behaviour in a spatially resolved way. Here, we utilise high-speed imaging and the free-surface geometry in drop impact to study the flow of colloidal suspensions. Here, we report observations of coexisting solid and liquid phases due to shear jamming caused by impact. In addition to observing Newtonian-like spreading and bulk shear jamming, we observe the transition between these regimes in the form of localised patches of jammed suspension in the spreading drop. We capture shear jamming as it occurs via a solidification front travelling from the impact point, and show that the speed of this front is set by how far the impact conditions are beyond the shear thickening transition.

A study of dense suspensions climbing against gravity

Dense suspensions have previously been shown to produce a range of anomalous and gravity-defying behaviors when subjected to strong vibrations in the direction of gravity. These behaviors have previously been interpreted via analogies to inverted pendulums and ratchets, language that implies an emergent solid-like structure within the fluid. It is therefore tempting to link these flow instabilities to shear jamming (SJ), but this is too restrictive since the instabilities can also be observed in systems that shear thicken but do not shear jam. As an alternative perspective, we re-frame earlier ideas about “racheting” as a “negative viscosity” effect, in which the cycle-averaged motion of a vibrated fluid is oriented opposite to the direction implied by the cycle-averaged stresses. Using ideas from the Wyart and Cates modeling framework, we predict that such a “negative viscosity” can be achieved in shear flows driven by oscillating stress with both square and sinusoidal wave forms. We extend this same modeling approach to study falling films in a vibrating gravitational field, where we similarly find it is possible to attain an overall flow opposite the direction of gravity. Preliminary experimental findings are also provided in support of the modeling work. • Vertically vibrated dense suspensions can climb against gravity. • We explain this phenomena in terms of an “effective” negative viscosity. • Mechanism is explored in detail using simple modeling tools. • Preliminary experiments reveal climbing on vertically oriented surfaces. • Experimental observations are consistent with model predictions.

Granulation and suspension rheology: A unified treatment

Mixing a small amount of liquid into a powder can give rise to dry-looking granules; increasing the amount of liquid eventually produces a flowing suspension. We perform experiments on these phenomena using Spheriglass, an industrially realistic model powder. Drawing on recent advances in understanding friction-induced shear thickening and jamming in suspensions, we offer a unified description of granulation and suspension rheology. A “liquid incorporation phase diagram” explains the existence of permanent and transient granules and the increase of granule size with liquid content. Our results point to rheology-based design principles for industrial granulation.

Ultrastable Shear-Jammed Granular Material

Dry granular materials, such as sand, gravel, pills, or agricultural grains, can become rigid when compressed or sheared. Under isotropic compression, the material reaches a certain jamming density and then resists further compression. Shear jamming occurs when resistance to shear emerges in a system at a density lower than the jamming density. Although shear jamming is prevalent in frictional granular materials, their stability properties are not well described by standard elasticity theory and thus call for experimental characterization. We report on experimental observations of changes in the mechanical properties of a shear-jammed granular material subjected to small-amplitude, quasistatic cyclic shear. We study a layer of plastic disks confined to a shear cell, using photoelasticimetry to measure all interparticle vector forces. For sufficiently small cyclic shear amplitudes and large enough initial shear, the material evolves to an unexpected “ultrastable” state in which all the particle positions and interparticle contact forces remain unchanged after each complete shear cycle for thousands of cycles. The stress response of these states to small imposed shear is nearly elastic, in contrast to the original shear-jammed state.5 MoreReceived 14 January 2022Revised 18 May 2022Accepted 8 July 2022DOI:https://doi.org/10.1103/PhysRevX.12.031021Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective behaviorDynamical phase transitionsElasticityFatigueGranular materialsJammingMechanical deformationRheologyStatistical PhysicsInterdisciplinary PhysicsCondensed Matter, Materials & Applied PhysicsNetworksPolymers & Soft Matter

In Situ Observation of Shear-Induced Jamming Front Propagation during Low-Velocity Impact in Polypropylene Glycol/Fumed Silica Shear Thickening Fluids.

Shear jamming, a relatively new type of phase transition from discontinuous shear thickening into a solid-like state driven by shear in dense suspensions, has been shown to originate from frictional interactions between particles. However, not all dense suspensions shear jam. Dense fumed silica colloidal systems have wide applications in the industry of smart materials from body armor to dynamic dampers due to extremely low bulk density and high colloid stability. In this paper, we provide new evidence of shear jamming in polypropylene glycol/fumed silica suspensions using optical in situ speed recording during low-velocity impact and explain how it contributes to impact absorption. Flow rheology confirmed the presence of discontinuous shear thickening at all studied concentrations. Calculations of the flow during impact reveal that front propagation speed is 3–5 times higher than the speed of the impactor rod, which rules out jamming by densification, showing that the cause of the drastic impact absorption is the shear jamming. The main impact absorption begins when the jamming front reaches the boundary, creating a solid-like plug under the rod that confronts its movement. These results provide important insights into the impact absorption mechanism in fumed silica suspensions with a focus on shear jamming.

Origin of Two Distinct Stress Relaxation Regimes in Shear Jammed Dense Suspensions.

Many dense particulate suspensions show a stress induced transformation from a liquidlike state to a solidlike shear jammed (SJ) state. However, the underlying particle-scale dynamics leading to such striking, reversible transition of the bulk remains unknown. Here, we study transient stress relaxation behaviour of SJ states formed by a well-characterized dense suspension under a step strain perturbation. We observe a strongly nonexponential relaxation that develops a sharp discontinuous stress drop at short time for high enough peak-stress values. High resolution boundary imaging and normal stress measurements confirm that such stress discontinuity originates from the localized plastic events, whereas system spanning dilation controls the slower relaxation process. We also find an intriguing correlation between the nature of transient relaxation and the steady-state shear jamming phase diagram obtained from the Wyart-Cates model.