Currently, the increasing demand for smaller and more efficient systems is increasing the stress put on interacting components. This forces components to operate in the boundary lubrication regime. In this lubrication regime, the normal load put on the components is no longer carried by the lubricant but rather by the interacting asperities, and by doing so solid-solid contact is inevitable. This increases the specific wear seen in these types of systems shortening the lifetime of components and increasing maintenance intervals. This decreases the operational times significantly. Therefore, it is of great importance to get a clear understanding of the concept of corrosive wear under these specific conditions. In this thesis three different aspects of wear are discussed namely: the transition from mild to severe wear, running-in and the steady state mild wear. The first is modeled using a thermal threshold originating from Blok’s hypothesis that the transition to adhesive wear is caused by transcending a predefined critical temperature. The model discussed in the current work is based on a numerical thermal model combined with an elastic-plastic contact solver, which are both using the DC-FFT algorithms combined with CGM iterative schemes. In this way the model is able to incorporate mild wear into the thermal and contact calculations while keeping the computational times within a reasonable range. The model is validated through an experimentally determined transition diagram. Running-in of surfaces is modeled using the hypothesis that an additive rich oil is able to protect the contacting elements from metal to metal contact therefore, the growth rate should be the same or greater than the layer removal rate. This hypothesis is combined with a wear model based on a maximum equivalent strain assumption. This states that for material to be removed both an equivalent plastic strain threshold should be met and that the volume including this strain should reach the surface. To be able to compute the plastic strain, a Semi-Analytical-Contact solver is developed based on a local friction model. The mild wear model is based on the dynamic chemical balance at the surface. Through mechanical removal the balance is disturbed and the system will restore the balance through chemical reactions between the base material and additives present in the oil. Since the chemical reaction layers are very thin compared to contact regions, it can be assumed that it has only a limited effect on contact conditions. Using this hypothesis, a model is presented to determine the removal rate of the chemical reaction layer and thus the intensity of corrosive wear. The validation of this model is done using model systems. This thesis is divided into two parts: the first part is a summary of theory presented in the appended papers presented in the second part. This way the reader is able to keep a clear view on the overall goal of the research by reading the first part while the details are discussed in the second part.
|Qualification||Doctor of Philosophy|
|Award date||28 Jan 2011|
|Place of Publication||Enschede|
|Publication status||Published - 28 Jan 2011|