Low cycle fatigue behavior of Ni-Nr lamellar eutectic composites at elevated temperatures

Low cycle fatigue properties of unidirectionally solidified lamellar eutectic Ni-51 Cr alloy were determined and compared with those of the cast microstructure in the temperature range of 300° to 760°C. Both materials exhibited an initial cyclic strain hardening followed by saturation over most of the temperature range. The rate and the amount of cyclic work-hardening decreased with temperature above 600°C. Rapid softening due to macro-crack propagation occurred at later stages of the fatigue process, which occupied an increasing portion of the fatigue life in the lamellar material as the strain amplitude was decreased. At Δ∈_T = 0.0190, the lamellar material exhibited longer fatigue life over the entire temperature range which has been related to the ability of Cr-rich lamellae to deflect fatigue cracks. At 625°C, the fatigue life (Nf) of both materials was related to the plastic strain range ( Δ∈_P) through the relationship (Δ∈_P/2 =K(2N_f)^c wherec andK are -0.39 and 0.068 for the lamellar, and -0.45 and 0.074 for the cast structure, respectively. At this temperature with decreasing strain amplitude lamellar material became more resistant to fatigue than as-cast structure, which has been related to the more efficient deflection of fatigue cracks by Cr-rich lamellae at lower strain amplitudes . Formerly with the Dept. of Metallurgical and Materials Engineering, University of Pittsburgh, Pittsburgh, Pa. Formerly Visiting Scientist, Department of Metallurgical and Materials Engineering, University of Pittsburgh Formerly Professor and Chairman, Department of Metallurgical and Materials Engineering, University of Pittsburgh     

Effect of SC-41930, a potent selective leukotriene B4 receptor antagonist, in the guinea pig model of middle ear inflammation

Arachidonic acid metabolites such as prostaglandins and leukotrienes have been shown to play an important role in the pathogenesis of otitis media (OM). Among these mediators, leukotriene B4 (LTB4) is one of the most potent inducers of inflammatory processes. SC-41930 has been shown to be a specific LTB4 receptor antagonist both in vitro and in vivo. In this study, anti-inflammatory effects of SC-41930 were investigated in a guinea pig model of OM induced by middle ear (ME) inoculation of killed Staphylococcus aureus. Outcome of treatment was determined by measurement of myeloperoxidase activity in the samples of ME mucosa, evaluation of temporal bone histopathology, and presence of ME fluids. Myeloperoxidase activity in the SC-41930-treated group was found to be significantly lower than that in the control group. Histopathology of temporal bones indicated decreased inflammation in the treated group as compared to the controls. In addition, ME fluids were absent in four out of six treated animals. These results demonstrate that SC-41930 can produce significant anti-inflammatory effects in this model of OM.     

Impact of necking and overlapping on radiative properties of coated soot aggregates

The impact of necking and overlapping on the radiative properties of coated soot aggregates was investigated numerically by using the Discrete Dipole Approximation (DDA). The present study concerns the situations of slight overlapping between primary particles and small to moderate necking. The effects of overlapping, necking, and coating on the aggregate volume equivalent radius were presented. To show the overlapping effect, the radiative properties of aggregates consisting of N = 200 particles were evaluated with and without coating at refractive indices of m = 1.60 + 0.60i for the soot core and m = 1.46 for the coating material at four different wavelengths in the visible and near-infrared. The radiative properties of coated soot aggregates with three overlapping values of 0.05, 0.1, and 0.2 were calculated. In addition, the relationship between absorption cross-section and wavelength was illustrated at overlapping values of 0.05, 0.1, and 0.2 for uncoated and 25%, 50%, 75%, and 100% coated aggregates. As overlapping and necking increased, the calculated extinction, absorption, and scattering properties also increased in the visible and near-infrared regions. It was found that the volume equivalent radii of coated aggregates increased linearly with coating thickness when the necking values were 0.40–0.50.

Copyright © 2017 American Association for Aerosol Research     

Deformation mechanisms in commercial Ti (0.5 at. pct oineq) at intermediate and high temperatures (0.3 - 0.6 tinm)

The plastic flow of the commercial titanium material Ti-50A (0.5 at. pct O_eq) of 22 μm grain size was investigated over the temperature range of 600 to 1150 structure) and strain rates of 3 x 10^-5 to 3 x 10^-2 per s employing both constant strain rate and strain rate cycling tests. Dynamic strain aging occurred in the temperature range of 600 to 850 (0.31 to 0.44T_m) with an activation energy of 50 kcal per mole derived from the start of serrations in the stress-strain curves, maxima in strain hardening and minima in ductility. This value is in accord with that for the diffusion of oxygen in titanium. At temperatures above 850 (0.46 to 0.59T_m) the data were very well represented by Weertman’s glide and climb high temperature creep mechanism, giving ε_skT/Dμb= 1.1 x 10⁶ (σ/μ)^4.55 withD = 1.0 x exp (- 57,800/RT). The value of 57.8 kcal per mole is in accord with available self-diffusion data for titanium.     

