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Purpose -This research investigated the mechanism of wet friction plates of engagement and solved the problem that the lock-up friction coefficient of sinter material could not be obtained but from experiments for a long time. The paper aims to discuss these issues. Design/methodology/approach -Including four steps: surface topology sampling and reconstruction, fractal parameters obtaining and fractal surface simulating, micro-contact mechanics model and friction coefficient fractal model, and experimental verification. Findings -After running in stage of the friction plates, the fractal dimension would reach a dynamically stable stage for a long time. The proportional coefficient K expresses the correlation between the base hardness and the asperities shear strength. The model could be property for one or more working condition via adjusting the coefficient K. The experiment data of friction coefficient are increased as the load magnified both in the model prediction and experiment practice. The trend is different from other models. Originality/value -This research is original and it is supported by national defense project. It would be served for tracked vehicles to solve the defect in transmission system. The friction coefficient is obtained via solving the tangential force in MB model. The surface topography could be reconstructed by laser topography instrument and the parameters could be received by program.

The effects of shot peening treatments on the microstructure and fatigue behavior of the teeth root in wet copper-based powder metallurgy friction plates were investigated and an efficient method for selecting optimal shot peening parameters for friction plates was proposed. Different experimental processes including microscopy observation, microhardness, roughness and X-ray diffraction measurements have been performed to characterize the treated surface of specimens. It is found that fatigue life of friction plates firstly increases and then decreases with the increase of Almen intensity, and the optimal fatigue life has improved over 55%. It is considered that both surface grain refinement and high residual compressive stress are the main ingredients responsible for the improved fatigue life. With further increase of Almen intensity, surface roughness of the teeth root gradually increases to a critical point, where rough peened surface may induce crack initiation due to stress concentration, and finally lead fatigue deteriorate.

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The material model was established by the finite element analysis software ABAQUS. The temperature field and stress field of iron-based powder metallurgy friction pairs under the brake pressure of 0.44Mpa and 0.8MPa were calculated respectively. The variation laws of temperature and stress under two pressure conditions were compared and analyzed. The results show that with the increase of braking pressure, the stress of the friction pairs increases, but the distribution of temperature and stress fields changes little.