Rolling-element fatigue life of AMS 5749 corrosion resistant, high temperature bearing steel

The rolling element fatigue lives of AMS 5749 and AISI M-50 were compared in tests run in the five ball fatigue tester and the rolling contact fatigue tester. The effects of double vacuum melting and retained austenite on the life of AMS 5749 were determined in five ball fatigue tests. The double vacuum melting process consisted of induction vacuum melting followed by vacuum arc remelting (VIM-VAR). In the five ball tests, VIM-VAR AMS 5749 gave lives at least six times that of VIM-VAR AISI M-50. Similar tests in the rolling contact fatigue tester showed no significant difference in the lives of the two materials. The rolling element fatigue life of VIM-VAR AMS 5749 was at least 14 times that of vacuum induction melted AMS 5749. A trend toward increased rolling element fatigue life with decreased retained austenite is apparent, but the confidence that all experimental differences are significant is not great

Effect of double vacuum melting and retained austenite on rolling-element fatigue life of AMS 5749 bearing steel

AMS 5749 steel combines the tempering, hot hardness, and hardness retention characteristics of AISI M-50 steel with the corrosion and oxidation resistance of AISI 440C stainless steel. The five-ball fatigue tester was used to evaluate the rolling-element fatigue life of AMS 5749. Double vacuum melting (vacuum induction melting plus vacuum arc remelting, VIM-VAR) produced AMS 5749 material with a rolling-element fatigue life at least 14 times that of vacuum induction melting alone. The VIM-VAR AMS 5749 steel balls gave lives from 6 to 12 times greater than VIM-VAR AISI M-50 steel balls. The highest level of retained austenite, 14.6 percent, was significantly detrimental to rolling-element fatigue life relative to the intermediate level of 11.1 percent

Towards an understanding of thermodynamic and kinetic controls on the formation of clay minerals from volcanic glass under various environmental conditions

lmogolite is the kinetically and thermodynamically favoured weathering product from rhyolitic volcanic glass in the soil-forming environment. However, on thermodynamic grounds imogolite would also appear to be the favoured alteration product of rhyolitic glass deposited in the nearshore marine environment. On the basis that the rate of conversion of glass to clay minerals is a function of the solubility of the clay mineral, smectite is expected to be formed under mildly diagenetic conditions, and formed more rapidly than imogolite in soil. The derived activation energies for formation of imogolite from glass in soils are appropriate for a diffusion controlled reaction, and appear consistent with the diffusion of the tetrahedrally co-ordinated species Al[iv](OH)₂(H2Q)⁺. In the marine environment, however the mechanism for all reactions appear to be surface reaction control

Aerodynamics of lift fan V/STOL aircraft

Aerodynamic characteristics of lift fan installation for direct lift V/STOL aircraf

Intestinal stem cell dynamics: a story of mice and humans

Stem cell dynamics define the probability of accumulating mutations within the intestinal epithelium. In this issue of Cell Stem Cell, Nicholson et al. (2018) report that human intestinal stem cell dynamics differ significantly from those of mice and establish that oncogenic mutations are more likely to expand; therefore, "normal" epithelium may carry multiple mutations

Process-structure-property relationships of additively manufactured model sandstone

The additive manufacturing of sand-based composites has primarily seen applications in the metal casting industry to offer improved ability to prepare complex molds. The weak bonding between sand grains, afforded by a thermosetting polymer, offers easy mold knock-out and sand recycling (see Figure 1). Our work involves rethinking binder-jetting technology in order to re-task the end application – making model sandstone to perform geotechnical analysis of rock formations. A major goal of the work is to be able to quantify the material properties of the binder phase (a thermosetting acid-catalyzed polymeric resin) which can then be input into particle flow code simulations to predict geomechanical responses of rock formations. The additive manufacturing process, its limitations, and modifications we have made to improve mechanical response of composites will be explained in the context of performance relative to natural sandstone. In particular, we will demonstrate that failure analysis of fractured composites and identification of failure modes led us to innovate the use of silane coupling agents to improve adhesion, and resulted in a two-fold improvement in unconfined compressive strength. In addition, we will detail our efforts to measure elastic moduli of binder necks between individual sand grains, and model the stiffness parameters required for use in computer simulations for macroscopic mechanical responses. With this work, the aim is to be able to representatively print model sandstone in large statistical sample sizes to study fluid flow through simulated formations, effects of defects on mechanical and fluid flow behavior, and predict behavior knowing material properties of the constituent materials. Please click Additional Files below to see the full abstract

Test virtuel d'un code de régulation DSP pour réseaux et systèmes d'entraînements électriques

Cet article décrit une procédure pour tester un code destiné à un DSP prévu pour le contrôle- commande d’équipements industriels tels que les systèmes d’entraînements à vitesse variable ou les réseaux électriques. Cette procédure repose sur le logiciel SIMSENTM développé à l’EPFL lequel offre nouvellement la possibilité de traduire une stratégie de contrôle-commande non plus impérativement à l’aide d’un schéma-bloc de réglage, mais également au travers du code défini par l’utilisateur et destiné à être implémenté. Ce code doit simplement être compatible avec le DSP choisi pour l’application prévue (code C, assembler, pascal, fortran,...), il se substitue au schéma-bloc. Il est ainsi possible de procéder aux tests et à l’optimisation des performances de l’ensemble d’un équipement. Dès lors que cette étape est résolue, il suffit de procéder au « download » du code établi dans le DSP de l’équipement. Cette procédure est non seulement une aide précieuse à une conception optimisée, elle permet des tests sans aucun risque ni limitations et induit des économies substantielles par le gain de temps qu’elle génère