Research On The Fatigue Deterioration Mechanism Of Type E Clip Fastener System In Subway

Fastener system provides elasticity for track structure and keeps track geometry, which is vitally importance to guarantee the track stability and safety. In recent years, due to the continuous improvement of subway traffic and reduce of running interval, the problem of fatigue deterioration of fastener system is increasingly serious, which threatens running safety and restricts the improvement of transportation efficiency. Therefore, to solve the problem of fastener failure effectively, this paper systematically studies the fatigue deterioration mechanism of fastener system based on the analysis of static, dynamic force and spectrum, essentially reveals the fracture mechanism of elastic bar, predicts the fatigue life of elastic bar, puts forward optimized design schemes based on the research. The main work and conclusions are as follows:1. Subway fastener system detailed finite element model is established according to real size. Contact relation and boundary conditions are separately dealed with nonlinear contact theory and nonlinear Cartesian springs. The forth strength theory is chosen to be the elastic bar strength evaluation index.2. To reveal the fracture mechanism of elastic bar from stress and strain views, static force distribution characteristics of elastic bar in various installation states are researched systematically. The results show that the elastic bar fracture is owing to the too small distance between the inside of rear arch and iron tie plate bearing, the stress inside of rear arch and close to mid leg is concentrated and increased rapidly, under the cyclic loading, extruding and rubbing, the elastic bar is injured at last. The lifting amplitude and insertion depth of mid leg are the major causes leading to elastic bar fracture.3. Elastic bar-iron tie plate finite element dynamic model is established to analyse the vibration characteristics of elastic bar in natural and service conditions with time-frequency method, to discuss the fracture mechanism. Elastic bar mechanical indexes and corrugation are tested by an experiment to discuss the internal relations among elastic bar natural frequencies, vibration modes and corrugation passing frequency. Analysis in frequency domain shows that, the essential reason of elastic bar fracture is that it is aroused resonance stimulated by certain external frequencies, and the frequencies are the ones corresponding to elastic bar acceleration and displacement admittance peak. Resonance increases the vibration amplitude of elastic bar, and increases the tensile-compressive stress and torque in rear arch (combined with vibration modes), so leading to fatigue fracture. Spectrum analysis of test results show that, the first and second resonance frequencies of elastic bar in natural and service conditions (808Hz～812Hz、869Hz/410Hz～420Hz、530Hz) agree with the corrugation passing frequency in test section. According to the studies, rail corrugation in subway lines is the main external cause leading to elastic bar fracture.4. The ABAQUS/FE-SAFE module is edited to study the fatigue property of elastic bar under vehicle cycling load and predict its fatigue life, then, the design of elastic bar is optimized. The research shows that, when d (distance between rear arch and iron tie plate) is 1.5mm or d is 3mm, h is equal to 14mm, the fatigue lives of elastic bar are not qualified, lower than 5 million times, when d is 1.5mm, h is equal to 14mm, the theoretical normal working time of fastener system is only eight months. Therefore, the error matching and unreasonable installation of lifting amplitude and insertion depth of mid leg are the major causes leading to elastic bar fracture.5. An optimum design of elastic bar is carried out based on the consequence of the research. The lifting amplitude h should be controlled between 10mm and 12mm, distance d should be controlled between 3mm and 9mm; refer to the wavelength of rail corrugation, changing the weight of iron tie plate or other parts of fastener, changing the stiffness kt value of rubber tie-plate, or changing the running speed, are effective ways to avoid the resonance of elastic bar.6. Vehicle-track-tunnel space coupling dynamic analysis model is established to discuss the dynamic effect mechanism of track structure and running safety on fastener deterioration. The research shows that, failure of fastener system increases dynamic response of track structure, especially increases the reaction of support of both sides of adjacent 4 fasteners, which causes large-area fastener disease in the condition of big density operation.