Analysis of Uniform Film Thickness and Stationarypoints for the Thin Film Flow of Carreau Fluid Model in the Presence of Surface Tension Gradient

This article addresses the analysis of the uniform film thickness and stationary points forthe Carreau thin fluid film flow. The flow of fluid on a vertically upward moving cylinder takesplace in the presence of a surface tension gradient. The resulting non-linear and inhomogeneousordinary differential equation is solved for the series form solution using Adomian decompositionmethods (ADM). Stokes number St, inverse capillary number C, Weissenberg number W e andfluid behavior index n emerged as flow control parameters. The analysis showed that thepositions of stationary points transferred towards the surface of the cylinder by the increase ofSt and C while towards the fluid-air interface by the increase of n. W e delineated vice versaeffects on positions of stationary points for the shear thickening fluid film and shear thinningfluid film. The width of uniform film thickness reduces by an increment in the St and Cwhereas it increases by an increment in the n. The width of shear thickening uniform filmthickness increases whilst shear thinning uniform film thickness decreases as the W e increases. A comparison between the linearly viscous fluid and Carreau fluid is also made.

Bioink Rheology Regulates Stability of Bioprinted Strands

Extrusion three-dimensional (3D) bioprinting typically requires an ad-hoc trial-and-error optimization of the bioink composition towards enhanced resolution. The bioink solutions are solidified after leaving cone-shaped or cylindrical nozzles. The presence of bioink instability not only hampers the extrusion resolution but also affects the behavior of embedded cellular components. This is a key factor in selecting bioinks and bioprinting design parameters for well-established desktop and handheld bioprinters. In this work, we developed an analytical solution for the process of bioink deposition and compared its predictions against numerical simulations of the deposition. We estimated the onset of bioink instability as a function of bioink rheological properties and nozzle geometry. Both analytical and simulation results demonstrated that enhancing shear-thinning behavior of the bioink stabilizes the printing process whereas bioink shear-thickening behavior induces an opposite effect through extending the toe region of the deposition. The present study serves as a benchmark for detailed simulations of the extrusion process for optimal bioprinting.

Static puncture resistance characteristics with various indenter nose shape geometry perforation of shear thickening fluid impregnated polypropylene fabric for soft armour application

At present, puncture resistance and rheological performance of shear thickening fluid (STF) is an essential design requirement for a soft armour material (target sample). The target sample is prepared with a dip and dry process of STF impregnated woven polypropylene (PP) fabric. These samples were tested and compared with neat PP fabric. The penetration depth of target samples is highly sensitive to the coefficient of friction between the indenter’s nose shape geometry and the target sample. The STF is prepared by mechanical dispersion of synthesized microsphere silica microparticles at a volume fraction of 57% in polyethylene glycol (400 g/mol). The rheological response indicates that the prepared concentration of silica microparticles in the STF suspension is observed to have a better shear thickening effect. The viscosity of suspension is highly sensitive to silica aspect ratio, volume fraction and particle size distribution in this work. Tensile tests along with puncture resistance with different indenter nose shapes geometry (hemispherical, elliptical, flat and conical) have been performed in the present study. Results indicate that the energy absorption is more with the hemispherical indenter and less with that of the conical indenter, which is attributed to the minimum surface area of contact as compared to all other indenters. A total of 16 number of fabricated target samples with various coating thicknesses of STF impregnated fabrics achieved the desired tensile strength, modulus and puncture resistance.

A phenomenological theory-based viscosity model for shear thickening fluids

A viscosity model for shear thickening fluids (STFs) based on phenomenological theory is proposed. The model considers three characteristic regions of the typical material properties of STFs: a shear thinning region at low shear rates, followed by a sharp increase in viscosity above the critical shear rate, and subsequently a significant failure region at high shear rates. The typical S-shaped characteristic of the STF viscosity curve is represented using the logistic function, and suitable constraints are applied to satisfy the continuity of the viscosity model. Then, the Levenberg–Marquardt algorithm is introduced to fit the constitutive model parameters based on experimental data. Verification against experimental data shows that the model can predict the viscosity behavior of STF systems composed of different materials with different mass concentrations and temperatures. The proposed viscosity model provides a calculation basis for the engineering applications of STFs (e.g., in increasing impact resistance and reducing vibration).

Rheological Properties of Magnetic Field-Assisted Thickening Fluid and High Efficiency Spherical Polishing of ZrO2 Ceramics

Shear thickening polishing technology using non-Newtonian polishing fluid is a low-cost, low-damage polishing method for the ultra-precision machining of complex curved surfaces. However, the shortcomings of traditional shear thickening polishing fluid in polishing efficiency and fluid viscosity controllability limit its further application., a novel weak magnetic field-assisted shear thickening polishing fluid (WMFA-STPF) containing carbonyl iron particles (CIPs) is presented in this study, which utilizes its weak magnetorheological effect to strengthen the shear thickening phenomenon. The rheological characteristics of the WMFA-STPF samples were investigated. The results show that WMFA-STPF has good fluidity in the low shear rate range and better thickening characteristics in the working shear rate range. In order to verify the high efficiency, high quality and high uniformity polishing ability of the weak magnetic field-assisted shear thickening polishing technology for the spherical surface of zirconia ceramic workpiece, the contrast polishing experiment was designed and finished. The experimental results show that the weak magnetic field-assisted thickening effect can achieve high efficiency and high quality polishing of hard and brittle ceramics. After 75 min polishing, the surface damage was effectively improved and eliminated, the surface quality and uniformity were greatly improved, and the material removal rate reached 7.82 μm/h, increased by 156%.

Effects of shear-thickening polymer on force attenuation capacities in hip protectors

Many elderly people use hip protectors to prevent hip fractures from sideways falls. These hip protectors absorb or shunt away the energy applied to the greater trochanter. Herein, shear-thickening polymer (STP)-based hip protectors composed of STP and polyurethane foam are studied. The purpose of this study was to identify the main factor that reduces the impact force directly applied to the femoral neck region and to determine the optimal thickness of STP in hip protectors. Seven hip protectors of different thicknesses were prepared, and two sets of free-fall mechanical tests with a low impact energy of 25.1 J and moderate impact energy of 44.1 J were conducted for each hip protector. When the thickness of STP exceeded 8 mm, the resultant peak force tended to plateau under both impact conditions, and the force attenuation capacity decreased even under low impact energy conditions. Thus, a hip protector with a 6 mm or 8 mm STP and 5 mm foam was recommended. The STP was the key factor affecting force attenuation capacity, not the polyurethane foam. However, the foam also played an important role in helping the STP function and improving compliance for users.