Bearing torque characteristics of lithium soap greases with some synthetic base oils

2012 ◽  
Vol 226 (6) ◽  
pp. 575-583 ◽  
Author(s):  
Eri Oikawa ◽  
Noriyuki Inami ◽  
Michita Hokao ◽  
Atsushi Yokouchi ◽  
Joichi Sugimura
Keyword(s):  
Yield Stress ◽  
Ball Bearing ◽  
Test Apparatus ◽  
Lower Yield ◽  
Lower Yield Stress ◽  
Force Microscopy ◽  
Base Oils ◽  
Atomic Force ◽  
Deep Groove ◽  
Lithium Soap

This article describes the influence of rheological properties on the bearing torque characteristics of the lithium soap greases with five types of base oils. The greases used had different yield stress depending on the base oils even with the same thickener concentration. Measurement of bearing torque was conducted for a deep-groove radial ball bearing by using a bearing test apparatus. The bearings filled with greases initially exhibited high torque but showed gradual decrease in the torque with prolonged rotation, where the greases with higher yield stress showed larger normalized torque decrease. Observation of bearing after the rotation revealed a tendency that the greases with larger normalized torque decrease had been pushed aside in the raceway by channeling. This implied that the greases with higher yield stress tended to show channeling. On the other hand, the greases with lower yield stress circulated within the bearing by churning and showed smaller normalized torque decrease. These behaviors were explained in terms of the yield stress of the greases and the shear stress to entrain the greases into the contacts. Observation of grease structure was made with atomic force microscopy showed that the greases whose thickener network structure was distributed more densely had higher yield stress.

Contribution of AFM Observations to the Understanding of Ni3Al Yield Stress Anomaly

2011 ◽  
Vol 61 ◽  
pp. 71-77
Author(s):  
Joël Bonneville ◽  
Dimitri Charrier ◽  
Christophe Coupeau
Keyword(s):  
Atomic Force Microscopy ◽  
Yield Stress ◽  
Intermetallic Compounds ◽  
Ordered Structure ◽  
Practical Situation ◽  
Force Microscopy ◽  
Atomic Force ◽  
Ni3al Intermetallic

We report in the present paper a practical situation where the use of atomic force microscopy allowed an irrefutable insight in material plasticity for discriminating between different modelling hypotheses concerning the yield stress anomaly of Ni3Al intermetallic compounds with the L12 ordered structure. The contribution of AFM to a better understanding of elementary rate controlling mechanisms as well as collective dislocation motions is highlighted.

scholarly journals Evaluations of All-in-One, Polycarboxylate-Based Superplasticizer with Viscosity Modifying Agents for the Application of Normal-Strength, High-Fluidity Concrete

2021 ◽  
Vol 11 (23) ◽  
pp. 11141
Author(s):  
Tae-Woong Kong ◽  
Hyun-Min Yang ◽  
Han-Seung Lee ◽  
Chang-Bok Yoon
Keyword(s):  
Compressive Strength ◽  
Rheological Properties ◽  
Yield Stress ◽  
Lower Yield ◽  
Lower Yield Stress ◽  
Slump Flow ◽  
Different Types ◽  
Long Time ◽  
Normal Strength ◽  
Physical Phenomena

High fluidity concrete exhibits an excellent self-compacting property. However, the application of typical high-fluidity concrete is limited in the normal strength range (18~35 MPa) due to the large amount of binder. Therefore, it is important to solve these problems by adding a viscosity modifying agent (VMA) with a superplasticizer (PCE), which helps to improve the fluidity of the concrete. In addition, the rheology and stability of the concrete with VMA can be improved by preventing bleeding and segregation issues. Current studies focused on the physical phenomena of concrete such as the fluidity, rheological properties, and compressive strength of normal-strength, high-fluidity concrete (NSHFC) with different types of a polycarboxylate-based superplasticizer (NPCE). The obtained results suggested that the combinations of all-in-one polycarboxylate-based superplasticizers (NPCE) did not cause any cohesion or sedimentation even stored for a long time. The combination of three types of VMA showed the best fluidity (initial slump flow of 595~630 mm) without any segregation and bleeding, and the compressive strength at 28 days was also found to be the highest: 34–37 MPa. From these results, the combination of PCE (2.0%) + HPMC (0.3%) + WG (0.1%) + ST (0.1%) showed an 18% higher plastic viscosity and -4.4% lower yield stress than Plain.