The sugars of honey—A review

Surveys of floral honey composition have established that the three major components are fructose, glucose, and water, averaging 38.2, 31.3 and 17.2%, respectively. Glucose and fructose are the only monosaccharides in honey and it is these sugars, combined in various forms, that comprise the di- and trisaccharide fractions of floral honey. Several laboratories, utilising various chemical and physical methods, have been responsible for the isolation and characterisation of ten disaccharides, ten trisaccharides, and two higher sugars from floral honey. Several of these occur only rarely in nature, and the trisaccharide erlose, produced by the action of honeybee invertase on sucrose, was first discovered as a component of honey. Honeydew honey is produced by the honeybee from honeydew deposits left by various hemipterous insects on their host plant. Honeydew contains a more complex mixture of sugars than does nectar, and honeydew honey is appreciably higher in reducing disaccharides and higher sugars than is floral honey. The trisaccharide melizitose, not found in floral honey, is often present in levels exceeding 10% in honeydew honey. The precipitation of glucose from honey, termed granulation, is often technologically undesirable as it is sometimes followed by fermentation. Indices such as the glucose/water ratio have been used to predict granulation tendency. Small amounts of hydroxymethylfurfural (HMF) occur naturally in honey, resulting from the acid catalysed dehydration of the hexoses, particularly fructose. High levels of HMF suggest adulteration of honey with acid inverted invert syrup and several methods are available for its determination. The conversion of nectar and honeydew to the complex array of honey sugars by the honeybee involves a variety of chemical and biochemical processes, some of which are now understood, while others remain to be elucidated.     

Grease Degradation in Rolling Element Bearings

Grease is degraded during use in rolling element bearings and as a result the lubrication performance can deteriorate. Under severe conditions this can result in lubrication failure and, thus, the grease life will effectively limit the bearing life. At present there is a lack of detailed information regarding the changes that occur in the grease and the way in which this degradation affects lubrication performance and failure.

This paper reports an initial study into grease degradation in bearings. The aim of the work was to characterize the changes that occur to the chemical and physical properties during use. A series of bearing tests using the modified DIN 51 806 test designated R2F(M) have been carried out using two greases: additized and non-additized. The tests have been run for different temperature and speed conditions for up to 300 hours. The aim was to examine the grease during normal running rather than after failure. At the end of the tests the bearings were dismantled and grease taken from different parts of the bearing for infrared spectroscopic analysis. This technique can characterize the degree of oxidation or degradation of the grease both in the bulk sample and from thin grease layers remaining on the bearing surfaces.

The analysis has shown that the condition of the grease varies depending on the distribution within the bearing. The lubricant remaining in the cage pocket region was heavily degraded and contained very little thickener. The grease on the seals contained different amounts of thickener depending on the seal position. The lubricant remaining on the inner raceway surface was predominately base oil although there was some thickener present. These results are discussed in the light of proposed bearing lubrication mechanisms.     

An application of Spectral line-based weighted sum of grey gases (SLW) model with geometric optics approximation for radiative heat transfer in 3-D participating media

A three-dimensional radiation code based on method of lines (MOL) solution of discrete ordinates method (DOM) coupled with spectral line-based weighted sum of grey gases (SLW) model and geometric optics approximation for particles is developed and its predictive ability is tested by applying it to the freeboard of a 0.3 MW_t Atmospheric Bubbling Fluidized Bed Combustor (ABFBC) containing a non-grey, absorbing, emitting and isotropically scattering particle laden flue gas and comparing its predictions with measurements and former predictions obtained by the grey gas model with Mie theory for particles. The MOL of DOM with SLW and geometric optics assumption are found to provide more accurate solutions for incident radiative heat flux than grey gas model with Mie theory particularly for high particle loading. Parametric studies are also carried out to investigate the effect of size parameter and presence of particles on fluxes. MOL–SLW predictions are found to be sensitive to both the size parameter and particle load.     

Evaluation of the boron tolerant grass, Puccinellia distans, as an initial vegetative cover for the Phytorestoration of a boron-contaminated mining site in Southern California

Land damaged by boron (B) mining should be restored to its natural state with a zero net impact on biodiversity. In an earlier study (Environ. Sci. Technol.2010,44, 7089-7095), we characterized a Turkish ecotype of the grass, Puccinellia distans, which exhibited extreme tolerance to B. Here we evaluated the use of a US ecotype of P. distans as an initial vegetative cover for the phytorestoration of a B mine in southern California. Hydroponic studies revealed that this P. distans ecotype tolerated B concentrations >100 mg B/L and could be germinated and grown in B-contaminated soils taken from the sites to be restored. P. distans grew well in moderately B-contaminated soil (～88 mg B/L saturated extract) amended with added organic matter (peat moss); other soil treatments such as gypsum addition or pH correction were not needed. P. distans also grew in severely B-contaminated soil (～1506 mg B/L) provided that toxic levels of soil B were diluted by the addition of sand and/or organic matter. Our results provide evidence in support of the concept of using the US ecotype of P. distans as an initial vegetative cover for the phytorestoration of B-contaminated soil.