Modeling of the Non-Linear Rheological Behavior of a Lubricating Grease at Low-Shear Rates

1999 ◽  
Vol 122 (3) ◽  
pp. 590-596 ◽  
Author(s):  
Jose´ M. Madiedo ◽  
Jose´ M. Franco ◽  
Concepcio´n Valencia ◽  
Crı´spulo Gallegos
Keyword(s):  
Steady State ◽  
Stress Relaxation ◽  
Normal Stress ◽  
Rheological Behavior ◽  
Linear Viscoelasticity ◽  
Relaxation Spectrum ◽  
Lubricating Grease ◽  
Shear Rates ◽  
Non Linear ◽  
Low Shear

This paper deals with modeling the non-linear rheological behavior of lubricating greases at very low shear rates. With this aim, dynamic linear viscoelastic, non-linear stress relaxation, transient and steady-state shear flow, and transient first normal stress difference measurements have been carried out on a diurea-derivative lubricating grease. A factorable non-linear viscoelasticity model, the Wagner integral model, derived from the K-BKZ constitutive equation, was used in order to predict the non-linear rheological response of the above-mentioned lubricating grease under shear. The time-dependent part of the model was described by its linear relaxation spectrum, whilst two different damping functions (Wagner and Soskey-Winter’s damping functions) were analysed as the strain-dependent factor. The continuous linear relaxation spectrum was estimated, using regularization techniques, from the dynamic linear viscoelasticity functions. The damping function was calculated from non-linear stress relaxation tests. The constitutive model, with Soskey-Winter’s damping function, predicted the steady-state flow curve, the transient shear stress and the transient first normal stress differences of the lubricating grease studied fairly well. [S0742-4787(00)01603-9]

Microstructure and rheological behavior of hypereutectic semi-solid Al–Si alloy under low shear rates compression test

2008 ◽  
Vol 492 (1-2) ◽  
pp. 377-382 ◽  
Author(s):  
Omid Lashkari ◽  
Frank Ajersch ◽  
Andre Charette ◽  
X.-Grant Chen
Keyword(s):  
Compression Test ◽  
Rheological Behavior ◽  
Shear Rates ◽  
Semi Solid ◽  
Low Shear

Rheology and Component Interactions in Tape Casting Slurries

1985 ◽  
Vol 60 ◽  
Author(s):  
John R Morris ◽  
W Roger Cannon
Keyword(s):  
Shear Rate ◽  
Rheological Behavior ◽  
Tape Casting ◽  
Relative Viscosity ◽  
Shear Rates ◽  
Viscosity Measurements ◽  
The Stability ◽  
Low Shear

AbstractRheology and the component interactions which affect rheology were studied for a tape casting composition similar to commercial systems. Viscosity measurements at different shear rates were compared to measured tape properties to determine if high or low shear rate rheological behavior controls tape characteristics. Relative viscosity was measured to assess the contribution of each component to the stability of the dispersion.

Calculation of Complex Viscosities from Slow-Speed Transient Torque Measurements with the Mooney Rheometer

1982 ◽  
Vol 55 (5) ◽  
pp. 1426-1436 ◽  
Author(s):  
N. Nakajima ◽  
E. R. Harrell
Keyword(s):  
Steady State ◽  
Shear Rate ◽  
Practical Interest ◽  
Actual Process ◽  
Steady State Flow ◽  
Shear Rates ◽  
State Flow ◽  
Lower Shear ◽  
Rate Limit ◽  
Low Shear

Abstract It has been customary to assign certain time scales to given polymer processes. For example, the extrusion process is said to occur at a shear rate in the order of some hundred reciprocal seconds and injection molding at some thousand reciprocal seconds or higher. These statements are usually accompanied by instructions that the viscosity of a material is to be measured at the respective shear rate in order to characterize its processability. However, the above argument is only partially valid, and a single-point viscosity measurement is only a part of the processability evaluation. Inadequacy of the above rationale has been recognized by industry for a long time. With the rapid growth of plastics production in the 1960's, plastic processing went through a technological evolution. In the early stage of evolution of various fabrication techniques, development of suitable grades of material for the respective processes was the major effort of the plastic producers. Soon it became clear that resins which had the same viscosity at the so-called processing shear rate often behaved differently in the actual process. This led to the measurement of the steady-state flow properties at lower shear rates than the so-called processing shear rate, which was representative of the highest shear rate involved in the process. The significant observation was that the viscosity differences of resins often were magnified at the lower shear rate. Sometimes, a subtle difference in processability corresponded to a viscosity difference observable only at very low shear rates. Thus, acquisition of the steady-state flow curve from the low-shear-rate limit (i.e., the Newtonian viscosity) to the high shear rate limit (i.e., the limiting power-law region) became a subject of practical interest. The characterization of such flow curves and their relation to molecular weight distribution (MWD) became a subject of intense study for commercial plastics having a large variation in MWD.