On the Propagation of Lu¨ders Bands in Steel Strips

2000 ◽  
Vol 67 (4) ◽  
pp. 645-654 ◽  
Author(s):  
S. Kyriakides ◽  
J. E. Miller
Keyword(s):  
Yield Stress ◽  
Strain Level ◽  
Finite Element Models ◽  
Localized Deformation ◽  
Lower Yield ◽  
Lower Yield Stress ◽  
Fine Grained ◽  
Steel Strips ◽  
Initiation And Propagation ◽  
Transient Events

The initiation and propagation of Lu¨ders-type localized deformation in thin, fine grained steel strips in tension is studied through combined experimental and analytical efforts. Purely elastic deformation is terminated (upper yield stress) by localized deformation which tends to initiate along preferred directions. The strain level associated with this material instability is limited to two to five percent. When this strain level is achieved locally, the instability propagates via inclined fronts which separate coexisting regions of essentially elastic and plastically deformed materials. Under displacement controlled stretching, one or two fronts propagate in a steady-state manner (lower yield stress). The propagation of one and two fronts are simulated numerically using finite element models in which the material is modeled as a finitely deforming elastoplastic solid with an up-down-up nominal stress-strain response. The simulations capture the major events observed in the experiments such as the initiation process, the propagation of inclined fronts, kinking of the strip and the build up of moments, and the periodic straightening and moment reduction through transient events. This confirms that structural effects play a major role in the evolution of observed events. [S0021-8936(00)01604-4]

The Yield Phenomena of a Medium Carbon Steel under Dynamic Loading

1949 ◽  
Vol 161 (1) ◽  
pp. 165-175 ◽  
Author(s):  
F. V. Warnock ◽  
D. B. C. Taylor
Keyword(s):  
Carbon Steel ◽  
Yield Stress ◽  
Testing Machine ◽  
Strain Curve ◽  
Medium Carbon Steel ◽  
Impact Testing ◽  
Lower Yield ◽  
Lower Yield Stress ◽  
Medium Carbon ◽  
True Shape

The paper describes dynamic tensile tests carried out on a medium carbon steel to determine the true shape of the stress-permanent strain curve for rapid straining. The variation of this curve with change in strain rate, and the progressive deformation of the steel are also studied. An impact testing machine was used, straining being carried out as a series of dynamic loadings, and the stress was measured by means of electrical resistance strain gauges attached directly to the specimens. Comparison is effected between dynamic and static stress-strain curves, the existence of a “dynamic upper yield stress” and a “dynamic lower yield stress” being shown, together with a difference in the rate of strain hardening for the two straining conditions. Non-uniform yielding of the metal is shown to be more pronounced for dynamic straining and, like static yielding, to be an integral part of the lower yield stress phenomenon. The manner in which all these factors are affected by normalizing the steel is shown. A special form of deformation of the steel peculiar to rapid straining is indicated. Theoretical and experimental facts are used to deduce a theory for the observed increases in stress, and the use of these dynamic stresses for design purposes is discussed.

Grease thixotropy: evaluation of grease microstructure change due to shear and relaxation

2014 ◽  
Vol 66 (2) ◽  
pp. 223-237 ◽  
Author(s):  
Maciej Paszkowski ◽  
Sylwia Olsztyńska-Janus
Keyword(s):  
Qualitative Assessment ◽  
Structural Components ◽  
Lubricating Grease ◽  
Content Type ◽  
Base Oil ◽  
Force Microscopy ◽  
Atomic Force ◽  
Physicochemical Interactions ◽  
Lithium Soap ◽  
Mineral Base

Purpose – The thixotropy of lubricating grease thickened with lithium 12-hydroxystearate with mineral base oil was investigated. The thixotropy has a significant influence on the flow resistance and pressure drop in the structural components of lubrication systems, which is of major importance as today the latter are being centralized and automated. The paper aims to discuss these issues. Design/methodology/approach – Rheometer studies on thixotropy were carried out and the grease microstructure was visualized using atomic force microscopy (AFM). Total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was used to study the physicochemical interactions which indicate the disintegration and recovery of the grease microstructure. Findings – A qualitative assessment of the physicochemical interactions between lithium soap floccules was made and a theory of the self-ordering effect of lithium 12-hydroxystearate associated molecules during shearing and their aggregation and flocculation during relaxation has been proposed. Originality/value – Because of the complexity of the disintegration and recovery of the lubricating grease thickener microstructure, there is still limited physical understanding of the mechanism of this process. Therefore, the present research was undertaken to identify the phenomena involved.

scholarly journals Performance test of cantilever transfer standard used for afm tip calibration based on electromagnetic compensation

ACTA IMEKO ◽  
2020 ◽  
Vol 9 (5) ◽  
pp. 129
Author(s):  
J. Jiang ◽  
H. Zhou ◽  
Y. Zhang ◽  
S. Wu ◽  
Z. Zhang ◽  
...  
Keyword(s):  
Atomic Force Microscopy ◽  
Performance Test ◽  
Test Apparatus ◽  
Relative Uncertainty ◽  
Transfer Standard ◽  
Force Microscopy ◽  
Stiffness Measurement ◽  
Calibration Test ◽  
Atomic Force

This paper describes stiffness measurement of cantilever transfer standards used for Atomic Force Microscopy (AFM) tip calibration based on electromagnetic compensation. The transfer standard of cantilever is designed and manufactured based on the bulk fabrication of SOI wafers. The measure range of the transfer standard covers from 0.04 N/m to 16 N/m. The series of transfer standard is designed for the calibration test of the cantilever used in AFM, along with the test apparatus specifically designed. The relative uncertainty of the stiffness is smaller than 2.4 % (<em>k</em> = 2).

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