Single-phase shear thickening fluids (STFs) have been extensively investigated in body protective applications. However, researchers do not have long-standing past experience of multi-phase STFs in ...protection. In the present work, multi-phase STFs were fabricated adding different amount of silicon carbide (SiC) additives into silica and polyethylene glycol (PEG) based suspensions. The thickening rheology of multi-phase STFs was investigated through rheological measurements. Ballistic impacts on multi-phase STF treated fabrics were carried out using lead core bullets with the impact speed of ∼330 m/s. Based on the results, multi-phase STFs improve the ballistic performance of high performance fabrics in comparison to single-phase STFs however, the mass efficiency of fabrics has a loss of performance for high velocity impact conditions.
•Carbide additives disrupt the thickening behavior of Shear Thickening Fluids (STFs).•STF enhances the inter-yarn friction of fabric structures.•Carbide additives provide additional energy absorption mechanism for STF treated fabrics under ballistic impact.
A consensus has emerged that a constraint to rotational or sliding motion of particles in dense suspensions under flow is the genesis of the discontinuous shear thickening (DST) phenomenon. We show ...that tangential fluid lubrication interactions due to finite-sized asperities on particle surfaces effectively provide these constraints, changing the dynamics of particle motion. By explicitly resolving for the surface roughness of particles, we show that, while smooth particles exhibit continuous shear thickening, purely hydrodynamic interactions in rough particles result in DST. In contrast to the frictional contact model, the hydrodynamic model predicts negative first and second normal stress differences for dense suspensions in the shear thickened state.
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This work reported a novel conductive shear thickening gel-Kevlar fabrics (c-STG/Kevlar) body armor material which possessed both anti-impact performance and dynamic mechano-sensing behavior. Due to ...the excellent shear thickening effect, the c-STG/Kevlar showed a higher safeguarding property than the neat Kevlar. Under low-velocity drop tower loading, the maximum center force of c-STG/Kevlar was only 5768 N, which was nearly half of the neat Kevlar (11414 N). During the high-velocity ballistic testing, the monolayer c-STG/Kevlar sample could absorb 21.6% impact energy. The c-STG/Kevlar displayed a mechano-electric coupling character since the electrical resistance of the c-STG/Kevlar was linearly dependent on the external impacts. A possible sensing mechanism was proposed and it was found that the impact damages could be evaluated by the resistance variation. Finally, an in situ impact-sensing helmet was obtained by using c-STG/Kevlar, which indicated that the above smart fabrics had wide potential in next generation body armor materials and wearable devices.
An experimental investigation is conducted to study the influence of shear‐thickening behavior on the primary breakup process of suspension jets. The primary breakup morphologies of cornstarch–water ...suspension are observed via a high‐speed camera. The unique hardened breakup mode only occurs when the suspension exhibits discontinuous shear thickening (DST). During hardened breakup mode, the oscillating portion of the suspension jet becomes perpendicular to the air direction and keeps cylindrical instead of deforming into a thin sheet or membrane structure. The suspension jets break off into large pieces rather than tiny droplets. The dimensionless number N is established to describe the relative magnitude of the increment of the viscous force and aerodynamic force during the primary breakup process. The primary breakup regime map of Newtonian fluids and shear‐thickening suspensions is also promoted based on the dimensionless number N and the Weber number We.
Fine-particle suspensions (such as cornstarch mixed with water) exhibit dramatic changes in viscosity when sheared, producing fascinating behaviors that captivate children and rheologists alike. ...Examination of these mixtures in simple flow geometries suggests intergranular repulsion and its influence on the frictional nature of granular contacts is central to this effect—for mixtures at rest or shearing slowly, repulsion prevents frictional contacts from forming between particles, whereas when sheared more forcefully, granular stresses overcome the repulsion allowing particles to interact frictionally and form microscopic structures that resist flow. Previous constitutive studies of these mixtures have focused on particular cases, typically limited to 2D, steady, simple shearing flows. In this work, we introduce a predictive and general, 3D continuum model for this material, using mixture theory to couple the fluid and particle phases. Playing a central role in the model, we introduce a microstructural state variable, whose evolution is deduced from small-scale physical arguments and checked with existing data. Our space- and time-dependent model is implemented numerically in a variety of unsteady, nonuniform flow configurations where it is shown to accurately capture a variety of key behaviors: 1) the continuous shear-thickening (CST) and discontinuous shear-thickening (DST) behavior observed in steady flows, 2) the time-dependent propagation of “shear jamming fronts,” 3) the time-dependent propagation of “impactactivated jamming fronts,” and 4) the non-Newtonian, “running on oobleck” effect, wherein fast locomotors stay afloat while slow ones sink.
A magnetorheological shear thickening fluid (MSTF) is prepared through adding carbonyl iron particles and Al
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abrasives into the traditional shear thickening fluid (STF) to improve low shear ...stress characteristic of STF in this work. To select the optimal sample as base fluid for MSTF, a series of STFs was pre-prepared and its rheological characteristics were further tested, which contained different concentrations of starch polymer and abrasive. Furthermore, different character parameters of MSTFs, such as magnetic field intensity and carbonyl iron particle’s concentration, were experimentally tested to explore its rheological characteristics. Then, the magnetorheological effect on shear thickening formation of MSTFs was furtherly discussed. Experimental results show that with the same base fluid the viscosity and the shear stress of MSTFs are both higher than of STFs under the action of magnetic field. Moreover, the MSTF exhibits a good shear thickening effect under the weak magnetic field intensity and at low level of iron particle concentration, because the existence of hydrogen bonds and magnetic particle chains makes the shear thickening effect of MSTF enhanced by particle clusters. The results indicate that the MSTFs as polishing fluid contribute to develop a higher efficiency polishing method in the future.
