Study On Root Cause Of Metro Rail Corrugation And Its Influence On Behavior Of Vehicle-Track System

Rail corrugation is one of the puzzle in wheel/rail rolling contact. Rail corrugation phenomena become the universal problem with the rapid development of the urban subway transits in China. Noise and vibration issues caused by wheel-rail rolling contact become serious due to rail corrugation phenomena. It not only results in the discomfort for passengers, the use life reduction of vehicle and track structural parts, but also endangers the transportation security. The cause of rail corrugation appears great diversity, and there has not been an identical conclusion so far. Therefore, further study on the cause and influence of rail corrugations is useful for design, construction and maintains of track. It also can be very important to provide guarantee for the safety and reliability of train operation.Based on the field investigation and numerical simulation, the thesis mainly carried out the following aspects of research work.(1) The studies on rail corrugation in the world are summarized and reviewed. The necessary for the study on the cause and influence of metro rail corrugation are pointed out.(2) The thesis gives a detailed investigation into the rail corrugation of China metro. According to the characteristic of the corrugation, track structures and vehicle operation conditions, the corrugation in the metro are classified as five categories, (a) short-pitch corrugation for elastic fasteners, which happens on the tracks with resilient fasteners (Vertical static stiffness is less than 20 kN/mm). It has the wavelengths of 30-63 mm and the passing frequencies of 200-840 Hz at train operation speeds of 40-90 km/h. (b) P2 resonance corrugation, which occurs on the small radius curved tracks with common (traditional) fasteners (static vertical stiffness is larger than 40 kN/mm). This corrugation has the wavelengths of 100-250 mm and the passing frequencies of 50-140 Hz at the speeds from 35 to 70, which is similar with the P2 resonance frequencies of wheelset-track. (c) Corrugations for short sleeper with resilient rubber (booted sleeper), which occurs on small radius curved tracks with booted sleeper. It has the wavelengths of 50-160 mm and the passing frequencies of 130-280 Hz at the speeds of 50-90km/h, which is related to the characteristics of the track, (d) Ladder sleeper corrugation, which only happens on the curved tracks with ladder sleeper. It t has the wavelengths of 80-200 mm and the passing frequencies of 80-200 Hz at the speeds of 35-80 km/h. (e) Short-pitch corrugation related to sleeper space, which happen on the tracks with sleeper space of 0.625 m and common fasteners.(3) A 3D dvnamic model of a subwav train coupled with a slab track in time domain is developed. The field experiments are conducted to verify the train-track model developed in this study. The model consists of three subsystems:the train system, the track system, and the wheels and rails in rolling contact. The tested train consists of four power vehicles and two trailing vehicles. Each vehicle modelling considers one car body, two bogie frames, eight axle boxes and four wheelsets. And the interaction between adjacent vehicles occurs via the inter-vehicle connection. The slab track, consisting of a pair of rails, fastenings, track slabs, and the roadbed, is modelled. The model consists of two Timoshenko beams for the rails, a 3D solid finite element model for the slabs, periodic discrete viscoelastic elements for the rail fastenings that connect the rails and the slabs, uniformly viscoelastic elements modeling the subgrade beneath the slabs, and 3D spring elements simulating the connectors between neighboring slabs. The vehicles and the track is coupled through the wheels and rails in rolling contact. The spatial geometric problem of wheel-rail contact is solved in transient condition. The numerical results basically agree with the results of field test.(4) A linear model of corrugation in frequency domain is used to calculate the rail wear formation concerned with the corrugation and track characteristics. In the numerical model, a wheelset-track structural dynamics model is interacted with a rail wear model. In the numerical simulation, the initial irregularities of track are used into the wheelset-track structural dynamics consisting of track, wheelset and wheel-rail contact. In the model, the receptances or mobilities for the tracks are experimentally obtained in field test. According to the field investigation, the effect of wheelset flexibility is neglected in the model. The Hertz and Vermeulen-Johnson theories are adopted to solve the wheel-rail normal and tangential contact problem, separately. In the wear model, a frictional power hypothesis is used to determine the wear of rail surface.(5) The thesis uses the linear corrugation model described above to analyze and explain the formation cause of metro corrugations in different track structures. The influence of vehicle speed on the rail corrugation is also investigated. It is found that the formation and development of rail corrugation easily occur in the frequency ranges with the low value of track receptance.(6) A series of field experiments are carried to investigate the influence of short-pitch rail corrugation on the vibration and noise of the vehicle and the track. The results measured show that the effect of the corrugation on the vibration and noise is significant. The short-pitch rail corrugation is the main cause of abnormal vibration and noise generation when a train is passing by. Rail grinding can eliminate the abnormal vibration and noise effectively. Besides, The influence of out-of-roundness of wheel (or wheel corrugation) on the accelerations of axles and bogies is significant. But it is found that the interior and exterior noise of metro train is not sensitive to the investigated out-of-roundness of wheel. Attenuation of vibration caused by the wheel out-of-roundness is not strongly dependent on the primary suspension system.(7) The three-dimensional finite element models for the primary coil spring and the rail fastening clip are developed to investigate the effect of short pitch rail corrugation on the dynamic behaviors of the primary coil spring and the rail fastening clip. Through the numerical investigation, the fracture mechanism of the spring and the clip are understood and measures of controlling the failures are proposed. The results show that (a) the influence of the corrugation on the fatigue lives of the coil spring and the clip is significant. The fatigue lives of the coil spring and the clip reduce rapidly as the corrugation depth increases or the corrugation wavelength decreases; (b) When the vehicle passes over the corrugated track rails, the natural frequencies of the spring and clip are close to the passing frequencies of the corrugation, and the system resonance occurs, which is also one of the causes of their failures. In order to control their failures, the amplitude of corrugation with wavelength of 30-40 mm should be below 0.08 mm; (c) To reduce the failure of the fastener clips, it is necessary to increase the radius of the clip shoulder end arch to 8 mm and keep the smooth of the shoulder end. In track operation and maintenance, the distance between the inner arc of the clip rear arch and the shoulder end should be controlled within 8-10 mm.(8) To control the metro rail corrugations, the existing acceptance criteria for rail grinding should considers the effect of the three important factors, corrugation depth, its wavelength and train operation speed simultaneously. Two assessment quantities for running safety and wheel-rail interaction, which is related to fatigue damage of the track components, are considered in determining the corrugation amplitude limit. For the corrugation with the wavelengths of 30-80,80-120 and 120-200 mm, their corresponding amplitudes should be controlled below 0.03,0.1 and 0.25 mm, at train speeds below 120 km/h. Based on assessment of wheel-rail rolling contact fatigue, acceptance levels for rail roughness with the wavelengths of 30-65,65-125 and 125-250 mm should be below 5.4,24.8,33.8 dB re 1?m, separately when the train speed is less than 80 km/h.