الفهرس | Only 14 pages are availabe for public view |
Abstract The effect of surface crack on the wear of polyamide 66 sliding against steel counterface in dry and wet conditions was investigated in pin-on-plate reciprocating testing machine. The test rig was designed to perform wear tests under constant and fluctuating loading conditions at constant sliding speed. Effects of crack orientation, under different static and cyclic loading parameters, on wear behaviour were examined. Relative change in wear rate due to surface crack existence, as well as crack orientation, was studied to provide understanding of surface fatigue wear. Results of the present study provide a basis for assessing the fatigue wear resulting during the primary stage from pre-existing surface crack defect. Under dry sliding, there was consistent evidence of the effect of surface crack on the wear rate under both loading conditions. A single transverse crack on the rubbing surface resulting in sever wear rate specially during running-in period. Surface crack may change the topography and the conformity of the polymer which, in turn, affect the characteristics of the formed transferred layer. The effect of surface crack on the transfer film formation was not limited to the existence of surface crack during the initial stage of wear. It was extended to the steady state stage of wear even the crack becomes worn out. Polymer wear showed a higher sensitivity to surface crack under cyclic loading rather than static loading. The correlation between running-in wear and pre-existing surface cracks explained as a process of ”sever” or ”progressive” surface fatigue wear. Polymer in dry sliding seems to be more sensitive to surface cracks than in water lubricated condition. Under wet sliding, the polymer showed generally higher wear rates compared to dry tests. However, wear process was ruled by the mechanical microploughing and abrasive wear mechanisms which showed minor sensitivity to surface crack. Plasticization, swelling and softening of the polymer were determining the effect of water lubricant on the wear behaviour. A mode of the wear of surface cracked polymer was designed to study the feasibility of neural network model that simulate the wear of polyamide under different working conditions, such as applied load, number of surface cracks and sliding conditions, using neural network application. The NNs showed good accuracy for the simulation and acceptable predicted values of wear rates were obtained. The NN is superior in both training time and accuracy and may be the solution for the cases including more input parameters such as the dimension and shape of the crack. Keywords: Wear, Polyamide, surface crack, Cyclic Load. |