Magnitude Of Yield Stress Research Articles

Plastocapillarity: Partial and full Newtonian drop embedding into immiscible yield stress substrates

HypothesisRecent advances have been made in elastocapillarity; reversible 3D deformations of solid substrates with low elastic moduli from the surface tension of deposited drops. This study explores permanent deformations caused by liquid drops on immiscible yield stress substrates. We hypothesize that the substrate's rheological properties play a major role in determining the shape and stability of the drop-substrate interface, and govern partial or full embedding into the substrate. ExperimentsSubstrate yield stress magnitudes are modified through altering the mixture ratios of petroleum jelly to paraffin oil. Water drops are deposited on substrates and deformation profiles of the deformed interface are quantified. FindingsAbove a critical Bingham-Capillary number, which characterizes the ratio of yield stress magnitude to surface tension, deposited water drops deform the substrate surface permanently, but minimally. Below this value, drops become increasingly embedded as the substrate yield stress magnitude decreases, with larger indentation depths and increased circumferential ridge heights. With sufficiently low yield stress magnitudes, where surface tension forces dominate over yield stress forces, the plastically deformed ridges fully encapsulate the liquid drop surface, resulting in full drop embedding within the substrate. These results advance knowledge of interfacial wetting on soft yield stress substrates and has implications for binary fluids, functional materials, and new drug delivery systems.

Incorporation of Lepidium perfoliatum seed gum into wheat starch affects its physicochemical, viscoelastic, pasting and freeze-thaw syneresis properties

This study aimed to investigate the influence of incorporating Lepidium perfoliatum seed gum (LPSG) into wheat starch (WS) at various mixing ratios on its FTIR, DSC, steady and dynamic rheological properties, pasting attributes, syneresis, and particle size distributions characteristics. The interaction between WS and LPSG was purely based on hydrogen-bonding. It was found that the onset (To) and peak (Tp) temperatures of the LPSG-rich mixtures increased by 10 % and 8 %, respectively, while the enthalpy (ΔH) decreased by 70 % compared to WS. A higher LPSG ratio led to a decrease in the frequency dependence of storage modulus (G′), as well as an increase in the pseudoplasticity of the mixtures. The in-shear structural recovery test showed that the rate of recovery (R, %) increased with an increasing LPSG ratio. The pasting results demonstrated that the 9/1 ratio had the highest final viscosity and the lowest relative breakdown. Applying 1 to 5 freeze-thaw cycles resulted in a 50 % to 70 % decrease in syneresis for the 9/1 mixing ratio in comparison to WS, respectively. The incorporation of LPSG into WS resulted in higher static and dynamic magnitudes of yield stress, as well as an increase in particle size when compared to WS.

Yield stress analysis of cellulose nanocrystals (CNCs) in hyaluronic acid suspensions

Due to their biodegradability features, cellulose nanocrystals (CNCs) and hyaluronic acid (HA) have been simultaneously used in the matrix of hydrogels for biomedical applications, such as corneal transplantation, and skin regeneration. Although rheology of these hydrogels may provide useful information for their applications, little to no attention has been paid to rheological characterization. In this study, we analyzed the rheology of HA-CNC suspensions and more specifically their yielding behavior. Through different rheological experiments, known as stress ramp, shear rate ramp and amplitude sweep; it was observed that HA-CNC gels possessed two yield points. Reproducible magnitudes of yield stress were obtained by optimizing the experimental conditions. The rheo-optics characterizations confirmed that the first and second yield points could be attributed to the bond and cage breakage phenomena. Studying the effect of concentration, the second yield stress increased linearly by CNC concentration, whereas the first yield point manifested a power-law dependence on concentration (exponent of 0.5). This power-law relationship was further justified by the evolution of average distance between the CNC individual particles (d), calculated through SAXS analysis.

