Shear Stresses Imposed on Oils During Low-Temperature Starting

2009 ◽  
pp. 96-96-19 ◽  
Author(s):  
DL Alexander
Keyword(s):  
Low Temperature ◽  
Shear Stresses

scholarly journals Tangential forces in the contact area of upper road layer with the base

2018 ◽  
Vol 239 ◽  
pp. 05012 ◽  
Author(s):  
Timmo Gavrilov ◽  
Gennady Kolesnikov ◽  
Konstantin Khoroshilov
Keyword(s):  
Low Temperature ◽  
Contact Area ◽  
Piecewise Linear ◽  
Shear Stresses ◽  
Shear Forces ◽  
The Road ◽  
Concrete Layer ◽  
Order Polynomial ◽  
Low Temperature Cracking ◽  
Tangential Forces

Low-temperature cracking is one of the main reasons for the deterioration of the upper layer of roads in regions with cold winters. A large number of works focused on deterioration prevention are known, however the interdisciplinary problem of low-temperature cracking remains relevant. The important, but insufficiently studied factor is the distribution of normal and tangential (shear) forces acting on the upper layer of the road. The objective of the current study was to clarify insight about the distribution of tangential forces in the contact area of the upper layer of the road with the base. There are works in which it is assumed that these forces are distributed by a piecewise linear law. We propose a mechanical and mathematical model and an analytical solution to the problem of the distribution of shear forces in the contact area of the upper layer with the base. The main result of the study: it is found that the distribution of shear forces in the segment of the asphalt concrete layer is described by a second-order polynomial. However, the shear stresses are distributed linearly over the entire length of the segment and reach the highest modulo values in the area of the end sections of the segment. The results of the presented study clarify the understanding of functioning of the upper road layer at low temperatures. By that, the contribution to the solution of the problem of increasing the crack resistance of roads in regions with cold winters is made.

scholarly journals How Nanoscale Dislocation Reactions Govern Low- Temperature and High-Stress Creep of Ni-Base Single Crystal Superalloys

Crystals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 134 ◽  
Author(s):  
David Bürger ◽  
Antonin Dlouhý ◽  
Kyosuke Yoshimi ◽  
Gunther Eggeler
Keyword(s):  
Low Temperature ◽  
Single Crystal ◽  
High Stress ◽  
Shear Stresses ◽  
Creep Tests ◽  
Shear Creep ◽  
Tem Analysis ◽  
Transmission Electron ◽  
Crystallographic Shear ◽  
Shear System

The present work investigates γ-channel dislocation reactions, which govern low-temperature (T = 750 °C) and high-stress (resolved shear stress: 300 MPa) creep of Ni-base single crystal superalloys (SX). It is well known that two dislocation families with different b-vectors are required to form planar faults, which can shear the ordered γ’-phase. However, so far, no direct mechanical and microstructural evidence has been presented which clearly proves the importance of these reactions. In the mechanical part of the present work, we perform shear creep tests and we compare the deformation behavior of two macroscopic crystallographic shear systems [ 01 1 ¯ ] ( 111 ) and [ 11 2 ¯ ] ( 111 ) . These two shear systems share the same glide plane but differ in loading direction. The [ 11 2 ¯ ] ( 111 ) shear system, where the two dislocation families required to form a planar fault ribbon experience the same resolved shear stresses, deforms significantly faster than the [ 01 1 ¯ ] ( 111 ) shear system, where only one of the two required dislocation families is strongly promoted. Diffraction contrast transmission electron microscopy (TEM) analysis identifies the dislocation reactions, which rationalize this macroscopic behavior.

Yield Stress in Frozen Rubbers

1954 ◽  
Vol 27 (1) ◽  
pp. 104-119
Author(s):  
J. M. Buist ◽  
R. L. Stafford
Keyword(s):  
Low Temperature ◽  
Natural Rubber ◽  
Yield Stress ◽  
Shear Deformation ◽  
Applied Stress ◽  
Room Temperature ◽  
Large Temperature ◽  
Shear Stresses ◽  
Tension Tests ◽  
Deformation Properties

