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- Isaksson, Ove
(author)
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Numerical analysis of elastohydrodynamic contacts using power-law lubricant with special reference to water-based hydraulic fluids
- 1987
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In: ASLE transactions. - : Informa UK Limited. - 0569-8197. ; 30:4, s. 501-507
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Journal article (peer-reviewed)abstract
- A numerical solution of the elastohydrodynamic lubrication problem for pure rolling with non-Newtonian lubricants is outlined. The non-Newtonian rheological model used is a modified power-law tau equals K multiplied by (times) gamma **n. At low shear rate gamma less than gamma //b, the lubricant is Newtonian, but when gamma greater than gamma //b the lubricant becomes non-Newtonian, tau equals K multiplied by (times) gamma **n. At high shear rate ( gamma yields infinity ) the lubricant becomes Newtonian again with the same viscosity as the base lubricant. By using this rheological model a modified Reynolds' equation is derived. The influence of the n-value and gamma //b on the film thickness has been investigated. Plots of the pressure distribution and film thickness within the contact for fluids with G-values in the range 169-986 is presented. These G-values are typical for water-based hydraulic fluids. For fluids with low n-values (n less than 0. 5) the pressure profile approaches the Hertzian pressure distribution and the minimum film thickness is that given by the base fluid viscosity.
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| 4. |
- Isaksson, Ove
(author)
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Rheology for water-based hydraulic fluids
- 1987
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In: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 115:1-2, s. 3-17
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Journal article (peer-reviewed)abstract
- High water-based hydraulic fluids with slightly higher viscosities than water, for instance 95-5 emulsions and micro-emulsions, do not show any significant deviation from a Newtonian fluid. Adding polymeric viscosity improvers for the purpose of increasing the viscosity will be successful as long as the shear rate is low. However, as the shear rate is increased, higher than about 10**3 s** minus **1, the viscosity will decrease and the advantage of the improver will vanish. The shear rate available was too low to break down the viscosity improvers. This is shown by the fact that the shear stress curve is reversible. Non-Newtonian fluids approach a more Newtonian behavior when the temperature is increased. The viscosity increase with pressure is much lower for water-based fluids than for a mineral oil. The pressure coefficient is about 10 times higher for mineral oils. The pressure coefficient increases if the water content of a water-based fluid is reduced.
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| 5. |
- Isaksson, Ove
(author)
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Rheology of jet fuel contaminated hydraulic fluid
- 1988
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Conference paper (peer-reviewed)abstract
- The viscosity at different pressures, temperatures and shear rates has been investigated. Furthermore, traction measurements between a steel ball and steel plate have been carried out. The results are compared with theoretical predictions. A decrease in oil film thickness due to viscosity loss has been established for fluids containing jet fuel. The pressure-viscosity-coefficient, the viscosity increase with pressure, is not effected by adding jet fuel to the hydraulic fluid.
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| 6. |
- Isaksson, Ove
(author)
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Water-based hydraulic fluids : rheology and elastohydrodynamic lubrication
- 1986
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Doctoral thesis (other academic/artistic)abstract
- Experiments have been carried out to measure traction, antiwear and rheological properties of water-based hydraulic fluids. Four types of fluids have been examined, emulsions, micro-emulsions, synthetic solutions and water-glycols. A numerical solution of the elastohydrodynamic lubrication problem for pure rolling with non-Newtonian lubricants is also outlined. The non-Newtonian rheological model used is a power-law, ... Non-Newtonian behaviour has been established for fluids with polymeric viscosity improvers. These non-Newtonian effects are less pronounced at high temperatures. The surface charge for emulsion droplets increases the viscosity considerably but on the other hand ionic contaminations decrease the viscosity. The viscosity increase with pressure is much lower for water-based fluids than for mineral oils. For fluids with low n-values (n < 0.5) the pressure profile in elastohydrodynamic contacts approaches the Hertzian pressure distribution and the minimum film thickness will be that given by the base fluid viscosity. The wear-rate is lowest for those fluids having the highest pressureviscosity coefficient along with a Newtonian behaviour. The water-glycols give low traction coefficients but will not prevent wear at high loads. There is a decrease in both wear rate and traction for emulsions having a less pronounced droplet stability. The same improvement is reached using micro-emulsions, with smaller droplets.
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| 7. |
- Lundberg, Jan
(author)
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Lubrication of a rotating ball in normal approach
- 1989
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In: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 130:1, s. 203-212
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Journal article (peer-reviewed)abstract
- An experimental study has been made of the degree of lubrication, which is defined as the number of interacting asperities, when a rotating spherical body approaches a plane during rotation. The normal velocity was varied between 0.1 and 0.5 m s-1 and the sliding velocity between 0 and 9.2 m s-1. The experiments show that the oil viscosity is the most important lubricant parameter. The degree of lubrication is not affected by either the normal velocity, the pressure viscosity coefficient or the shear strength proportionality constant. An increase in the sliding velocity gives a decrease in lubrication of between 25% and 65% depending on the surface roughness and type of lubricant. The surface roughness is also a most important factor impeding good lubrication. To avoid wear one has to increase the viscosity from 8 to 145 mm2 s-1 if the mean surface roughness Ra is increased from 0.01 to 0.14.
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| 9. |
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| 10. |
- Brewe, D.E., et al.
(author)
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Effect of vibration amplitude on vapor cavitation in journal bearings
- 1986
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In: Nordic Symposium on Tribology, Lulea, Sweden, 15-18 Jun. 1986. - Luleå : Högskolan i Luleå.
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Conference paper (peer-reviewed)abstract
- Computational movies were used to analyze the formation and collapse of vapor cavitation bubbles in a submerged journal bearing. The effect of vibration amplitude on vapor cavitation was studied for a journal undergoing circular whirl. The boundary conditions were implemented using Elrod's algorithm, which conserves mass flow through the cavitation bubble as well as through the oil-film region of the bearing. The vibration amplitudes for the different cases studied resulted in maximum eccentricity ratios ranging from 0.4 to 0.9. The minimum eccentricity ratio reached in each case was 0.1. For the least vibration amplitude studied in which the eccentricity ratio varied between 0.1 and 0.4, no vapor cavitation occurred. The largest vibration amplitude (i.e., eccentricity ratios of 0.1 to 0.9) resulted in vapor cavitation present 76 percent of one complete orbit.
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