Physicochemical and Rheological Properties of Cross‐Linked Litchi Kernel Starch and Its Application in Development of Bio‐Films

AbstractIn this study, starch from a non‐conventional source, that is, litchi is extracted and cross‐linked (CL) with varying concentrations (1%, 3%, and 5%) of sodium trimetaphosphate (STMP). The starches are characterized for their physicochemical, pasting, rheological, and thermal properties. Bio‐films are also prepared from these starches and analyzed for selected barrier and mechanical properties. The results indicate that an increase in cross linking agent concentration resulted in a significant decrease in amylose content, swelling power (SP), and solubility of starches. Peak viscosity (PV) and breakdown viscosity (BV) of CL starches are lower in comparison to native starch. Steady shear properties reveal that magnitudes of yield stress (σo) and consistency index (K) decrease upon increase in the concentration of cross linking reagent. CL starches exhibit significantly (p < 0.05) higher transition temperatures than native starch. Native starch film shows water solubility of 43.66% while for films from CL starches, the values ranged between 35.12 and 41.53%. Significant (p < 0.05) reduction in water vapor permeability (WVP) values of CL starch films (1.24–1.52 g m Pa−1 s−1 m−2) is observed in comparison to native (2.32 g m Pa−1 s−1 m−2) starch films. Cross linking significantly improves tensile strength (TS) of films, however, films elongation is lower (14.71–17.97%) than native starch film (19.88%).

Yield stress and rheology of a self-associating chitosan solution

We report that aqueous solutions of high molecular weight chitosan display a regime of shear thinning at low shear rates that is consistent with the existence of an apparent yield stress. The concentration-dependent scaling of the apparent yield stress, σ0(c)~c2.8±0.2 in the concentration range c = 7.50–65.0 mg/mL, is consistent with a solution microstructure of fractal clusters. Dynamic light scattering measurements at high concentration indicate extremely slow microdynamics, consistent with the presence of a structured network or glassy fluid. At shear rates above yielding, a constant viscosity plateau was observed with concentration-dependent scaling below the gel point consistent with existing models of entangled and associating polymers. The addition of urea, a hydrogen bond and hydrophobic interaction disrupter, did not change the reported concentration-dependent scaling of the apparent yield stress or the plateau viscosity but did weaken the apparent yield stress magnitude by ~ 30% on average.

Numerical simulations of rock blasting damage based on laboratory-scale experiments

In order to study the damage induced by rock blasting, a numerical simulation method based on the Johnson–Holmquist II (JH-2) damage model combined with the arbitrary Lagrangian–Eulerian (ALE) method is proposed. The process of dynamic breakage and damage evolution of Barre granite is reproduced using explicit hydrocode, ANSYS/LS-DYNA, based on the prototype experiments in the laboratory. The results show that both the crack patterns and measured pressures are in agreement with the results from the lab-scale experiments. The attenuation curves of the pressure and particle peak velocity (PPV) along the radial direction are respectively determined, and the corresponding theoretical formulas are summarized together with the most suitable attenuation exponent α. In addition, comparisons of blasting tests separately carried out using the discrete element method-smoothed particle hydrodynamics hybrid method and the ALE/JH-2 method demonstrate similar crack patterns formed both in intact rock disks and jointed rock disks. In the jointed rock disk, the pressure sharply declines when crossing the joint surface, while the PPV close to the joint increases before going across the joint surface, representing the 'weak transmission—strong reflection' effect of the joint surface. Different yield stresses of joint properties are further studied, which indicate that joints with a lower magnitude of yield stress can prevent more transmissions of waves crossing the joint surface. In future studies, the ALE method combined with the JH-2 damage model can be applied to larger-scale rock engineering problems to optimize the blasting design.