Abstract The work reported on the low temperature shear deformation properties of natural rubber and Neoprene-GN gum compounds shows that, under the conditions of storage and applied stress investigated, there is little evidence of a yield effect with Neoprene-GN. It is suggested that the very large temperature-stiffening of this polymer is too great to give the yield effect under the low shear stresses studied. In tension, however, the yield effect is very marked with Neoprene-GN. On the other hand, a definite yield effect is shown as a result of shear deformation measurements on natural rubber stored at −40° C, whereas previous tension tests failed to detect this. It is shown that, under suitable conditions of storage time and at high shearing stresses, a natural rubber unit might fail in service by yielding and giving too much deflection. The more usual type of failure of a shear unit in service arises from loss of flexibility and hence deflection properties; the oil-resisting rubbers are particularly likely to suffer from this defect. The x-ray data on natural rubber and Neoprene-GN gum compounds failed to reveal any evidence of random crystallite formation in the unstretched frozen rubbers. If the yield effect is due to crystallite formation in the unstretched state at low temperatures, then the crystallites are too small to be detected under the conditions of this investigation. In this connection, it is emphasized that a temperature of −40° C is below the temperature for maximum rate of development of crystallization for both rubbers. With both natural rubber and Neoprene-GN, crystallization resulting from stretching occurs more readily and at lower elongations at −40° C than at room temperature. In the case of Neoprene-GN stored at −40° C and then stretched, crystallization does not increase with elongation as it does at room temperature. It is suggested that this is due to the cold-drawn state of Neoprene-GN on stretching after storage at −40° C. These investigations have important practical and theoretical implications. Suggestions have often been made to include a test for crystallization in any characterization of compounds for low-temperature resistance. The results of the present work emphasize that the important factor is the time of storage at low temperature and the effects that this produces on crystallization and yield stress. The presence of crystallization is not so important as its continued development under long period exposure or its reorientation under applied stress.

The Application of Fuzzy-Ball Drilling Fluid to Deepwater Drilling to Deal With Highly Mineralized Formation Brines and Low-Temperature Environment

2018 ◽  
Author(s):  
Panfeng Wei ◽  
Lihui Zheng ◽  
Mingzheng Yang ◽  
Yuanhang Chen
Keyword(s):  
Low Temperature ◽  
Rheological Properties ◽  
Oil And Gas ◽  
High Salinity ◽  
Drilling Fluid ◽  
Experimental Studies ◽  
Field Tests ◽  
Shear Stresses ◽  
Deepwater Drilling ◽  
Temperature Environment

For deepwater oil and gas well drilling with the issue of highly mineralized formation brines, it is required that the drilling fluid properties are not affected by the high salinity formation fluid and the low-temperature environment. A novel drilling fluid mainly consists of fuzzy-ball fluid, which has an excellent tolerance to salinity and low temperature, has the potential to be applied for deepwater drilling to achieve safe and efficient drilling tasks. Experimental studies and field tests have been carried out to characterize the rheological properties of fuzzy-ball drilling fluid under different conditions of brine salinity and test temperature. In the experimental test, fuzzy-ball fluids with different densities are prepared with brines of varying salinity mineralized by Ca2+ and Mg2+. The rheological curves are plotted from different apparent viscosities and shear stresses under different shear rates measured by a rheometer under 10 ∼ 80°C and a six-speed viscometer at 0°C. The results positively showed that the yield stress of fuzzy-ball fluid is stable at a relatively high value with the variation of fluid salinity and temperature. The apparent viscosity slightly increases with the decrease of salinity and temperature. It can be claimed that the rheological properties of fuzzy-ball drilling fluid are stable within the range of salinity and temperature investigated experimentally. Field tests have been conducted during several workover jobs, the rheological properties of fuzzy-ball drilling fluid were stable at temperatures and salinities on site. Thus, it can be proved that the novel fuzzy-ball drilling fluid could be applied in deepwater drilling under the high salinity formation fluid and low-temperature environment.

Exsolution and inversion in pigeonite from the Whin Sill, Northern England

1978 ◽  
Vol 36 (1) ◽  
pp. 474-475
Author(s):  
P.P.K. Smith
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Homogeneous Nucleation ◽  
Silicate Mineral ◽  
Antiphase Boundaries ◽  
Two Phase ◽  
Primitive Form ◽  
The Core ◽  
Nucleation Mechanisms ◽  
And Inversion

Grains of pigeonite, a calcium-poor silicate mineral of the pyroxene group, from the Whin Sill dolerite have been ion-thinned and examined by TEM. The pigeonite is strongly zoned chemically from the composition Wo8En64FS28 in the core to Wo13En34FS53 at the rim. Two phase transformations have occurred during the cooling of this pigeonite:- exsolution of augite, a more calcic pyroxene, and inversion of the pigeonite from the high- temperature C face-centred form to the low-temperature primitive form, with the formation of antiphase boundaries (APB's). Different sequences of these exsolution and inversion reactions, together with different nucleation mechanisms of the augite, have created three distinct microstructures depending on the position in the grain.In the core of the grains small platelets of augite about 0.02μm thick have farmed parallel to the (001) plane (Fig. 1). These are thought to have exsolved by homogeneous nucleation. Subsequently the inversion of the pigeonite has led to the creation of APB's.

