Actual Eyring Models for Thixotropy and Shear-Thinning: Experimental Validation and Application to EHD

2004 ◽  
Vol 126 (4) ◽  
pp. 728-732 ◽  
Author(s):  
Scott Bair
Keyword(s):  
High Pressure ◽  
Film Thickness ◽  
Experimental Validation ◽  
Shear Thinning ◽  
Anomalous Behavior ◽  
Sliding Contact ◽  
Modern Methods ◽  
Eyring Model ◽  
Using Data ◽  
Limited Usefulness

The Eyring sinh law is presently the most well-accepted model for shear-thinning of EHD lubricants at high pressure. It was, however, not accepted for this purpose by Eyring, who found it to be of only limited usefulness for thixotropy. Then, it is extremely important that these models receive a critical review using data obtained by modern methods to evaluate the actual Eyring models and show how they differ from the model in use today. Data from high-pressure viscometers were used to validate the actual Eyring models. The Ree-Eyring model for shear-thinning obeys time-temperature-pressure superposition. A film thickness calculation shows it to suffer from the same anomalous behavior in sliding contact as does the sinh law.

The Actual Eyring Models for Thixotropy and Shear-Thinning: Experimental Validation and Application to EHD

2004 ◽  
Author(s):  
Scott Bair
Keyword(s):  
High Pressure ◽  
Film Thickness ◽  
Experimental Validation ◽  
Shear Thinning ◽  
Anomalous Behavior ◽  
Sliding Contact ◽  
Modern Methods ◽  
Eyring Model ◽  
Using Data ◽  
Limited Usefulness

The Eyring sinh law is presently the most well accepted model for shear-thinning of EHD lubricants at high pressure. It was, however, not accepted for this purpose by Eyring who found it to be of only limited usefulness for thixotropy. Then, it is extremely important that these models receive a critical review using data obtained by modern methods to evaluate the actual Eyring models and show how they differ from the model in use today. Data from high-pressure viscometers were used to validate the actual Eyring models. The Ree-Eyring model for shear-thinning obeys time-temperature-pressure superposition. A film thickness calculation shows it to suffer from the same anomalous behavior in sliding contact as does the sinh law.

New Central Film Thickness Equation for Shear Thinning Lubricants in Elastohydrodynamic Lubricated Rolling/Sliding Point Contact Conditions

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Puneet Katyal ◽  
Punit Kumar
Keyword(s):  
High Pressure ◽  
Equation Of State ◽  
Film Thickness ◽  
Point Contact ◽  
Viscosity Coefficient ◽  
Shear Thinning ◽  
Numerical Approach ◽  
Present Formulation ◽  
Contact Conditions ◽  
Doolittle Equation

This paper offers central film thickness formula pertaining to shear-thinning lubricants under rolling/sliding point contact conditions. The shear-thinning behavior of the lubricants is modeled using Carreau viscosity equation and the piezo-viscous response employed herein is the free-volume based Doolittle equation in conjunction with Tait's equation of state for lubricant compressibility. The present formulation is based on reciprocal asymptotic isoviscous piezo-viscous coefficient as it is a more accurate measure of the high pressure piezo-viscous response of elastohydrodynamic lubricated (EHL) lubricants compared to the conventional pressure–viscosity coefficient. Comparisons between simulated, curve-fitted values, and experimental results validate both the employed numerical approach and rheological model.

scholarly journals Challenges in Bridge Health Monitoring: A Review

Sensors ◽  
2021 ◽  
Vol 21 (13) ◽  
pp. 4336
Author(s):  
Piervincenzo Rizzo ◽  
Alireza Enshaeian
Keyword(s):  
United States ◽  
Health Monitoring ◽  
Highway Bridges ◽  
The United States ◽  
Anomalous Behavior ◽  
Existing Structures ◽  
Bridge Health Monitoring ◽  
Using Data ◽  
The Many ◽  
Major Factors

Bridge health monitoring is increasingly relevant for the maintenance of existing structures or new structures with innovative concepts that require validation of design predictions. In the United States there are more than 600,000 highway bridges. Nearly half of them (46.4%) are rated as fair while about 1 out of 13 (7.6%) is rated in poor condition. As such, the United States is one of those countries in which bridge health monitoring systems are installed in order to complement conventional periodic nondestructive inspections. This paper reviews the challenges associated with bridge health monitoring related to the detection of specific bridge characteristics that may be indicators of anomalous behavior. The methods used to detect loss of stiffness, time-dependent and temperature-dependent deformations, fatigue, corrosion, and scour are discussed. Owing to the extent of the existing scientific literature, this review focuses on systems installed in U.S. bridges over the last 20 years. These are all major factors that contribute to long-term degradation of bridges. Issues related to wireless sensor drifts are discussed as well. The scope of the paper is to help newcomers, practitioners, and researchers at navigating the many methodologies that have been proposed and developed in order to identify damage using data collected from sensors installed in real structures.

