Details
| Originalsprache | Englisch |
|---|---|
| Qualifikation | Doktor der Ingenieurwissenschaften |
| Gradverleihende Hochschule | |
| Betreut von |
|
| Datum der Verleihung des Grades | 26 Apr. 2018 |
| Erscheinungsort | Hannover |
| Publikationsstatus | Veröffentlicht - 26 Feb. 2018 |
Abstract
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Hannover, 2018. 133 S.
Publikation: Qualifikations-/Studienabschlussarbeit › Dissertation
}
TY - BOOK
T1 - Traction in EHL-Contacts
T2 - the influence of local fluid rheology and temperatures
AU - Bader, N.
N1 - Doctoral thesis
PY - 2018/2/26
Y1 - 2018/2/26
N2 - The traction in concentrated contacts is governed by the fluid rheology. While the film formation has been well understood and its relation to the physical lubricant properties have been shown, the rheology governing the lubricant behaviour within elastohydrodynamic lubricated (EHL) contacts still poses numerous challenges. The limit of the traction transferable through a concentrated contact is governed by the lubricant property limiting shear stress. The behaviour of the limiting shear stress is evaluated by examining data from traction experiments. It is found that a linear relationship of pressure and maximum shear stress exists. The problem of using an integral contact is addressed by using data gained from a specialised experiment with homogeneous pressure. This shows the same pressure limiting shear stress relation. Thus the traction experiments are assumed a valid basis for extracting pressure limiting shear stress data. From the observations in the experiments a limiting shear stress relation is formulated and abstracted for several lubricants. This relation is subsequently implemented in a computational routine. The temperature dependence of the limiting shear stress is investigated by measurements of body temperature and by obtaining temperature maps of the contact through thermography. It can be found, that a small temperature dependence of the limiting shear stress may be present. However, when including the temperature maps into computations it is shown that the effect of temperature on viscosity out- weighs possible influences of temperature on the limiting shear stress. Furthermore, the knowledge of local temperatures makes the solution of the energy equation for a local temperature calculation unnecessary thus allowing for faster computations with the real temperat- ures. This is backed further by implementing several different viscosity models which are all based on identical high pressure viscometry data. It can be shown that the viscosity model influences the traction results substantially. Thus this work aims to achieve the following goals: Shed light on the true fluid behaviour in the EHL contact, point out the influence of temperature on the limiting shear stress, and further enhance a simple numerical model of the limiting shear stress for use in computations.
AB - The traction in concentrated contacts is governed by the fluid rheology. While the film formation has been well understood and its relation to the physical lubricant properties have been shown, the rheology governing the lubricant behaviour within elastohydrodynamic lubricated (EHL) contacts still poses numerous challenges. The limit of the traction transferable through a concentrated contact is governed by the lubricant property limiting shear stress. The behaviour of the limiting shear stress is evaluated by examining data from traction experiments. It is found that a linear relationship of pressure and maximum shear stress exists. The problem of using an integral contact is addressed by using data gained from a specialised experiment with homogeneous pressure. This shows the same pressure limiting shear stress relation. Thus the traction experiments are assumed a valid basis for extracting pressure limiting shear stress data. From the observations in the experiments a limiting shear stress relation is formulated and abstracted for several lubricants. This relation is subsequently implemented in a computational routine. The temperature dependence of the limiting shear stress is investigated by measurements of body temperature and by obtaining temperature maps of the contact through thermography. It can be found, that a small temperature dependence of the limiting shear stress may be present. However, when including the temperature maps into computations it is shown that the effect of temperature on viscosity out- weighs possible influences of temperature on the limiting shear stress. Furthermore, the knowledge of local temperatures makes the solution of the energy equation for a local temperature calculation unnecessary thus allowing for faster computations with the real temperat- ures. This is backed further by implementing several different viscosity models which are all based on identical high pressure viscometry data. It can be shown that the viscosity model influences the traction results substantially. Thus this work aims to achieve the following goals: Shed light on the true fluid behaviour in the EHL contact, point out the influence of temperature on the limiting shear stress, and further enhance a simple numerical model of the limiting shear stress for use in computations.
U2 - 10.15488/4459
DO - 10.15488/4459
M3 - Doctoral thesis
CY - Hannover
ER -