Intelligent Preload Monitoring Technology and Track Condition Early Warning Scheme for Fastening Systems
What are the main causes and hazards of preload attenuation in fastener systems?
The main causes of preload attenuation in fastener systems include bolt loosening, elastic bar fatigue and environmental factors. Bolt loosening is mostly caused by high-frequency vibration generated by train operation, which will reduce the friction between bolt threads and cause gradual loss of preload. Elastic bars will produce fatigue deformation under long-term alternating loads, the elastic modulus decreases, and the original preload cannot be maintained, this attenuation is irreversible. Environmental factors such as high temperature, low temperature and humidity changes will lead to the thermal expansion and contraction of fastener components, destroy the stress balance of the fastener system, and accelerate preload attenuation. Preload attenuation will lead to the loosening of the connection between the rail and the sleeper, the increase of longitudinal and lateral displacement of the rail, and the exceeding of geometric parameters such as gauge and level of the line. In severe cases, it will cause faults such as rail creep and fastener fracture, and even lead to train derailment, resulting in major safety accidents and economic losses.
What is the core sensing technology for intelligent preload monitoring of fastener systems?
The core sensing technologies for intelligent preload monitoring of fastener systems are fiber Bragg grating sensing technology and piezoelectric ceramic sensing technology. Fiber Bragg grating sensors have the characteristics of small size, anti-electromagnetic interference and corrosion resistance, which can be embedded in elastic bars or bolts. The preload is calculated by detecting the change of grating wavelength, and the measurement accuracy can reach ±1%. The response time of the sensor is ≤10ms, which can capture the dynamic change of preload in real time, and is suitable for use in the railway environment with strong electromagnetic interference. Piezoelectric ceramic sensors are based on the piezoelectric effect. When preload acts on the sensor, it will generate a charge signal proportional to the pressure. The preload data is obtained by detecting the intensity of the charge signal, and the measurement range is 0-100kN, which meets the monitoring needs of different fastener systems. Both sensors can realize passive design without external power supply, and send data to the background system through wireless transmission modules, reducing the difficulty of on-site installation and maintenance.
What are the composition and working principle of the intelligent preload monitoring system for fastener systems?
The intelligent preload monitoring system for fastener systems consists of four parts: sensing unit, data acquisition unit, wireless transmission unit and background analysis unit. The sensing unit is composed of fiber Bragg grating sensors or piezoelectric ceramic sensors, installed between the elastic bar and the gauge block or at the bolt head to directly sense the change of preload. The data acquisition unit amplifies, filters and converts the weak signal output by the sensor into a digital signal through a signal conditioning circuit, the sampling frequency is controlled at 100Hz to ensure the continuity and accuracy of the data. The wireless transmission unit adopts LoRa or NB-IoT technology to send the collected data to the base station, with a transmission distance of up to 5km, meeting the needs of long-distance monitoring of railway lines. The background analysis unit conducts real-time analysis of preload data based on big data algorithms, establishes a preload attenuation model. When the preload is lower than the set threshold, the system will automatically send an early warning signal to notify maintenance personnel to deal with it in time.
What are the differences in threshold setting for preload monitoring of fastener systems in different line types?
The differences in threshold setting for preload monitoring of fastener systems in different line types are mainly determined by the axle load, operation speed and service environment of the line. High-speed railways have fast train operation speed and high vibration frequency, and have high requirements for preload stability. The preload early warning threshold is set to 80% of the rated preload, that is, when the preload attenuates to 80% of the rated value, the system sends an early warning, and the rated preload is generally 35-40kN. Heavy-haul railways have large train axle load and large load impact, and the preload attenuation speed is fast. The early warning threshold is set to 75% of the rated preload, and the rated preload is 45-50kN to ensure that the rail will not loosen under heavy-haul loads. Ordinary-speed railways have low operation speed and axle load, and the preload requirement is relatively low. The early warning threshold is set to 70% of the rated preload, and the rated preload is 25-30kN. Urban rail transit lines have frequent train starts and stops and many vibration impacts, the early warning threshold is set to 85% of the rated preload, and the rated preload is 30-35kN. In addition, the preload threshold of alpine lines should be appropriately increased, because low temperature will lead to the decrease of elastic bar elasticity and accelerate preload attenuation.
What is the impact of intelligent preload monitoring technology for fastener systems on line maintenance mode?
The intelligent preload monitoring technology for fastener systems promotes the transformation of line maintenance mode from periodic maintenance to preventive maintenance. The traditional periodic maintenance mode checks and maintains the fastener system according to a fixed cycle, which has the problems of insufficient maintenance or excessive maintenance, with low maintenance efficiency and high cost. The preventive maintenance mode is based on the real-time data of the monitoring system, and only performs targeted maintenance on the fasteners with excessive preload attenuation, avoiding undifferentiated comprehensive inspection, and greatly reducing the maintenance labor and material costs. Monitoring technology can also realize the digital management of maintenance work. The background system can record the preload change trend of each fastener, provide data support for the formulation of maintenance plans, and make maintenance work more scientific and targeted. In addition, preventive maintenance can effectively reduce line faults caused by preload attenuation, reduce line outage time, improve line operation efficiency and safety, and realize the optimal control of line life-cycle costs.