Low temperature x-ray microanalysis of frozen-hydrated tobacco leaves

1984 ◽  
Vol 42 ◽  
pp. 284-285
Author(s):  
S. Edith Taylor ◽  
Patrick Echlin ◽  
May McKoon ◽  
Thomas L. Hayes
Keyword(s):  
Low Temperature ◽  
Lemna Minor ◽  
Root Tips ◽  
Tobacco Leaves ◽  
X Ray ◽  
Whole Cells ◽  
Carbon Coated ◽  
The Right ◽  
Beam Currents ◽  
The University

Low temperature x-ray microanalysis (LTXM) of solid biological materials has been documented for Lemna minor L. root tips. This discussion will be limited to a demonstration of LTXM for measuring relative elemental distributions of P,S,Cl and K species within whole cells of tobacco leaves.Mature Wisconsin-38 tobacco was grown in the greenhouse at the University of California, Berkeley and picked daily from the mid-stalk position (leaf #9). The tissue was excised from the right of the mid rib and rapidly frozen in liquid nitrogen slush. It was then placed into an Amray biochamber and maintained at 103K. Fracture faces of the tissue were prepared and carbon-coated in the biochamber. The prepared sample was transferred from the biochamber to the Amray 1000A SEM equipped with a cold stage to maintain low temperatures at 103K. Analyses were performed using a tungsten source with accelerating voltages of 17.5 to 20 KV and beam currents from 1-2nA.

Bulk standards for low-temperature biological x-ray microanalysis

1984 ◽  
Vol 42 ◽  
pp. 282-283
Author(s):  
P. Echlin ◽  
M. McKoon ◽  
E.S. Taylor ◽  
C.E. Thomas ◽  
K.L. Maloney ◽  
...  
Keyword(s):  
Phase Separation ◽  
Low Temperature ◽  
Analytical Method ◽  
Salt Solutions ◽  
Absolute Concentration ◽  
Cooling Process ◽  
X Ray ◽  
The Absolute ◽  
Analytical Procedures ◽  
Electrical Conductors

Although sections of frozen salt solutions have been used as standards for x-ray microanalysis, such solutions are less useful when analysed in the bulk form. They are poor thermal and electrical conductors and severe phase separation occurs during the cooling process. Following a suggestion by Whitecross et al we have made up a series of salt solutions containing a small amount of graphite to improve the sample conductivity. In addition, we have incorporated a polymer to ensure the formation of microcrystalline ice and a consequent homogenity of salt dispersion within the frozen matrix. The mixtures have been used to standardize the analytical procedures applied to frozen hydrated bulk specimens based on the peak/background analytical method and to measure the absolute concentration of elements in developing roots.

Field ion microscopy

1988 ◽  
Vol 46 ◽  
pp. 434-435
Author(s):  
Gert Ehrlich
Keyword(s):  
Low Temperature ◽  
Sample Surface ◽  
Low Pressure ◽  
Radius Of Curvature ◽  
Field Ion Microscopy ◽  
Phosphor Screen ◽  
Ion Microscopy ◽  
Field Ion Microscope

The field ion microscope, devised by Erwin Muller in the 1950's, was the first instrument to depict the structure of surfaces in atomic detail. An FIM image of a (111) plane of tungsten (Fig.l) is typical of what can be done by this microscope: for this small plane, every atom, at a separation of 4.48Å from its neighbors in the plane, is revealed. The image of the plane is highly enlarged, as it is projected on a phosphor screen with a radius of curvature more than a million times that of the sample. Müller achieved the resolution necessary to reveal individual atoms by imaging with ions, accommodated to the object at a low temperature. The ions are created at the sample surface by ionization of an inert image gas (usually helium), present at a low pressure (< 1 mTorr). at fields on the order of 4V/Å.

High-Vacuum Evaporation and a Cryostage to Observe Fractured Yeast

1988 ◽  
Vol 46 ◽  
pp. 256-257
Author(s):  
William P. Wergin ◽  
Eric F. Erbe ◽  
Eugene L. Vigil
Keyword(s):  
Electron Microscope ◽  
Low Temperature ◽  
Standard Specimen ◽  
High Vacuum ◽  
Specimen Holder ◽  
Sputter Coating ◽  
Fresh Frozen ◽  
Gain Access ◽  
Scanning Electron ◽  
Transfer Device

Investigators have long realized the potential advantages of using a low temperature (LT) stage to examine fresh, frozen specimens in a scanning electron microscope (SEM). However, long working distances (W.D.), thick sputter coatings and surface contamination have prevented LTSEM from achieving results comparable to those from TEM freeze etch. To improve results, we recently modified techniques that involve a Hitachi S570 SEM, an Emscope SP2000 Sputter Cryo System and a Denton freeze etch unit. Because investigators have frequently utilized the fractured E face of the plasmalemma of yeast, this tissue was selected as a standard for comparison in the present study.In place of a standard specimen holder, a modified rivet was used to achieve a shorter W.D. (1 to -2 mm) and to gain access to the upper detector. However, the additional height afforded by the rivet, precluded use of the standard shroud on the Emscope specimen transfer device. Consequently, the sample became heavily contaminated (Fig. 1). A removable shroud was devised and used to reduce contamination (Fig. 2), but the specimen lacked clean fractured edges. This result suggested that low vacuum sputter coating was also limiting resolution.

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