Rong Zhang
Published: 2011
Total Pages: 382
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The mechanism of surface damage known as scuffing has been a research topic of great interest for many years. However, the question of how scuffing is initiated and the factors that contribute to its occurrence are still poorly understood. Thermal analysis for scuffing will be very helpful to understand the mechanism of scuffing and explain some phenomena in scuffing. A two-dimensional rotational model and three-dimensional reciprocation model have been built to investigage the temperature distribution in scuffing phenomena. The numerical models are combined with a contact mechanics model to calculate the temperature distribution on the contact area during scuffing. The results showed that the local temperature before scuffing was high enough to change lubricant properties which will directly affect the scuffing process. However the temperature distribution was smooth even though the pressure distribution had many sharp peaks. The local temperature dropped to the ambient temperature very quickly when a contact area moved out of contact. However once scuffing occurred, the friction coefficient jumped to a high value generating more heat, the flash temperature could reach to 800° C which was high enough to change speciment's material properties. The three-dimensional reciprocation model had been utilized to investigate the domain and time effect on the validity of Jaeger and Carslaw theory. It was found that for a short time (Fourier number smaller than 1), Jaeger and Carslaw theory was valid for small calculation domain (L/l=4, H/l=2). However with increasing calculation time, a larger domain size was needed to ensure the accuracy of Jaeger and Carslaw theory. In order to investigage the scuffing mechanism, scuffing tests were conducted by using a high frequency testing rig. Low carbon steel specimens had the highest scuffing resistance as compared to medium and high carbon steel speciments. The martensite and tempered martensite stell had lower scuffing resistance but the wear resistance was much higher than the original material. For the martensite and tempered martensite, the scuffing resistance was very similar for each type of steel. After investigating the sub-surface of all speciments, plastic deformation was observed on all the testing speciments after scuffing. Hence plastic deformation is the main scuffing mechanism for the low, medium and high carbon steels.