Magnetoviscoelastic characteristics of superparamagnetic oxides (Fe, Ni) based ferrofluids

Ferrofluids have been popular among the academic and scientific communities owing to their intelligent physical characteristics under external stimuli and are in fact among the first nanotechnology products to be employed in real world applications. However, studies on the magnetoviscoelastic behavior of concentrated ferrofluids, especially of superparamagnetic oxides of iron and nickel are rare. The present article comprises the formulation of magneto-colloids utilizing the three various metal oxides nanoparticles viz. Iron (II, III) oxide (Fe3O4), Iron (III) oxide (Fe2O3) and Nickel oxide (NiO) in oil. Iron (II, III) oxide based colloids demonstrate high magnetoviscous characteristics over the other oxides based colloids under external magnetic fields. The maximum magnitude of yield stress and viscosity is found to be 3.0kPa and 2.9kPa.s, respectively for iron (II, III) oxide based colloids at 2.6vol% particle concentration and 1.2T magnetic field. Experimental investigations reveal that the formulated magneto-nanocolloids are stable, even in high magnetic fields and almost reversible when exposed to rising and drop of magnetic fields of the same magnitude. Observations also reveal that the elastic behavior dominates over the viscous behavior with enhanced relaxation and creep characteristics under the magnetic field. The effect of temperature on viscosity and yield stress of magneto-nanocolloids under magnetic fields has also been discussed. Thus, the present findings have potential applications in various fields such as electromagnetic clutch and brakes of automotive, damping, sealing, optics, nanofinishing etc.

MR 流体を用いた遭遇型ビジュアルハプティックディスプレイの開発

This paper proposes a visual haptic display with an encountered-type haptic interface using MR (Magneto-Rheological) fluid. The proposed system can display arbitrary force by controlling the magnitude of yield stress of MR fluid and provide realistic visualization by displaying computer graphics images on the container of MR fluid directly. An operator can feel resistance force by putting instruments in the MR fluid container and can sense reality by virtue of the visual display on the MR fluid container. This type of system would be useful for surgical simulator since an operator can freely move and easily change the instruments as in real operation. In this paper, one of the fundamental surgery operations, cutting elastic strings like a blood vessel, is applied to this simulator with an open-loop cutting force control.

Characterization of material property variation across an inertia friction welded CrMoV steel component using the inverse analysis of nanoindentation data

In this study, a new application of the inverse analysis of the depth-sensing indentation technique based on the optimization theory has been satisfactorily demonstrated. The novel approach for determining the mechanical properties from experimental nanoindentation curves has been applied in order to generate the elastic–plastic stress–strain curves of three phases located across the joint of a like-to-like inertia friction weld of a CrMoV steel, i.e. the parent phase of tempered martensite and two child phases formed during the IFW process, martensite in the quenched and over-tempered condition. The inverse analysis carried out in this study consists of an optimization algorithm implemented in MATLAB, which compares an experimental nanoindentation curve with a predicted indentation curve generated by a 3D finite element model developed using the ABAQUS software; the optimization algorithm modifies the predicted curve by changing the material properties until the best fit to the experimental nanoindentation curve is found. The optimized parameters (mechanical properties) have been used to generate the stress–strain relationships in the elastic–plastic regime that can be used to simulate numerically the effects of the variation in material properties arising from phase transformations occurring across the joint during the IFW process of a CrMoV steel.The proposed inverse analysis was capable of fitting experimental load–depth (P–h) curves produced with a Nanoindentation Nanotest NTX unit from three characteristic regions located across the joint where the above mentioned phases are known to exist. The capability of the inverse analysis to build the stress–strain relationship in the elastic–plastic regime using the optimized mechanical properties of the parent metal has been validated using experimental data extracted from the compressive test of an axisymmetric sample of tempered martensite [1]. According to previous experimental studies, the presence of martensite in the quenched and over-tempered condition formed during the IFW of shaft sections of CrMoV steel are responsible of the 1.52:1 harder and 0.75:1 softer regions, compared to the region where the tempered martensite is located [2–4]. These ratios are in very good agreement with the optimized magnitudes of yield stress provided by the inverse analysis, that is, 1.54:1 for the quenched martensite and 0.68:1 for the over-tempered martensite, compared to the optimized value of yield stress of the tempered martensite. Moreover, a relative difference of less than 1.5% between the experimental and predicted maximum depth (hmax) supports the capability of the method for extracting the elastic–plastic mechanical properties defining each of the indented regions.

