A shear thickening-chemical polishing (ST-CP) approach exploiting the recombination mechanism of shear-thickening and chemical-physical friction is proposed for ultraprecision machining of optical ...materials. The ST-CP slurries with dynamic rheological behaviour are characterized, and the optimal preparation process is explored for high-efficiency polishing of workpieces. A critical shear rate (CSR) prediction model in the flow field of slurries is systematically investigated and experimentally verified in detail. A mathematical control of the material removal rate (MRR) is modelled and developed for ST-CP. The shear-thickening-induced micro-cutting and chemical-physical friction contribute to the material removal mechanism in the ST-CP process. A special chemical reaction layer consisting of Li2O and Nb2O7 evoked on the workpiece, which can soften the surface layer of lithium niobate (LiNbO3), increases the chemical-physical friction and material removal through micro-cutting and shearing. The material removal process in ST-CP is a dynamic equilibrium process in which atoms of the workpiece surface are continuously involved to form new substances or oxides to achieve a soft chemical reaction layer, accompanied by the shear-thickening-induced micro-cutting action. A series of ST-CP experiments validate that the maximal error between theoretical and experimental data is less than 11.5%, which shows the high degree of accuracy of the MRR prediction model. Measurements and calculations are performed to explore the effects of shearing velocities, Al2O3 content, pH value, and oxidant content on surface roughness and MRR. When the shear-thickening induced micro-cutting and chemical reaction reach a dynamic equilibrium, a maximum MRR of up to 65.8 mg/h is achieved, and surface roughness is significantly reduced within 120 min from Ra 36.04 nm–1.46 nm with low subsurface damage (<5 nm). This investigation reveals that ST-CP is a progressive ultra-precision manufacturing approach for optical polishing and finishing of crystal materials.
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•A shear thickening-chemical polishing (ST-CP) method is proposed for ultraprecision machining of optical materials.•Specific shear thickening-chemical polishing slurries (ST-CP slurries) are prepared for high-efficiency polishing of workpieces.•A critical shear rate (CSR) prediction model in the flow field of ST-CP slurries is systematically investigated and experimentally verified in detail.•A mathematical material removal rate (MRR) model is established to reveal the ST-CP machining mechanism.•ST-CP is a progressive ultraprecision manufacturing approach for optical polishing and finishing and an ultraprecision optical crystal with surface roughness of Ra 1.46 nm and low subsurface damage (<5 nm) can be achieved in ST-CP.
A multifunctional shear thickening gel (MSTG) with both shear thickening performance and magnetorheological effect was prepared by dispersing the carbonyl iron powder into shear stiffening polymer ...matrix. Upon varying the mass ratio of pyroboric acid to polydimethylsiloxane from 0 to 0.6, the relative shear thickening effect of MSTG first increases and then decreases, demonstrating an excellent shear thickening property between the ratio within 0.2–0.4. A molecular chain model of the cross-linked bond was proposed to illustrate the shear thickening mechanism, and verified by the impact test of MSTG with different proportions. It is believed that more cross-linked bonds were formed at a higher external impact velocity due to the stimuli-response performance of MSTG.
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•Variation rules of ST effect and chain model of MSTG were put forward.•The chain model was verified by the impact test of MSTG.•An optimization method was proposed to obtain higher shear thickening effect.•Energy dissipation values of MSTG at distinct impact velocities were simulated.
Surface roughness affects many properties of colloids, from depletion and capillary interactions to their dispersibility and use as emulsion stabilizers. It also impacts particle–particle frictional ...contacts, which have recently emerged as being responsible for the discontinuous shear thickening (DST) of dense suspensions. Tribological properties of these contacts have been rarely experimentally accessed, especially for nonspherical particles. Here, we systematically tackle the effect of nanoscale surface roughness by producing a library of all-silica, raspberry-like colloids and linking their rheology to their tribology. Rougher surfaces lead to a significant anticipation of DST onset, in terms of both shear rate and solid loading. Strikingly, they also eliminate continuous thickening. DST is here due to the interlocking of asperities, which we have identified as “stick–slip” frictional contacts by measuring the sliding of the same particles via lateral force microscopy (LFM). Direct measurements of particle–particle friction therefore highlight the value of an engineering-tribology approach to tuning the thickening of suspensions.
Shear thickening in dense particulate suspensions was recently proposed to be driven by the activation of friction above an onset stress needed to overcome repulsive forces between particles. Testing ...this scenario represents a major challenge because classical rheological approaches do not provide access to the frictional properties of suspensions. Here we adopt a different strategy inspired by pressure-imposed configurations in granular flows that specifically gives access to this information. By investigating the quasi-static avalanche angle, compaction, and dilatancy effects in different nonbuoyant suspensions flowing under gravity, we demonstrate that particles in shear-thickening suspensions are frictionless under low confining pressure. Moreover, we show that tuning the range of the repulsive force below the particle roughness suppresses the frictionless state and also the shear-thickening behavior of the suspension. These results, which link microscopic contact physics to the suspension macroscopic rheology, provide direct evidence that the recent frictional transition scenario applies in real suspensions.
