Effect of viscosity on rolling-element fatigue life at cryogenic temperature with fluorinated ether lubricants

Rolling-element fatigue tests were conducted with 12.7-mm-(1/2-in.-) diameter AISI 52100 steel balls in the NASA five-ball fatigue tester, with a maximum hertz stress of 5500 mN/m2 (800 000 psi), a shaft speed of 4750 rpm, lubricant temperature of 200 K (360 R), a contact angle of 20 deg, using four fluorinated ether lubricants of varying viscosities. No statistically significant differences in rolling-element fatigue life occurred using the four viscosity levels. Elastohydrodynamic calculations indicate that values of the lubricant film parameter were approximately 2 or greater

Study of hot hardness characteristics of tool steels

Hardness measurements of tool steel materials in electric furnace at elevated temperatures and low oxygen environment are discussed. Development of equation to predict short term hardness as function of intial room temperature hardness of steel is reported. Types of steel involved in the process are identified

Common bearing material has highest fatigue life at moderate temperature

AISI 52100, a high carbon chromium steel, has the longest fatigue life of eight bearing materials tested. Fatigue lives of the other materials ranged from 7 to 78 percent of the fatigue life of AISI 52100 at a temperature of 340 K (150 F)

Liquid cryogenic lubricant

Fluorinated polyethers are suitable lubricants for rolling-element bearings in cryogenic systems. Lubrication effectiveness is comparable to that of super-refined mineral oil lubricants operating at room temperature

Self-propulsion of a catalytically active particle near a planar wall: from reflection to sliding and hovering

Micron-sized particles moving through solution in response to self-generated chemical gradients serve as model systems for studying active matter. Their far-reaching potential applications will require the particles to sense and respond to their local environment in a robust manner. The self-generated hydrodynamic and chemical fields, which induce particle motion, probe and are modified by that very environment, including confining boundaries. Focusing on a catalytically active Janus particle as a paradigmatic example, we predict that near a hard planar wall such a particle exhibits several scenarios of motion: reflection from the wall, motion at a steady-state orientation and height above the wall, or motionless, steady "hovering." Concerning the steady states, the height and the orientation are determined both by the proportion of catalyst coverage and the interactions of the solutes with the different "faces" of the particle. Accordingly, we propose that a desired behavior can be selected by tuning these parameters via a judicious design of the particle surface chemistry

Flexural fatigue of hollow rolling elements

Hollow cylindrical bars were tested in the rolling-contact fatigue tester to determine the effects of material and outside diameter to inside diameter (OD/ID) ratios of 2.0, 1.6, 1.4, and 1.2 on fatigue failure mode and subsequent failure propagation. The range of applied loads with these OD/ID ratios resulted in maximum tangential tensile stresses ranging from 165 to 655 megapascals (24,000 to 95,000 psi) at the bore surface. Flexural failures of the hollow test bars occurred when this bore stress was 490 megapascals (71,000 psi) or greater with AISI 52100 hollow bars and 338 megapascals (49,000 psi) or greater with AISI M-50 hollow bars. Good correlation was obtained in relating the failures of these hollow bars with flexural failures of drilled balls from previously published full scale bearing tests

Short-term hot hardness characteristics of rolling-element steels

Short-term hot hardness studies were performed with five vacuum-melted steels at temperatures from 294 to 887 K (70 to 1140 F). Based upon a minimum Rockwell C hardness of 58, the temperature limitation on all materials studied was dependent on the initial room temperature hardness and the tempering temperature of each material. For the same room temperature hardness, the short-term hot hardness characteristics were identical and independent of material composition. An equation was developed to predict the short-term hardness at temperature as a function of initial room temperature hardness for AISI 52100, as well as the high-speed tool steels

Low-frequency noise reduction of spacecraft structures

Low frequency noise reduction of spacecraft structure

Effective squirmer models for self-phoretic chemically active spherical colloids

Various aspects of self-motility of chemically active colloids in Newtonian fluids can be captured by simple models for their chemical activity plus a phoretic slip hydrodynamic boundary condition on their surface. For particles of simple shapes (e.g., spheres) -- as employed in many experimental studies -- which move at very low Reynolds numbers in an unbounded fluid, such models of chemically active particles effectively map onto the well studied so-called hydrodynamic squirmers [S. Michelin and E. Lauga, J. Fluid Mech. \textbf{747}, 572 (2014)]. Accordingly, intuitively appealing analogies of "pusher/puller/neutral" squirmers arise naturally. Within the framework of self-diffusiophoresis we illustrate the above mentioned mapping and the corresponding flows in an unbounded fluid for a number of choices of the activity function (i.e., the spatial distribution and the type of chemical reactions across the surface of the particle). We use the central collision of two active particles as a simple, paradigmatic case for demonstrating that in the presence of other particles or boundaries the behavior of chemically active colloids may be \textit{qualitatively} different, even in the far field, from the one exhibited by the corresponding "effective squirmer", obtained from the mapping in an unbounded fluid. This emphasizes that understanding the collective behavior and the dynamics under geometrical confinement of chemically active particles necessarily requires to explicitly account for the dependence of the hydrodynamic interactions on the distribution of chemical species resulting from the activity of the particles.Comment: 26 pages, 11 figure