Field-dependent characteristics of magnetorheological fluids containing corroded iron particles

Magnetorheological (MR) devices in vehicle applications and robotic systems require both consistent control performance and reliable operation. However, corrosion of iron particles in MR fluid may occur during long-time operation. This corrosion behavior can significantly affect the performance and reliability of application devices or systems utilizing MR fluids. This study experimentally investigates the effect of the MR particle corrosion on the performance of MR fluids in terms of the field-dependent yield stress magnitude and shear stress controllability. MR particles are first corroded by two different liquids; water–sodium chloride solution and water–calcium chloride solution. The resulting MR particles are examined by scanning electron microscopy and their molar ratios are analyzed by energy dispersive x-ray analysis. Using the corroded MR particles, MR fluid is synthesized for evaluation of the effects on its characteristics. A rotational viscometer is used to measure the field-dependent shear stress and response time. The measured results are compared between the original MR fluid composed of the non-corroded iron particles and the MR fluid composed of the corroded iron particles. In addition, the effect of the corroded particles in MR fluid on the shear stress controllability is investigated in the time domain.

Rheological investigation of body cream and body lotion in actual application conditions

The objective of the present study is to systematically evaluate and compare the rheological behaviors of body cream and body lotion in actual usage situations. Using a strain-controlled rheometer, the steady shear flow properties of commercially available body cream and body lotion were measured over a wide range of shear rates, and the linear viscoelastic properties of these two materials in small amplitude oscillatory shear flow fields were measured over a broad range of angular frequencies. The temperature dependency of the linear viscoelastic behaviors was additionally investigated over a temperature range most relevant to usual human life. The main findings obtained from this study are summarized as follows: (1) Body cream and body lotion exhibit a finite magnitude of yield stress. This feature is directly related to the primary (initial) skin feel that consumers usually experience during actual usage. (2) Body cream and body lotion exhibit a pronounced shear-thinning behavior. This feature is closely connected with the spreadability when cosmetics are applied onto the human skin. (3) The linear viscoelastic behaviors of body cream and body lotion are dominated by an elastic nature. These solid-like properties become a criterion to assess the selfstorage stability of cosmetic products. (4) A modified form of the Cox-Merz rule provides a good ability to predict the relationship between steady shear flow and dynamic viscoelastic properties for body cream and body lotion. (5) The storage modulus and loss modulus of body cream show a qualitatively similar tendency to gradually decrease with an increase in temperature. In the case of body lotion, with an increase in temperature, the storage modulus is progressively decreased while the loss modulus is slightly increased and then decreased. This information gives us a criterion to judge how the characteristics of cosmetic products are changed by the usual human environments.

Cementitious grouts with adapted rheological properties for injection by vacuum techniques

The injection of cementitious-based grouts by vacuum pressure techniques is expected to extract part of the mixing water with direct consequences on the fresh and hardened properties. A research program was undertaken to evaluate the effect of vacuuming on the amount of water extracted along with resulting changes in grout properties including flowability, static yield stress, viscosity, unit weight, Wick-induced bleeding, and compressive strength. Tests were conducted using specimens sampled right after mixing as well as after being subjected to vacuum. Test results have shown that the extraction of water decreases fluidity (i.e., flow time and mini-slump cone) and increases the magnitude of yield stress and viscosity, mostly due to increased internal friction and cohesion within the solid particles. Grouts prepared with low water-to-cementitious materials ratio and containing moderate to high concentrations of viscosity-modifying admixtures yielded adequate water retentivity, with minor variations in rheological and hardened properties.

