The Self-adaptive Grinding Behaviours of High-speed Rail Grinding under the Sliding-rolling Composite Motions

The self-adaptive grinding behaviors of high-speed rail under sliding-rolling composite motions focused on optimizing grinding performance and surface quality. High-speed railways, characterized by high operational speeds and light axle loads, often suffer from rolling contact fatigue [1], which leads to surface spalling [2-4], fatigue cracks [5,6], and fractures [7,8]. These issues necessitate timely maintenance to ensure the safe and reliable operation of rail networks. Traditional rail grinding techniques aim to address deep-seated defects but often result in inefficiencies, extended maintenance times, and thermal damage. High-speed grinding (HSG) has emerged as an effective alternative, offering higher grinding speeds (60–80 km/h) and reduced "maintenance windows." Unlike conventional grinding, HSG operates through sliding-rolling composite motions, driven by frictional forces between grinding wheels (GWs) and the rail surface [9]. This unique mechanism enables both material removal and abrasive self-sharpening. However, the interplay between sliding and rolling motions has been insufficiently explored, limiting the potential of HSG for rail maintenance optimization. In this work, a home-made HSG test rig was employed to simulate on-site grinding conditions. Experiments were conducted under varying contact angles (30°, 45°, and 60°) and grinding loads (500 N, 700 N, and 900 N) [10, 11]. 

1. The ratio of Slide-roll. The results demonstrate that sliding-rolling composite motions play a crucial role in influencing grinding behavior. The sliding-rolling ratio (SRR), defined as the ratio of sliding speed to rolling speed, as shown in Fig.1, increased with both contact angle and grinding load, which intuitively reflected changes in the sliding-rolling composite motion of the grinding pairs. For instance, the SRR grew from 0.18 at a 30° contact angle to 0.81 at 60°. This shift from rolling-dominated motion to a balance between sliding and rolling significantly improved grinding outcomes. The study found that a 45° contact angle produced the highest grinding efficiency, while a 60° contact angle yielded the best surface quality, Surface roughness (Ra) decreased substantially as the contact angle increased, from 12.9 μm at 30° to 3.5 μm at 60°, as shown in Fig.2 to Fig.4.

2. Grinding-induced WEL.  During the grinding process, due to the thermo-mechanical coupling effects, including high contact stress, elevated temperatures, and rapid cooling, metallurgical transformations and plastic deformation occur on the rail surface. These changes lead to the formation of a brittle white etching layer (WEL), which is prone to fracture under cyclic stresses from wheel-rail contact. All of the results reveal that the average thickness of the WEL is less than 8 μm, which is thinner than the active grinding-induced WEL (~40 μm) [12, 13], as shown in Fig.5. This phenomenon is likely related to the unique characteristics of the HSG method, Compared to traditional active grinding, in HSG, a single abrasive particle engages in the grinding process for only a brief period during one revolution cycle, even at high contact angles. For the majority of the time, the abrasive particle is in the heat dissipation period after grinding. This ensures that the abrasive particle has sufficient time to dissipate heat before re-engaging in grinding, resulting in improved thermal conditions at the grinding interface.

3. Grinding debris. Grinding debris analysis provided additional insights into the material removal mechanisms, as shown in Fig.6 and Fig.7. Flow-like and knife-shaped debris, which signify effective grinding performance, were more prevalent at higher SRRs. In contrast, block and sliced debris were dominant at lower contact angles, reflecting inadequate grinding performance. The presence of spherical debris increased with grinding loads, indicating elevated grinding temperatures. These observations highlight the importance of optimizing grinding parameters to balance efficiency and thermal conditions.

4. Mechanism of sliding rolling compound motion. The study also revealed the dynamic interplay between sliding and rolling motions in the grinding process, as shown in Fig.8. Sliding facilitated material removal from the rail surface, while rolling enhanced debris discharge and abrasive self-sharpening. This dynamic balance is essential for achieving efficient grinding with minimal thermal damage. However, an excessive emphasis on either motion can lead to suboptimal results: rolling-dominated motion increases surface roughness, while sliding-dominated motion can result in reduced abrasive renewal and increased thermal damage.

5. Comprehensive evaluation. Comprehensive evaluations of grinding performance, including grinding efficiency, surface roughness, and WEL thickness, highlighted the advantages of optimizing sliding-rolling composite motions, as shown in Fig.9. The radar charts of grinding performance under various loads and contact angles showed that a 45° contact angle provided the best overall balance of efficiency and quality. However, the 60° contact angle consistently produced the smoothest surfaces, making it ideal for final grinding passes. These findings suggest that targeted adjustments to grinding parameters can address varying rail surface damage effectively.

This research offers practical implications for high-speed rail maintenance. For initial grinding passes, a 45° contact angle maximizes material removal efficiency, while a 60° angle ensures superior surface quality in finishing stages. The study underscores the importance of dynamically balancing sliding and rolling motions to enhance grinding performance, improve surface quality, and extend the service life of grinding wheels.

In conclusion, the study highlights the critical role of sliding-rolling composite motions in high-speed rail grinding. By optimizing the proportion of sliding and rolling actions, HSG can achieve superior grinding efficiency and surface quality while minimizing thermal damage. These findings provide a theoretical foundation for advancing HSG technology and practical guidelines for improving rail maintenance practices.

Fig. 1. Variation trend of SRR, COF, and rotation speed with grinding loads and contact angles.

Fig. 2. Grinding efficiency under different contact angles and grinding loads.

Fig. 3. The surface morphologies of rail specimens under different contact angles and grinding loads.

Fig. 4. Surface roughness and 3D morphologies of rail samples under different contact angles and grinding loads.

Fig. 5. Cross-sectional optical and SEM metallographic images of the rail specimens.

Fig. 6. The type and proportion of grinding debris under different contact angles and grinding loads.

Fig. 7. SEM images and EDS spectra for different types of grinding debris. 

Fig. 8. Schematic diagram of the effect of sliding-rolling composite motion on HSG.

This work has been reported on the Journal of Tribology International. 

References

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