What are the important causes of fishplate cracks?

After a crack occurs in the fishplate of railway equipment, it begins to expand slowly under a certain alternating load. This is the slow expansion zone of the crack. When the crack expands to a certain depth, the remaining cross-sectional area of the component is not enough to withstand the alternating load. When acting, the component will undergo instability and fracture to form a rapid fracture zone. These two regions generally have obvious characteristics.
From the failure research of fishplate, the factors that affect the crack expansion are mainly the load condition and material condition. The load condition includes many contents. It not only includes the size of the load itself, but also includes bad working conditions and A certain wheel speed, vehicle type, etc. bring additional impact loads and other forms of external forces to the rail joints. For example, the tightening bolt does not reach the specified tightening force, or the tightening force decreases due to increased wear of the fishplate, which will increase the additional impact force at the joint; the increase in wheel load, increase in vehicle speed, and uneven joints will also cause Joint stress increases. The condition of the material is very obvious. Good materials can ensure that cracks expand slowly.
Another important cause of fishplate cracks is the interaction between the rail and the fishplate. Therefore, how to reduce the adverse effects of this effect is a problem that remains to be studied. In addition, in recent years, while studying rail bolt hole cracks, some people have noticed the effect of fishplates on steel plates, and found that the current support form of fishplates with upper and lower slopes, that is, wedge-shaped supports, causes vertical tensile stress on the rail waist. , this stress intensifies the occurrence of cracks in the rail bolt holes. At the same time, railway equipment manufacturers believe that only by considering the fishplate and the rail as an inseparable system and studying the interaction between them can they ensure a good joint condition for the entire line and improve Line operation safety.