Study On Fractal Prediction Of Running-in Wear In Connecting Rod Bushes-piston Pin Pair

Connecting rod bushes-piston pin pair is one of the important engine sliding friction pairs, whose operating reliability restrains the engine from developing into the direction of high speed and heavy load. The results show that wear is the main failure mode of connecting rod bushing. So the properties of friction and wear were researched to investigate the wear failure mechanism and find out the wear rules, which have a great engineering and practical significance in optimization of tribology performance in connecting rod bushed-piston pin friction pair.This paper first introduced the fractal theory and its applications in tribology research. Then through the fractal theory, the modified M-B fractal contact model of connecting rod bushes-piston pin pair was established, with the changes of contact state of the micro convex body divided into three contact deformation processes which respectively were plastic, elastic plastic, elastic process. And the critical micro contact cross-sectional area of three states transition and contact pressure of each state process were calculated. As to the fractal contact model, the relationship among real contact area and contact state, load, and the influence of contact area distribution on the contact state and elastic contact points were analyzed. What's more, the influence of contact state on the wear rate and the elastic contact area ratio were analyzed, with the findings that the optimum fractal dimension exists on the rough surface, resulting in minimum wear of the wear process and the shortest time of running-in.On the basis of running-in and wear test, the influence of different speed and different load on the wear of connecting rod bushes was studied, with the conclusion that the wear rate increases as speed and load respectively grows. Through the comparison of the inner surface morphology of the connecting rod bushes before and after running-in and wear, it is found that the main wear is adhesive one, which is companied with abrasive one. And then comparative analysis of several classic running-in and wear mathematical models was performed. Based on the fractal prediction model of the wear rate built by Zhou G Y, etc., with the coefficients of elastic contact wear and lubrication oil damages taken into consideration, the formula of mean wear depth rate was proposed, on the foundation of which, the change trend of mean wear depth rate with each variable and factor was briefly analyzed.The torque signal under the conditions of variable speed and load was calculated by the single fractal dimension. The number of each working condition dimension was calculated by box dimension. Then the effect of rotational speed and load on the friction torque is analyzed. Then the friction torque signal in the process of running-in under the conditions of constant speed and load was calculated by the multiple fractal dimensions and the multi-fractal spectrum was calculated. And analysis of the multi-fractal spectrum changes and its width and difference with time was performed. The research results indicate that the changes of the shape, width and difference of the multi-fractal spectrum can represent the change process of running-in and wear and predict the process of running-in and wear very well.