3D printing of high‐strength and antiswelling hydrogel‐based load‐bearing soft tissue scaffolds with similar geometric shape to natural tissues remains a great challenge owing to insurmountable ...trade‐off between strength and printability. Herein, capitalizing on the concentration‐dependent H‐bonding‐strengthened mechanism of supramolecular poly(N‐acryloyl glycinamide) (PNAGA) hydrogel, a self‐thickening and self‐strengthening strategy, that is, loading the concentrated NAGA monomer into the thermoreversible low‐strength PNAGA hydrogel is proposed to directly 3D printing latently H‐bonding‐reinforced hydrogels. The low‐strength PNAGA serves to thicken the concentrated NAGA monomer, affording an appropriate viscosity for thermal‐assisted extrusion 3D printing of soft PNAGA hydrogels bearing NAGA monomer and initiator, which are further polymerized to eventually generate high‐strength and antiswelling hydrogels, due to the reconstruction of strong H‐bonding interactions from postcompensatory PNAGA. Diverse polymer hydrogels can be printed with self‐thickened corresponding monomer inks. Further, the self‐thickened high‐strength PNAGA hydrogel is printed into a meniscus, which is implanted in rabbit's knee as a substitute with in vivo outcome showing an appealing ability to efficiently alleviate the cartilage surface wear. The self‐thickening strategy is applicable to directly printing a variety of polymer‐hydrogel‐based tissue engineering scaffolds without sacrificing mechanical strength, thus circumventing problems of printing high‐strength hydrogels and facilitating their application scope.
A self‐thickening and self‐strengthening strategy is developed to directly 3D print supramolecular poly(N‐acryloyl glycinamide) (PNAGA) hydrogels, and extended to printing a wide variety of polymer hydrogels with an ability to maintain robust mechanical strengths. The high‐strength and antiswelling PNAGA hydrogel is printed into a meniscus scaffold that is implanted into the knees of rabbits, eventually efficiently protecting cartilage.
Sandwich composite panels (SCPs) with carbon fibre reinforced plastic (CFRP) facings are usually vulnerable to low-velocity transverse impact loading. In this study, a method is presented to improve ...the impact resistance and energy absorption capacity of CFRP-faced SCPs by filling them with a concentrated styrene/acrylate particle based shear thickening fluid (STF). First, for the STF alone, aspects of mechanical performance, namely rheological and low-velocity impact behaviours, were systematically examined. It was found that the critical shear stress of the STF was lower than that of silica particle based STF with a similar particle size and volume fraction, indicating that shear thickening was more easily achieved in the styrene/acrylate particle based STF. In addition, the STF exhibited much higher energy absorption capacity than an aluminium foam. Finally, low-velocity transverse impact experiments were performed on STF-filled SCPs with two core thicknesses, 7.2 mm and 12.7 mm. It was shown that the absorbed energy of the SCPs with a thin core increased by up to 99.3%, while the impact damage of SCPs with a thick core could be effectively suppressed on the back surface of the SCPs. The impact mechanism of the STF-filled SCPs is also discussed. This study provides a new method for the design of impact-resistant SCPs.
Particle-based simulations of discontinuous shear thickening (DST) and shear jamming (SJ) suspensions are used to study the role of stress-activated constraints, with an emphasis on resistance to ...gearlike rolling. Rolling friction decreases the volume fraction required for DST and SJ, in quantitative agreement with real-life suspensions with adhesive surface chemistries and "rough" particle shapes. It sets a distinct structure of the frictional force network compared to only sliding friction, and from a dynamical perspective leads to an increase in the velocity correlation length, in part responsible for the increased viscosity. The physics of rolling friction is thus a key element in achieving a comprehensive understanding of strongly shear-thickening materials.
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Dense particulate suspensions exhibit a dramatic increase in average viscosity above a critical, material-dependent shear stress. This thickening changes from continuous to discontinuous as the ...concentration is increased. Using direct measurements of spatially resolved surface stresses in the continuous thickening regime, we report the existence of clearly defined dynamic localized regions of substantially increased stress that appear intermittently at stresses above the critical stress. With increasing applied stress, these regions occupy an increasing fraction of the system, and the increase accounts quantitatively for the observed shear thickening. The regions represent high-viscosity fluid phases, with a size determined by the distance between the shearing surfaces and a viscosity that is nearly independent of shear rate but that increases rapidly with concentration. Thus, we find that continuous shear thickening arises from increasingly frequent localized discontinuous transitions between distinct fluid phases with widely differing viscosities.
ZnO rice like nonarchitects are grafted on the graphene carbon core via a rapid microwave synthesis route. The prepared grafted systems are characterized via XRD, SEM, RAMAN, and XPS to examined the ...structural and morphological parameters. Zinc oxide grafted graphene sheets (ZnO‐G) are further doped in β‐phase of polyvinylidene fluoride (PVDF) to prepare the polymer nanocomposites (PNCs) via mixed solvent approach (THF/DMF). β‐phase confirmation of PVDF PNCs is done by FTIR studies. It is observed that ZnO‐G filler enhances the β‐phase content in the PNCs. Non‐doped PVDF and PNCs are further studied for rheological behavior under the shear rate of 1–100 s−1. Doping of ZnO‐G dopant to the PVDF matrix changes its discontinuous shear thickening (DST) behavior to continues shear thickening behavior (CST). Hydrocluster formation and their interaction with the dopant could be the reason for this striking DST to CST behavioral change. Strain amplitude sweep (10−3% ‐10%) oscillatory test reveals that the PNCs shows extended linear viscoelastic region with high elastic modulus and lower viscous modulus. Effective shear thickening behavior and strong elastic strength of these PNCs present their candidature for various fields including mechanical and soft body armor applications.
A simple and rapid microwave synthesis technique has been explored in this work to graft ZnO on the graphene carbon core. Further, these grafted materials are doped in the PVDF to prepare nanocomposites. Prepared nanocomposites exhibit continuous shear thickening behaviour (CST), extended linear viscoelastic region (LVER), high elastic modulus and lower viscous modulus. These nanocomposites are best suited for mechanical and soft body armour applications.
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.
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