What are the situations where the rail surface is damaged?

It is generally believed that the shear stress under the rail surface caused by the contact stress is the main reason for the rail damage caused by the vertical force. Due to the interaction of the wheel and rail, contact stresses repeatedly appear on the top surface of the rail, causing plastic deformation, fatigue wear and fatigue cracks on the rail surface.

1.    Plastic deformation and wear of rail head

The plastic deformation of the rail is directly proportional to the contact stress and inversely proportional to the hardness of the rail. When the contact stress is close to the shear yield limit of the rail, the contact surface begins to plastically deform. When the contact stress reaches 4 times the shear yield limit, the contact surface exhibits continuous accumulation of plastic deformation, which causes the rail head to be widened or rolled, and compression occurs. At the same time, the metal on the top surface of the rail is hardened and the hardness is increased. Fatigue cracks appear on the surface, resulting in flaky peeling. This is also the surface fatigue wear caused by contact stress.

2.    The rail surface is peeled off

When the contact shear stress is caused by the contact stress, the plastic flow deformation layer is deeper, and the surface fatigue cracks develop obliquely downward along the rheological direction. When the fatigue crack growth rate is greater than the wear, the small circle on the inner side of the rail top with greater contact stress A fish-scale peeling crack appears at the arc, and the depth of the peeling crack corresponds to the plastic deformation. Generally, it can reach more than 2mm at the outer rail of the small radius curve. The adhesion and creep of the curved outer rail wheel and rail promotes the development of cracks. The front and rear fish scale cracks penetrate through and break off. Due to the uneven track, the impact force of the wheel and rail is increased, and the crack development is accelerated. If there is non-metal in the steel Inclusions accelerate the initiation and development of cracks.

3.    Nuclear damage to the rail

Nuclear damage is caused by internal fatigue cracks within the range of 5--12mm below the rail head tread. This range is the area where the contact shear stress is the largest. If there are oxide inclusions in this range, strip fatigue will be formed. crack. After the transverse fatigue crack develops to a larger size, the transverse crack may develop under the dynamic load of the wheel.

4.    Corrugation of rails

Corrugation refers to the periodic uneven undulating deformation on the rail tread. There are many reasons for the formation of corrugation. It is generally believed that when the wheel is driving on a curve, it has the effect of "frictional self-excited vibration", which causes repeated adhesion and sliding of one wheel, and plastic deformation and abrasion of the surface of the rail during the sliding process. Wave troughs, crests appear in the adhesion process. The contact stress at the wave trough increases sharply and the plastic fluidity deformation of the metal increases, which intensifies the development of corrugation.