scholarly journals A theoretical investigation of the frisbee motion of red blood cells in shear flow

2021 ◽  
Vol 16 ◽  
pp. 23
Author(s):  
Thierry Mignon ◽  
Simon Mendez
Keyword(s):  
Steady State ◽  
Shear Flow ◽  
Blood Cell ◽  
Red Blood Cells ◽  
Red Blood Cell ◽  
Blood Cells ◽  
Numerical Solutions ◽  
Shear Rates ◽  
Steady State Solutions ◽  
Low Shear

The dynamics of a single red blood cell in shear flow is a fluid–structure interaction problem that yields a tremendous richness of behaviors, as a function of the parameters of the problem. A low shear rates, the deformations of the red blood cell remain small and low-order models have been developed, predicting the orientation of the cell and the membrane circulation along time. They reproduce the dynamics observed in experiments and in simulations, but they do not simplify the problem enough to enable simple interpretations of the phenomena. In a process of exploring the red blood cell dynamics at low shear rates, an existing model constituted of 5 nonlinear ordinary differential equations is rewritten using quaternions to parametrize the rotations of the red blood cell. Techniques from algebraic geometry are then used to determine the steady-state solutions of the problems. These solutions are relevant to a particular regime where the red blood cell reaches a constant inclination angle, with its membrane rotating around it, and referred to as frisbee motion. Comparing the numerical solutions of the model to the steady-state solutions allows a better understanding of the transition between the most emblematic motions of red blood cells, flipping and tank-treading.

Study on Shear Rheological Behavior of Konjac Glucomannan

2011 ◽  
Vol 52-54 ◽  
pp. 1332-1335 ◽  
Author(s):  
Chao Wang ◽  
Mei Xu ◽  
Yu Peng Zhu ◽  
Yu Qiao ◽  
Ting Ting Liang
Keyword(s):  
Rheological Behavior ◽  
Food Industry ◽  
Polynomial Equation ◽  
Konjac Glucomannan ◽  
Flow Index ◽  
Pseudoplastic Fluid ◽  
Linear Change ◽  
Shear Rates ◽  
Non Linear ◽  
Viscosity Factor

Konjac glucomannan (KGM) belongs to pseudoplastic fluid. Remarkable non-linear change tendencies of shear rheological behavior of KGM were detected through analysis of the correlation of viscosity (η)-shear rates and shear stress-shear rates respectively, and its shear rheological curves conformed to the Power Law (τ=ＫDn). The change tendencies of viscosity factor (K) and flow index (n) correlated with concentration and temperature were also obtained, the curves can be fitted by power and quadratic polynomial equation respectively. The acquired non-linear correlation curves of K and n can provide reliable foundation for rational applications of KGM in food industry and its grade estimation.

Non-linear rheological behavior of superplasticized cementitious suspensions at high shear rates

2021 ◽  
Vol 306 ◽  
pp. 124825
Author(s):  
Ángel De La Rosa ◽  
Lucía Garijo ◽  
Gonzalo Ruiz ◽  
Rodrigo Moreno
Keyword(s):  
Rheological Behavior ◽  
High Shear ◽  
Shear Rates ◽  
High Shear Rates ◽  
Non Linear

Pre-Treatment Steady-State Rheology Predicts Response to Hydroxyurea in Patients with Sickle Cell Disease

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 3661-3661
Author(s):  
Alessandro Baldan ◽  
Carly Ginter Summerall ◽  
Loretta James ◽  
Bogdan R. Dinu ◽  
Jonathan M. Flanagan ◽  
...  
Keyword(s):  
Steady State ◽  
Blood Rheology ◽  
High Shear ◽  
Cell Disease ◽  
Shear Rates ◽  
High Shear Rates ◽  
Baseline Values ◽  
The Mean ◽  
Pre Treatment ◽  
Low Shear