The High Pressure Rheology of Mixtures

2004 ◽  
Vol 126 (4) ◽  
pp. 697-702 ◽  
Author(s):  
Scott Bair
Keyword(s):  
Molecular Weight ◽  
High Pressure ◽  
Binary Systems ◽  
Viscosity Coefficient ◽  
Shear Thinning ◽  
Newtonian Viscosity ◽  
Double Shear ◽  
Ideal Mixing ◽  
Viscosity Behavior ◽  
Single Flow

The Newtonian mixing rules for several binary systems have been experimentally investigated. Some systems show non-ideal mixing response and for some systems the non-ideal response is pressure-dependent, yielding an opportunity for manipulation of the pressure-viscosity behavior to advantage. The mixing of differing molecular weight “straight cuts” can produce very different pressure-viscosity response. This behavior underscores the difficulty in predicting the pressure-viscosity coefficient based upon chemical structure and ambient viscosity since the molecular weight distribution is also important, but it also provides another opportunity to control the high-pressure response by blending. The first experimental observation of double shear-thinning within a single flow curve is reported. Blending then provides the capability of adjusting not only the Newtonian viscosity but also the non-Newtonian shear-thinning response as well.

scholarly journals Effect of an Improved Yasutomi Pressure-Viscosity Relationship on the Elastohydrodynamic Line Contact Problem

2013 ◽  
Vol 2013 ◽  
pp. 1-7
Author(s):  
Vincenzo Petrone ◽  
Adolfo Senatore ◽  
Vincenzo D'Agostino
Keyword(s):  
High Pressure ◽  
Film Thickness ◽  
Free Volume ◽  
Experimental Studies ◽  
Line Contact ◽  
Volume Model ◽  
Free Volume Model ◽  
Pressure Area ◽  
New Formulation ◽  
Lubricant Viscosity

This paper presents the application of an improved Yasutomi correlation for lubricant viscosity at high pressure in a Newtonian elastohydrodynamic line contact simulation. According to recent experimental studies using high pressure viscometers, the Yasutomi pressure-viscosity relationship derived from the free-volume model closely represents the real lubricant piezoviscous behavior for the high pressure typically encountered in elastohydrodynamic applications. However, the original Yasutomi correlation suffers from the appearance of a zero in the function describing the pressure dependence of the relative free volume thermal expansivity. In order to overcome this drawback, a new formulation of the Yasutomi relation was recently developed by Bair et al. This new function removes these concerns and provides improved precision without the need for an equation of state. Numerical simulations have been performed using the improved Yasutomi model to predict the lubricant pressure-viscosity, the pressure distribution, and the film thickness behavior in a Newtonian EHL simulation of a squalane-lubricated line contact. This work also shows that this model yields a higher viscosity at the low-pressure area, which results in a larger central film thickness compared with the previous piezoviscous relations.

scholarly journals Analysis of misaligned journal bearing lubrication performance considering the effect of lubricant couple stress and shear thinning

2021 ◽  
Vol 37 ◽  
pp. 282-290
Author(s):  
Junchao Zhu ◽  
Haiyu Qian ◽  
Huabing Wen ◽  
Liangyan Zheng ◽  
Hanhua Zhu
Keyword(s):  
Film Thickness ◽  
Couple Stress ◽  
Journal Bearing ◽  
Shear Thinning ◽  
Inlet Temperature ◽  
Stress Effect ◽  
Misalignment Angle ◽  
Oil Film ◽  
Stress Coefficient ◽  
Lubrication Performance

ABSTRACT This paper investigates journal bearings, and builds a lubrication model taking into account misalignment, the lubricant couple stress effect and shear thinning. In order to explore the sensitivity of couple stress fluid lubrication performance to oil film thickness, we introduce the critical oil film thickness coefficient. The results show that the sensitivity increases with the increase of the couple stress coefficient, and it is highest in the area of minimum oil film thickness. Compared with a parallel journal, increases in the misalignment angle strengthen the effect of couple stress. Shear thinning also plays an important role in bearing lubrication performance. For a low oil inlet temperature, the effect of shear thinning increases with the increase of the couple stress parameter. For a high oil inlet temperature, the influence is negligible. An increase in the misalignment angle will not further enhance the effect of shear thinning.