Gelation of aqueous clay mineral dispersions leaching at low pH: Effect of mineral/pulp composition and temperature

Presence of gangue aluminosilicate clay (e.g., muscovite) minerals plays an important role in controlling mineral ore processability and extraction of valuable metals (e.g., copper, gold). Hydrometallurgical processing of clay containing minerals at low pH (~1) and elevated temperature (e.g., 70°C) sometimes leads to deleterious viscous gel formation nominally ascribed to leached Si(IV) polycondensation. In this study, the leaching and gelation behaviour of 30–57wt.% solid muscovite dispersions was investigated at pH 1 with a particular focus on the role of mineral chemistry (low-Fe vs. high-Fe substituted muscovite), temperature (25 and 70°C) and supernatant Si(IV) and Al(III) concentration (0.1–1.5M). The temporal particle interactions, reflecting the extent of gelation was characterized by pulp shear rheology. At 25°C, low yield stress was initially displayed by low-Fe muscovite dispersion whilst the high-Fe muscovite dispersion formed a gel. At 70°C, however, both dispersions initially displayed lower yield stress. In all cases, the magnitude of yield stress systematically attenuated in the course of 4h aging. The lower shear yield stresses observed at 70°C correlated with significantly lower concentration (<0.1M) of leached Si(IV). Whilst the increase of the solution Si(IV) concentration of 0.25–1M had no impact on rheology of dispersions at 25°C, strong gelation occurred within 2h in the presence of 1M Si(IV) at 70°C. The gelation induction time decreased with increasing solution Al(III) concentration or dispersion solid content, whilst it was completely absent at lower Si(IV) concentrations. Results demonstrated that the proliferation and polycondensation of Si(IV) species alone is necessary but not sufficient cause of gelation which occur at lower Si(IV) concentrations (e.g., 0.25M) under plant conditions, albeit other species (e.g., Al(III) and Fe(III)) prevail. Both intense heating and higher Si(IV) concentration are shown to be conducive to gelation.

In-plane anisotropy in tensile deformation and its influence on the drawability of Nimonic c–263 alloy sheets

An effort has been made to comprehensively evaluate and rationalize the in-plane anisotropy in tensile properties and the effect of aging on the nature of deformation (strain hardening behaviour) and formability characteristics, especially the limit drawing ratio and forming limit diagram. Despite weak crystallographic texture and excellent ductility and high work hardening exponents, the alloy sheets of C-263 exhibit significant extent of in-plane anisotropy in its tensile properties and yield loci. The absolute magnitudes of yield stress and the exact nature of anisotropy that can be predicted from the tensile part of the yield locus need to be employed with caution. This is because when the magnitudes of the yield stresses, obtained from yield locus are more than 5 times higher as compared to the yield and ultimate tensile strength values and the nature and degree of in-plane anisotropy under tensile loading matches with that of only the compressive yield stresses of yield locus. The alloy sheet, due to weak crystallographic texture and relatively high strengths, is found to be far more suitable for structural applications, rather than for deep drawing applications, which was reflected in low limit drawing ratio values (1.34 for CR+ST and 1.23 for peak aged conditions). Further, the study conducted reveals that the safer forming limits in strain space is higher for CR+ST condition; while, the safer forming limits in stress space are higher for peak aged (CR+ST+1073 K/8 h) condition. Finally, detailed studies are outlined to arrive at suitable microstructural and textural characteristics that provide significantly enhanced drawability in the Nimonic C-263 alloy sheets.

Steady and dynamic oscillatory shear rheological properties of ketchup–processed cheese mixtures: Effect of temperature and concentration

The steady and dynamic shear properties of ketchup–processed cheese (K–PC) mixtures were investigated at different temperatures (10–50 °C) and PC concentrations (0–30%). The K–PC mixtures showed a shear-thinning behavior with low magnitudes of yield stress. The consistency coefficient ( K) and apparent viscosity ( η 50) decreased with increase in temperature and concentration. The mixtures followed the Arrhenius temperature relationship, indicating that the magnitudes of activation energies ( E a ) were in the range of 8.83–17.16 kJ mol −1. Storage ( G′), loss ( G′′) and complex ( G∗) modulus increased with increase in frequency while complex viscosity ( η∗) decreased. The K–PC mixtures at concentrations of 0–15% exhibited weak gel-like behavior. Increase in the PC concentration resulted in a decrease in G∗, G′, G′′ and η∗ up to the 15% of PC concentration, showing a plateau value between 0% and 30% concentrations. Cox–Merz rule was not applicable to K–PC mixtures.

