| With the development of railway transportation in our country, train axle load becomes more and more big, and the speed of the train is becoming more faster. During the process of production or use of rail, some minor defects come into being. In the process of wheel rolling-slide, under the action of wheel/rail contact force repeatedly, crack is generated easily on wheel/rail contact area, crack propagation and eventually develop into falling off, the more serious one may grow into fracture. Based on the wheel/rail rolling sliding contact theory, the thermal contact theory and the fracture mechanics, the rail head surface crack propagation characteristics under the condition of wheel rolling-slide were researched as follows:First, a purely mechanical model for wheel-rail contact in pure sliding state is established, and use the large finite element software ABAQUS to analysis the stress field in the cases of preset, from the distribution of whole rail stress field, maximum stress area distribute on head left side, stress distribution rail head oval shape.Second, introducing surface crack into rail head of mechanical model for wheel-rail contact in pure sliding state, analyzed and calculated the crack tip stress intensity factor respectively under the different axle load and the coefficient of friction between wheel and rail, the different angle of crack surface and the top of the rail and different crack depth, the results show that the crack tip stress intensity factor increases with the increase of axle load and wheel/rail friction coefficient. In the four parameters, friction coefficient between wheel and rail is the most sensitive factor to the stress intensity factor, followed by the crack angle.A thermal-mechanical coupling model for wheel-rail contact in pure sliding state is established, then, rail surface crack is introduced in the model, and calculating the crack tip stress intensity factor under various factors change. The results show that the maximum equivalent stress under thermal-mechanical coupling loads is bigger than the value of the purely mechanical loads by 3%. Under the action of thermal-mechanical coupling, the crack tip stress intensity factor is generally lower than the value of the purely mechanical loads, because of the temperature load have played an important role of restraining crack propagation.By introducing wheel angular velocity, a thermal-mechanical coupling model for wheel-rail contact in pure rolling state is established, and calculated the train rail stress field and temperature field when running at a speed of 100 km/h, the results show that the position of the rail maximum equivalent stress is behind the rear wheel, because shear stress backward function under rolling contact, the area behind contact spot bear the compression, in front of the contact spot bear the tensile, shear stress of extruding and contact pressure of superposition effect makes the stress behind the contact spot is very large. Contact spot temperature is 377 ℃, also slightly higher than the thermal-mechanical coupling effect in sliding state’s highest temperature.Finally, introducing surface crack into rail head of mechanical model for wheel-rail contact in pure rolling state, and calculate the crack tip stress intensity factor under different axle load,coefficient of friction between wheel and rail, angle of the crack surface and the top of the rail and the crack depth, in the case of larger plastic zone appears, calculated three kinds of crack tip displacement CTOD, CTSD and CTD respectively, the results show that the shear stress intensity factor KⅡ affected by the changes of axle load is serious, but the crack expansion patterns under different axle load have little change; And with the change of friction coefficient, the crack expansion patterns changes, too; Expansion patterns has little change while crack depth changes; As the crack surface and the rail top angle change, shear and tearing expansion mode dominated, while open type extension mode weaker. |
PDF Full Text Request