Abstract Background: Patients with sickle cell disease (SCD) have altered blood rheology due to erythrocyte abnormalities, such as increased aggregation and RBC density. The hematocrit to viscosity ratio (HVR) is a measure of RBC oxygen carrying capacity, and is reduced in SCD. Higher percent dense red blood cells (%DRBC) and lower HVR have been associated with higher rates of disease related complications. The aim of this study was to elucidate the effects of hydroxyurea (HU), fetal hemoglobin (HbF) and transfusion therapy (TF) on the rheology of patients with SCD. Methods: We measured whole blood viscosity of samples from children with SCD at low shear (45 s-1) and high shear (225 s-1) using a Brookfield cone and plate viscometer under oxygenated conditions. Venous blood samples in EDTA were analyzed within 4 hours of phlebotomy. Laboratory values were obtained with a Siemens ADVIA120 Hematology System; Hb profiles by high performance liquid chromatography. Samples were collected at routine clinic visits from SCD patients prior to initiation of therapy (n=105 for HbSS, n=77 for HbSC), then on HU at MTD, (n=30 for HbSS, n=13 for HbSC), or at least one week after TF (n=32). A paired T-test was used to assess treatment changes; correlation/trend tests were used to test association of hematological and rheology parameters. Results: Blood viscosities at low and high shear rates were significantly higher in untreated patients with HbSC compared to untreated patients with HbSS (p<0.001), while HVR was similar between patients with HbSC or HbSS. High endogenous HbF levels were significantly associated with higher HVR 225 s-1 in patients with HbSS but not HbSC. Patients with HbSS after TF had a significant improvement (rise) in their HVR at high shear (p=0.04) but not at low shear. This TF mediated rise in HVR 225 s-1 correlated with increased Hb (r=0.56, p<0.002), and decreased WBC and ANC (r= - 0.46 and r=- 0.36 respectively, p<0.05). Patients with greatest decreases in %HbS had most improvement in their HVR 225 s-1 (r = -0.36, p=0.15). HbSS patients treated with HU also had a rise in their HVR 225 s-1 (p=0.01) but not HVR 45 s-1. This improved HVR 225 s-1 was associated with typical HU induced changes in Hb, Hct, HbF and decreases in WBC and ANC. For HbSS patients treated with either HU or TF, a baseline HVR (at either shear rate) below the group mean experienced a greater rise in HVR, while a baseline HVR above the mean experienced a decline (p<0.001; Figure 1). HbSS patients with a pre-treatment %DRBC above the mean experienced a decline in %DRBC on HU at MTD, while those with a %DRBC below the mean did not (p=0.001).A similar trend was seen in HbSC patients treated with HU to MTD, but did not reach statistical significance. Patients with HbSC had significantly higher %DRBC compared to patients with HbSS (p<0.001). HbSC patients placed on HU had significantly higher baseline %DRBC than HbSC patients not treated with HU (15.8 ±13 versus 8.2± 6.5, p=0.001). However, HbSC patients treated to HU MTD did not experience a significant reduction in %DRBC. Individuals with HbSS and high endogenous HbF had significantly lower %DRBC (r= -0.36, p=0.002), and greater production of HbF on HU also resulted in lower %DRBC (p=0.036) in HbSS (n=25), but not HbSC patients (n=13). Conclusions: In HbSS patients, high endogenous HbF levels were significantly associated with higher HVR at high shear and with lower %DRBC, but not in HbSC patients. In HbSS patients, HU and TF therapy improved HVR at high shear rates but not low shear, possibly indicating persistent red cell adhesion at low shear rates. This improvement correlated with HbF levels in HU treated patients, and HbS levels in TF treated patients. Patients with SCD and greater than average impairment of whole blood rheology at pre-treatment steady-state experienced greater rheological improvement, demonstrated clinically by a reduction in %DRBC or a rise in HVR on HU. A cohort of 13 HbSC patients treated prospectively with HU did not demonstrate statistically significant rheological improvement, either a result of small sample size or the minimal rise in HbF despite HU therapy. Figure 1. Effect of baseline rheology on rheological changes at MTD of HU. Horizontal dotted line denotes mean baseline values. A. Patients with HbSS and a baseline HVR 45 s-1 below the mean showed an increase in HVR 45 s-1 at MTD (green dots). B. Patients with HbSS and a baseline HVR 225 s-1 below the mean showed an increase in HVR 225 s-1 at MTD (green dots). Figure 1. Effect of baseline rheology on rheological changes at MTD of HU. Horizontal dotted line denotes mean baseline values. A. Patients with HbSS and a baseline HVR 45 s-1 below the mean showed an increase in HVR 45 s-1 at MTD (green dots). B. Patients with HbSS and a baseline HVR 225 s-1 below the mean showed an increase in HVR 225 s-1 at MTD (green dots). Disclosures No relevant conflicts of interest to declare.

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