Motion and shape of an axisymmetric viscoplastic drop slowly falling through a viscous fluid

Slow sedimentation of a deformable drop of Bingham fluid in an unbounded Newtonian medium is studied using a variation of the integral equation method (Toose et al., J Eng Math 30:131–150, 1996, Int J Numer Methods Fluids 30:653–674, 1999). The Green function for the Stokes equation is used, and the non-Newtonian stress is treated as a source term. The computations are performed for a range of physical parameters of the system. It is demonstrated that initially deformed drop similar to Newtonian ones breaks up for high capillary number, Ca, and stabilizes to steady shapes at low Ca. Estimations of critical capillary number for specific initial deformations demonstrated its growth (increase in the stability of the drop) with the yield stress magnitude both for prolate and oblate initial shapes. Prolate initial shapes become more stable with the increase of the plastic viscosity. In contrast to this, for low yield stress, oblate shapes are destabilized with the growth of the plastic viscosity. This effect is similar to the effect of the viscosity of a Newtonian drop on its stability. However, at higher yield stress, the effect of plastic viscosity is reversed.

Modeling crack closure and damage in variable amplitude fatigue using smooth specimen fatigue test data

During overloads in variable amplitude fatigue, local stresses at small cracks growing from notches reach yield stress magnitude. Such high stress levels result in a large decrease in crack opening stress and an increase in the fatigue damage of subsequent smaller stress cycles. This paper presents a methodology for modeling changes in crack opening stress level and fatigue damage using data derived from periodic underload fatigue tests of smooth specimens. Predicted crack closure stress levels agree well with those obtained from crack growth observations made with a high magnification microscope.

Determination of Dominant Factors in High Accuracy Prediction of Welding Distortion

The experiment was carried out using a bead-on-plate specimen with the groove placed to accurately predict welding distortion. The experiment was simulated with thermal elastic-plastic analysis based on FEM. Comparing and investigating both results, the dominant factors for high accuracy prediction of welding distortion were determined. In the thermal elastic-plastic analysis, the yield condition should be satisfied regardless of the magnitude of yield stress of the material. It was not known if the predicted results of welding distortion obtained without satisfying the yield condition in the whole temperature range were overestimated or underestimated. The accuracy of prediction of welding distortion was improved by applying heat input to the weld metal bead shape, not just the groove profile. It was determined that satisfying the yield condition in the entire temperature range and considering the weld metal shape as the deposited metal were the dominant factors for high accuracy prediction of welding distortion.

The spreading behaviour of capillary driven yield-stress drops

Surface tension driven spreading of viscoplastic drops after impact on a solid substrate is investigated experimentally and compared with purely shear-thinning drops. It is shown that the spreading rate is affected independently both by the degree of fluid shear-thinning and by the yield-stress magnitude. Moreover, spreading can be inhibited when the yield-stress becomes greater than a critical value, preventing drops from assuming a spherical cap shape with a static contact angle consistent with the Young–Laplace equation. This critical value can be related to a transition between capillary governed and viscoplastic governed behaviour, with the regime change characterised by the ratio of capillary pressure to yield-stress magnitude.

The free-fall of viscoplastic drops

The free-fall of liquid drops under the action of gravity is studied experimentally by high-speed imaging, with focus on drops of viscoplastic fluids (i.e., those materials which exhibit a fluid behaviour only when the applied stress exceeds a certain threshold value, called the yield stress), and compared to the behaviour observed in Newtonian drops. The yield stress of the fluid is shown to alter significantly the drop shape during free-fall. The results can be interpreted in terms of a dimensionless number comparing the yield stress magnitude and the capillary pressure.