Influence of the rheological behaviour of the lubricant on the appearance of pitting in elastohydrodynamic eegime

This paper analyses the influence of lubricant behaviour on the appearance of pitting. It attempts to study the effect of viscosity?pressure relation, compressibility, film thickness?roughness relation and friction coefficient on pitting failure of the contacting elements.To explain these effects, we first deal with the influence of the oil on the lubrication of the contact using elastohydrodynamic theory and secondly two multiaxial fatigue criteria are used, Crossland criterion and Dang Van criterion, to evaluate the influence of the rheology on the appearance of pitting. Finally, different applications are presented together with a discussion on the results obtained.

A rheological characterization of mashed potatoes enriched with soy protein isolate

The effect of the addition of soy protein isolate (SPI) (0, 15, 30, 45 and 60 g kg ) on viscoelastic properties, large deformation measurements and microstructure of fresh (FM) and frozen/thawed (F/TM) mashed potatoes was investigated. Rheological data showed weak gel behaviour for both FM and F/TM potatoes without and with added SPI together with a signi?cant decrease of system viscoelasticity (G and G ) with increasing SPI volume fraction, primarily attributed to the no interaction between the amylose/amylopectine matrix and the dispersed SPI particles or aggregates as revealed by scanning electron microscopy (SEM). Micrographs also showed that SPI formed white coarse aggregates. A freeze/thaw cycle produced a more signi?cant decrease in viscoelastic functions, due to superior aggregation of denatured SPI and reduced water activity. In F/TM samples, high correlations between small and large deformation measurements were found. Results may be useful for technological applications in SPI-enriched.

The influence of surfactant loading level in a montmorillonite on the thermal, mechanical and rheological properties of EVA nanocomposites

In this work, montmorillonite (Mt) has been organically modified with ethyl hexadecyl dimethyl ammonium (EHDDMA) in 20, 50, 80 and 100% of the nominal exchange capacity (CEC) of the Mt. A full characterization of the organo-montmorillonite (OMt) obtained has been made, including thermal analysis, X-Ray Diffraction, elemental analysis CHN and nitrogen adsorption. According to the results, 12% in mass of the surfactant added is strongly retained by the Mt. When the mass percentage of EHDDMA exchanged in the OMt is increased up to this level, the interactions OMt–EHDDMA are steeply reduced depending on the EHDDMA content. Clay polymer nanocomposites (CPN) were prepared by melt mixing of EVA and different loads of OMt. The CPN were compress molded to obtain 1 mm thick sheets, which have been characterized according to their mechanical, thermal and rheological behaviors. The major changes in the structure of the OMt are obtained for low contents of EHDDMA. Nevertheless, the CPN containing OMt exchanged at 20 and 50% of the CEC show relatively low effect of the EHDDMA while the mechanical response and rheological behavior of CPN with OMt modified at 80 and 100% of the CEC are much more pronounced.

Rheological properties of adhesives considered for interface damping

Mode of access: Internet.

Layered silicate nanocomposites based on various high-functionality epoxy resins. Part II: The influence of an organoclay on the rheological behavior of epoxy prepolymers

The effect of an organically surface modified layered silicate on the viscosity of various epoxy resins of different structures and different functionalities was investigated. Steady and dynamic shear viscosities of the epoxy resins containing 0-10 wt% of the organoclay were determined using parallel plate rheology. Viscosity results were compared with those achieved through addition of a commonly used micron-sized CaCO3 filler. It was found that changes in viscosities due to the different fillers were of the same order, since the layered silicate was only dispersed on a micron-sized scale in the monomer (prior to reaction), as indicated by X-ray diffraction measurements. Flow activation energies at a low frequency were determined and did not show any significant changes due to the addition of organoclay or CaCO3. Comparison between dynamic and steady shear experiments showed good agreement for low layered silicate concentrations below 7.5 wt%, i.e. the Cox-Merz rule can be applied. Deviations from the Cox-Merz rule appeared at and above 10 wt%, although such deviations were only slightly above experimental error. Most resin organoclay blends were well predicted by the Power Law model, only concentrations of 10 wt% and above requiring the Herschel-Buckley (yield stress) model to achieve better fits. Wide-angle X-ray measurements have shown that the epoxy resin swells the layered silicate with an increase in the interlayer distance of approximately 15 Angstrom, and that the rheology behavior is due to the lateral, micron-size of these swollen tactoids.

Friction factors and rheological behavior of Australian honey in a straight pipe

The pumping characteristics of four Australian honey samples were investigated in a straight pipe. Six flow rates (100-500 kg h(-1)) were studied at three temperatures (35-50degreesC). The pressure loss increased with an increase in the length of the pipe, as the low rate was increased and as the temperature was reduced. In the 25.4 mm-pipe, the Reynolds number ranged from 0.2-32.0 and are substantially less than the critica value (2040-2180) for laminar condition in the system. The relationship between the wall shear stress and shear rate approximated power-law behaviour, and the power-law index was not significantly (p>0.05) different from 1.0. The honey samples exhibited Newtonian behaviour at all the temperatures and this was confirmed by rheometric studies using Couette geometry. A friction chart was generated independent of temperature and the type of honey. An equation was developed to predict the pressure loss of the honey in a typical pipeline at any temperature once the viscosity-temperature relationship had been established.

