Adhesion and Damage Behaviour of Wheel–Rail Rolling–Sliding Contact Suffering Intermittent Airflow with Different Humidities and Ambient Temperatures

The adhesion and damage behaviour of wheel–rail systems play an important role in the safety of railway operations. To verify the low adhesion behaviour of wheel and rail contact during the train entering tunnels in alpine regions caused by intermittent humid and warm airflow, tribology testing using a rolling–sliding contact in the laboratory was conducted to investigate the effect of humid and warm airflow with various ambient temperatures (− 55 to 60 °C) and airflow with different humidities (relative humidity from 5 to 99%) on the instantaneous low adhesion and damage failure between the wheel–rail interface. Results indicate that the instantaneous low adhesion phenomenon and multifarious damage are affected by the humidity of the airflow and the ambient temperature. In the temperature range of − 55 to − 20 °C, the wheel–rail interface will be in a low adhesion state once it encounters a humid and warm airflow attack. As a result, the adhesion coefficient curve exhibits a ‘comb-shaped’ feature. In this temperature range, the wear surface is rougher under the action of high moisture flow, and the main damage mechanism is fatigue wear. In particular, the moisture in the airflow will liquefy into water or even condense directly into frost and ice film on the wheel when the humid and warm airflow encounters the cold wheel surface. Consequently, the adhesion coefficient exhibits a ‘comb-shaped’ feature. In the meantime, the tribological oxidation reaction is more active at humid airflow conditions of 40–60 °C. The high humidity environment is conducive to the formation of water paste during friction, that is, a mixture of oxidized debris and water molecules that acts as friction-reducing layers, which also reduces the adhesion coefficient. These results will help deeply understand that, the wheel–rail adhesion coefficient drops sharply in an instant once the wheel–rail interface encounters the humid and warm airflow in the tunnel. Thus, railway operations department have to be very cognizant of the low adhesion problem, and take effective measures to improve the adhesion of wheel-rail interface to avoid the occurrence this kind of problem.