scholarly journals A Class of Methods for the Analysis of Blade Tip Timing Data from Bladed Assemblies Undergoing Simultaneous Resonances—Part II: Experimental Validation

2007 ◽  
Vol 2007 ◽  
pp. 1-10 ◽  
Author(s):  
J. Gallego-Garrido ◽  
G. Dimitriadis ◽  
I. B. Carrington ◽  
J. R. Wright
Keyword(s):  
Experimental Test ◽  
Experimental Validation ◽  
Test Rig ◽  
New Techniques ◽  
Analysis Techniques ◽  
Simultaneous Resonances ◽  
Timing Data ◽  
Blade Tip ◽  
Using Data ◽  
Double Resonances

Blade tip timing is a technique for the measurement of vibrations in rotating bladed assemblies. In Part I of this work a class of methods for the analysis of blade tip timing data from bladed assemblies undergoing two simultaneous synchronous resonances was developed. The approaches were demonstrated using data from a mathematical simulation of tip timing data. In Part II the methods are validated on an experimental test rig. First, the construction and characteristics of the rig will be discussed. Then, the performance of the analysis techniques when applied to data from the rig will be compared and analysed. It is shown that accurate frequency estimates are obtained by all the methods for both single and double resonances. Furthermore, the recovered frequencies are used to calculate the amplitudes of the blade tip responses. The presence of mistuning in the bladed assembly does not affect the performance of the new techniques.

Scale Effects in Generalized Newtonian Elastohydrodynamic Films

2008 ◽  
Author(s):  
I. I. Kudish ◽  
P. Kumar ◽  
M. M. Khonsary ◽  
S. Bair
Keyword(s):  
Film Thickness ◽  
Scale Effects ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Shear Thinning ◽  
Effective Pressure ◽  
Practical Advantage ◽  
Inlet Zone ◽  
Real Machine

The prediction of elastohydrodynamic lubrication (EHL) film thickness requires knowledge of the lubricant properties. Today, in many instances, the properties have been obtained from a measurement of the central film thickness in an optical EHL point contact simulator and the assumption of a classical Newtonian film thickness formula. This technique has the practical advantage of using an effective pressure-viscosity coefficient which compensates for shear-thinning. We have shown by a perturbation analysis and by a full EHL numerical solution that the practice of extrapolating from a laboratory scale measurement of film thickness to the film thickness of an operating contact within a real machine may substantially overestimate the film thickness in the real machine if the machine scale is smaller and the lubricant is shear-thinning in the inlet zone.

scholarly journals Efficacy of high-pressure balloon for the treatment of arteriovenous fistula stenosis: a meta-analysis

2021 ◽  
Author(s):  
Yu Li ◽  
Wenhao Cui ◽  
Jukun Wang ◽  
Chao Zhang ◽  
Tao Luo
Keyword(s):  
High Pressure ◽  
Arteriovenous Fistula ◽  
Meta Analysis ◽  
Cochrane Library ◽  
Technical Success Rate ◽  
Stenosis Rate ◽  
Significant Difference ◽  
Arteriovenous Fistula Stenosis ◽  
Using Data ◽  
The Cochrane Library

AbstractObjectiveThe objective of the present study was to compare the effectiveness of high-pressure balloon (HPB) versus conventional balloon angioplasty (BA) in treating arteriovenous fistula (AVF) stenosis.Materials and MethodsA meta-analysis was conducted using data acquired from PubMed, EMBASE, the Cochrane Library, SinoMed, CNKI, WanFang and VIP databases from the time the databases were established to November 2020. All analyses included in the studies comprised the subgroups of HPB and BA. The patency of AVF was compared between the two groups at 3 months, 6 months and 12 months after operation.ResultsNine studies comprising 475 patients were included in the meta-analysis. The pooled results revealed that stenosis rate of AVFs treated with HPB was significantly lower than that of AVFs treated with conventional balloon at 3 months (OR= 0.37, 95% CI 0.21 to 0.67, p<0.001) and 6 months after operation (OR= 0.33, 95% CI 0.15 to 0.75, p=0.008). In addition, the technical success rate of HPB groups was high (OR= 0.14, 95% CI 0.05 to 0.35, p<0.001). However, no significant difference was observed between the experimental and control groups at 12 months after operation (OR= 0.61, 95% CI 0.29 to 1.25, p=0.18). No significant publication bias was observed in the analyses.ConclusionHPB is a potential primary option for the treatment of AVF stenosis, with a lower 3- and 6-month stenosis rate than BA. However, the long-term effect of HPB was not satisfactory; therefore, further research should be conducted to elucidate the relationship between the two groups.

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