Rheological Properties of Organoclay Suspensions in Epoxy Network Precursors

This paper deals with the evolution of the state of dispersion of organically modified montmorillonites in epoxy or amine precursors. The epoxy prepolymer is a diglycidyl ether of bisphenol A (DGEBA) and the curing agent is an aliphatic diamine with a polyoxypropylene backbone (Jeffamine D2000). The clay dispersion is evaluated at the platelet scale (nanoscopic scale) from X-ray spectrometry [wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS)] and at the aggregates scale (microscopic scale) from rheological analysis. The organoclays used form gels in the monomers above the percolation threshold if no shear is applied and present a mechanical gel/sol transition when shear stress increases. Gel strength and viscosity at high shear rates are linked to the nanometric state of dispersion and reveal the existence of two different organizations depending on organoclay/monomer interactions: (i) When the clay shows good interactions with the monomer, a significant swelling of the clay galleries by the monomer is obtained. These swollen particles lead to formation of weak gels which after shearing give high relative viscosity fluids. (ii) When the clay develops poor interactions with the monomer, the clay tends to reduce its exchange surface with the monomer and leads to a strongly connected gel. Shear breaks down this physical network leading to a very low relative viscosity fluid composed of nonswollen particles keeping a high aspect ratio. (C) 2003 Elsevier B.V All rights reserved.

A rheological assessment of the effect of trace level Ni additions on the solidification of Sn-0.7Cu

The influence of trace level Ni additions on the eutectic solidification mode of Sn-0.7Cu has been studied using continuous torque experiments during solidification. The solid fraction at which resistance to paddle rotation at the thermal centre of the sample occurs is related to the spatial distribution of solid during solidification. The results indicate that a transition in solidification mode occurs in the range 0-300 ppm Ni. Growth occurs antiparallel to heat flow from near the mould walls in the Ni-free alloy, while equiaxed growth from distributed centres dominates in alloys containing at least 300 ppm Ni. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Analysis of White Latex Paints using Laser Induced Breakdown Spectroscopy for Forensic Applications

The analysis of white latex paint is a problem for forensic laboratories because of difficulty in differentiation between samples. Current methods provide limited information that is not suitable for discrimination. Elemental analysis of white latex paints has resulted in 99% discriminating power when using LA-ICP-MS; however, mass spectrometers can be prohibitively expensive and require a skilled operator. A quick, inexpensive, effective method is needed for the differentiation of white latex paints. In this study, LIBS is used to analyze 24 white latex paint samples. LIBS is fast, easy to operate, and has a low cost. Results show that 98.1% of variation can be accounted for via principle component analysis, while Tukey pairwise comparisons differentiated 95.6% with potassium as the elemental ratio, showing that the discrimination capabilities of LIBS are comparable to those of LA-ICP-MS. Due to the many advantages of LIBS, this instrument should be considered a necessity for forensic laboratories.

Rheological Characterization of Bitumen and Asphalt including the effect of Added-recycled Material

This thesis evaluates the rheological behaviour of asphalt mixtures and the corresponding extracted binders from the mixtures containing different amounts of Reclaimed Asphalt (RA). Generally, the use of RA is limited to certain amounts. The study materials are Stone Mastic Asphalts including a control sample with 0% RA, and other samples with RA rates of 30%, 60% and 100%. Another set of studied mixtures are Asphalt Concretes (AC) types with again a control mix having 0% RA rate and the other mixtures designs containing 30%, 60% and 90% of reclaimed asphalt which also contain additives. In addition to the bitumen samples extracted from asphalt mixes, there are bitumen samples directly extracted from the original RA. To characterize the viscoelastic behaviour of the binders, Dynamic Shear Rheometer (DSR) tests were conducted on bitumen specimens. The resulting influence of the RA content in the bituminous binders are illustrated through master curves, black diagrams and Cole-Cole plots with regressing these experimental data by the application of the analogical 2S2P1D and the analytical CA model. The advantage of the CA model is in its limited number of parameters and thus is a simple model to use. The 2S2P1D model is an analogical rheological model for the prediction of the linear viscoelastic properties of both asphalt binders and mixtures. In order to study the influence of RA on mixtures, the Indirect Tensile Test (ITT) has been conducted. The master curves of different mixture samples are evaluated by regressing the test data points to a sigmoidal function and subsequently by comparing the master curves, the influence of RA materials is studied. The thesis also focusses on the applicability and also differences of CA model and 2S2P1D model for bitumen samples and the sigmoid function for the mixtures and presents the influence of the RA rate on the investigated model parameters.