•The solubility and thickening properties of polysiloxane modified by three different functional groups in supercritical CO2 were studied.•Vinyl polysiloxane has the best solubility and thickening ...capacity.•The thickening effect of vinyl polysiloxane in supercritical CO2 is affected by its kinematic viscosity and concentration.•The higher the kinematic viscosity and concentration of vinyl polysiloxane, the better the thickening ability.•Vinyl polysiloxane has the strongest molecular interaction with CO2, and this strong force is electrostatic.
Supercritical CO2 has been widely concerned because of its clean environmental protection and excellent performance. However, the low viscosity limits its wide application. To this issue, researchers usually use thickeners to improve its viscosity. The siloxane-type polymer is regarded as clean and cheap thickener. In this work, we screened potential supercritical CO2 thickeners by comparing the thickening properties of vinyl polysiloxane, hydroxyl polysiloxane and polydimethylsiloxane. The results show that vinyl polysiloxane has the best thickening performance. The dissolution and thickening behavior of vinyl polysiloxane are further studied. The results indicate that the dissolution pressure and thickening capacity of vinyl polysiloxane in supercritical CO2 increase with the increase of kinematic viscosity and concentration. At the experimental conditions, the maximum viscosity of supercritical CO2 can be increased to 14.87 mPa·s. In addition, the dissolution pressure of vinyl polysiloxane in supercritical CO2 decreases with the increase of cosolvent concentration, while the viscosity slightly decreases. Finally, the thickening mechanism of these thickeners was studied by molecular dynamics simulation. Based on the molecular simulation results, the roles of functional groups of thickeners in the dissolution and thickening process are discussed. It can provide theoretical support for the synthesis and screening of CO2 thickeners in the future.
We report experimental and computational observations of dynamic contact networks for colloidal suspensions undergoing shear thickening. The dense suspensions are comprised of sterically stabilized ...poly(methyl methacrylate) colloids that are spherically symmetric and have varied surface roughness. Confocal rheometry and dissipative particle dynamics simulations show that the shear thickening strength β scales exponentially with the scaled deficit contact number and the scaled jamming distance. Rough colloids, which experience additional rotational constraints, require an average of 1.5–2 fewer particle contacts as compared to smooth colloids, in order to generate the same β . This is because the surface roughness enhances geometric friction in such a way that the rough colloids do not experience a large change in the free volume near the jamming point. The available free volume for colloids of different roughness is related to the deficiency from the maximum number of nearest neighbors at jamming under shear. Our results further suggest that the force per contact is different for particles with different morphologies.
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We present a systematic rheological study on the fumed silica suspensions to understand the effect of particle and fluid parameters on the critical shear rate and shear thickening ratio. It was ...observed that removal of air bubbles and water contamination is crucial to prepare good shear thickening fluids. A careful sample preparation method was adopted to properly disperse the fumed silica particles in polyethylene glycol solution, and we achieved discontinuous shear thickening at low particle concentration. It was observed that the critical shear rate in shear thickening suspension is strongly influenced by both carrier fluid and particle concentration. However, the shear thickening ratio is mainly influenced by the particle parameters and the frictional forces between the particles. Increasing the amount of smaller particles in the suspension significantly decreases the maximum viscosity and shifts the onset of shear thickening to higher values of critical shear rates with much smaller shear thickening ratio. Further, a possible mechanism has been proposed based on the influence of carrier fluid and particle size distribution to explain the rheological behaviour of shear thickening suspension. Our study supports the theory of particle-particle frictional contacts as the main reason for the discontinuous shear thickening.
This paper presents a study of a novel nonlinear damper on vibration control of rotor system with variable damping by using a smart material- shear thickening fluid (STF), whose viscosity and damping ...will dramatically increase with shear rate. A STF damper was self-developed and dynamic model of the STF damper-rotor system was established by using the Bouc-Wen model as mechanical model of the smart material damper. The incremental harmonic balance (IHB) method combined with the arc-length method was presented to investigate the dynamic response of rotor system with hysteresis nonlinear damping force theoretically. Experimental study of STF damper on suppressing vibration of rotor system was carried out by using a Bently rotor test rig with two STF dampers. The damping effect under different damper installation direction, vibration frequency and amplitude were investigated theoretically and experimentally. Study shows that the nonlinear damper exhibits larger damping force and fuller hysteresis characteristics, so it has better effect on resonance energy absorption compared with the traditional linear damper; and its output damping force can increase dramatically with the change of frequency and amplitude. It is verified that the unbalance vibration, especially the resonance amplitude of rotor system can be effectively suppressed by nonlinear damping of STF damper. The study shows the feasibility and advantages of using the STF damper for potential applications of adaptive or semi-active vibration control of rotating machinery.
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