Arthur J. Stipanovic

Theoretical and Experimental Studies of an Electro-Rheological Grease Shock Absorber

One method of achieving fail-safe, semi-active damping is to utilize a controllable fluid with a high zero-field damping capacity. To this end, this paper introduces a prototype electrorheological grease (ERG) as a new concept in electro-rheological fluids (ERFs). The general properties of grease-like fluids imply a non-Newtonian post yield viscosity. The fluid model developed in this paper considers the influence of a non-Newtonian post yield viscosity by using a power law model to account for shear thinning behavior. This model can be applied to all controllable fluids since it reduces to a Newtonian viscosity as a special case. The theoretical study includes a lumped parameter dynamic system model to predict the behavior of an actual damper, which takes into consideration inertial and compressibility effects. To validate the proposed models, a prototype damper was designed and used to collect data for a known ERF and the new ERG. Results from the ERG test data indicate that a good match between experimental and theoretical data was achieved. A sensitivity analysis shows that the model was insensitive to the mass of the fluid, but sensitive to the bulk modulus of the fluid. Comparisons are also made between the performance of the ERG and the existing ERF. The ERG demonstrates higher zero-electric field damping capacities than those of the ERF, yet produces an increase in damping when an electric field is applied.

The Impact of Crystalline Phase Morphology on the Water-Promoted Electrorheological Effect of Polysaccharides

Polysaccharides represent the world’s largest class of naturally occurring organic macromolecules and, as a result, potentially provide an excellent source of “particulate” materials for the design of electrorheological (ER) fluids. The ability of these polymers to exhibit an ER effect when dispersed in mineral, vegetable, or silicon oils has been well established1–3 although they generally require adsorbed water to promote activity which could limit their thermal range of useful application. As shown in Figure 1, typical polysaccharides contain glucose sugar monomeric residues which can interact readily with water via hydrogen bonding through a number of hydroxyl groups and ether oxygen atoms on the polymer.

Design and Performance of an Electro-Rheological Grease (ERG) Shock Absorber

The use of an electro-rheological fluid (ERF) in some applications may require a high damping capacity. This paper presents the design and evaluation of a prototype damper using an electro-rheological grease (ERG) with high zero electric field viscosity. In designing the ERG damper several issues such as: a) maintaining a constant internal damper volume, b) minimizing the fluid shear in flow paths (other than in the electrode gap region) which reduces adverse effects on damper performance and, c) allowing the adjustment of the electrode gaps, are considered. Comparisons are made between the performance of the ERG and an existing ERF. The ERG demonstrates higher damping capacities at low frequencies than those of the ERF.

Compositional analysis of re-refined and non-conventional lubricant base oils. Correlations to sequence VE and IIIE gasoline engine tests

In 1993, a Presidential Executive Order was issued requiring that federal agencies purchase lubricants containing at least 25% re-refined base oil. In light of this initiative, we have undertaken a program to characterize the chemical composition of re-refined base stocks, provided by a number of manufacturers, using column chromatography coupled with mass spectrometry techniques. The hydrocarbon-type distribution observed for the re-refined oils provides an index of their relative quality when benchmarked against conventionally processed `virgin` and certain non-conventional, high viscosity index (VI) base oils. Using statistical models which can predict lubricant performance in the ASTM Sequence VE and IIIE Gasoline Engine Tests from base oil compositional features and VI, it was determined that highly paraffinic synthetic and non-conventional base oils provide enhanced performance while re-refined oils generally exhibit predicted behavior comparable to an `average` `virgin` base oil, for most commercially available products. Sequence VE and IIIE test parameter predictions were found to be especially sensitive to the thioaromatic and multiring aromatic content of the base oil under evaluation. 11 refs., 5 figs., 6 tabs.

Evidence for microbial polysaccharide preparations containing polyester substituents

CPMAS 13C-n.m.r. spectroscopy was employed to characterize the composition and solid phase morphology of gellan, welan, rhamsan and NW11. Spectra indicated that commercial preparations of these polysaccharides, which share a similar molecular backbone, contain a non-carbohydrate component exhibiting four inequivalent carbon atoms. Isolation of this component, followed by 13C-n.m.r. in CHCl3 and MS analysis, revealed its structure to be poly(beta-hydroxybutyrate). Evidence is presented which suggests that this polyester may be a covalent adduct to the above polysaccharides, although this cannot be unambiguously determined at this time. Further experimentation is in progress.

Polysaccharides from Lichens: 13C-NMR Studies on (1–6) - Beta-D-Glucan (Pustulan)

The ubiquitous character of polysaccharides in nature provides the historical basis for the study and utilization of these renewable materials1–3. Considerable research has been focused on the chemical structure, molecular conformation, crystalline morphology, and physical properties of commercially important polysaccharides such as cellulose, starch, chitin, and xanthan gum while lesser attention has been directed to those carbohydrate-based polymers which serve as naturally occurring “specialty chemicals”. In the present study we have investigated the unique molecular properties of pustulan, a water-soluble, gel-forming polysaccharide produced by the lichen Umbilicaria papullosa (pustulata). Lichens are rather unusual organisms which represent a symbiotic relationship between a photosynthetic algae and a fungus which develops for the mutual benefit of both microorganisms in response to environmental stress such as dehydration4.