The Mechanism Of The Effect Of Groove-textured Surface On The Friction-induced Vibration And Noise

Friction-induced vibration and noise has a strong influence on the precision and reliability of many mechanical systems, which has been considered as a serious problem and pollution for modern industry and living. Surface topography is considered to play a key role in the generation of squeal instability, and many studies have been devoted to the effect of surface topography (roughness, asperities, wear debris, etc) on the characteristic of friction noise. Recently, surface texture has been proved to have a significant influence on the tibological properties. However, there is very limited information in the literature on studying the relationship between friction noise and surface texture. Therefore, it is interesting to investigate the effect mechanism of surface texture on the friction-induced vibration and noise properties, which can lead to the specification of optimized surface texturing for reducing squeal.In this work, groove-textured surfaces with different sizes were manufactured on the compacted graphite iron specimens cut from the brake discs of a train. An experimental study on the difference between the groove-textured and original smooth surfaces in friction noise properties was performed. Subsequently, a numerical study was conducted to simulate the experimental process. Based on both the experimental and numerical results, the effect mechanism of groove-textured surface on friction-induced vibration and noise was discussed. The main conclusions can be drawn as following:1. Experimental results showed that when there were strong oscillations for both the friction force and vibration signals, the friction system became unstable and generated squeal. Groove-textured surfaces were found to have a significant influence on the friction-induced vibration and noise properties. The groove-textured surfaces with a specific dimensional parameter (T-500-250) showed good potential in reducing and suppressing squeal in the experimental test.2. No squeal generated on all the three surfaces (original smooth surfaces and T-500-125and T-500-250groove-textured surfaces) in the initial stage of tribological test, and about8cycles of wave-like fluctuations could be found in the friction force curves for the two groove-textured surfaces within half cycle, corresponding to the number of grooves within the sliding travel of4mm. In the steady stage, the squeal level of the specimens with a T-500-125groove-textured surface significantly increased, and the groove edges of T-500-125was smoothed by repeated impact with increasing number of cycles. In contrast, for T-500-250groove-textured surface,8cycles of wave-like fluctuations could still be observed within the half cycle of the friction force curve, and the groove edges of the T-500-250surface remained nearly unaffected despite wear. Therefore, the wave-like fluctuations of the friction force caused by ball sliding across the grooves is thought to play a crucial role in suppressing the generation of continuous high-frequency fluctuations of friction force and consequently the generation of squeal.3. A numerical study was conducted by using ABAQUS, to investigate the dynamic behavior of ball-on-smooth surface, ball-on-groove system and ball-on-groove textured surface with filleted edges configurations, respectively. Complex eigenvalue analysis was used to validate the model created by the finite element software, and the dynamic transient analysis was used to investigate the evolution of squeal vibration in the time domain. Based on both the experimental and numerical results, it can be concluded that the existence of impact between the edge and the ball counterface may cause wave-like fluctuations of friction force, which would disrupt the self-excited vibration of the friction system and suppress the generation of continuous high-frequency fluctuations of friction force and consequently the generation of squeal.4. A self-excited vibration model with three degrees of freedom was proposed to simulate the dynamic characteristic of ball sliding on groove textured surface and study the effect of inclined contact angle on system stability. The simulation results showed that the inclined contact angle had a significant effect on the generation of unstable vibration, and a lower angle would not cause the instability of friction system. The results supporting the hypothesis of the role of the discontinuous contact created by the textured surfaces:the low inclined contact angle (the diameter of counterface ball is much larger than the width of groove) in this investigation would not cause any continuous strong impact and instability of the system during the sliding process, instead, the impact would disrupt the self-excited vibration of the friction system and suppress squeal.5. Transient dynamic analysis (ABAQUS/Explicit) was conducted to investigate the interface dynamics when the friction system became unstable and generated squeal. The results showed that slave nodes were not in continuous contact with the master surface when self-excited vibration occurred. The contact between slave nodes and master surface in a relative motion has a characteristic of stick-slip-separation-stick. In addition, a self-excited vibration model with two degrees of freedom which based on the model of ball-on-smooth surface configuration was created, to investigate the effect of contact stiffness on friction-induced vibration and noise. It was found that the contact stiffness had a significant effect on friction noise, and friction system showed a stronger tendency to generate unstable vibration with a relatively higher ratio between the tangential and normal contact stiffness.