Research On Stress Intensity Factor Of Surface Crack Of High-speed Train Hollow Axle

ABSTRACT:The axle is a key bearing part of a locomotive and the fatigue damage directly endanger the transportation security. Cut shaft fracture is one of the major causes of the railway vehicle overthrown accident, which has very strong concealment and suddenness. The train works in a complex system and its running condition may become more sever with the speed increasing. Under this environment some damage may occur on the axle surface. So some cracks can initiate from the damage and grow to the critical size, which will bring great hide safe trouble. Therefore, it is necessary to research the crack propagation rules to consider the damage limit of axles deeply and then we can give better advices for the examine and repair period.This paper is supported by the national basic research and develop project, the stress intensity factor of the surface crack of hollow axles of the high speed train is studied which is very important for the axles examine and repair management. The mainly work are as follows:1. In order to use the finite element method to calculate the stress intensity factor along the crack front, the derivation of virtual extended algorithm was done. On the basis of 2D J integral energy definition, using energy variational principle and green theorem the three-dimensional J integral formula was deduced. Through the crack virtual expansion technical and the displacement and stress from finite element analysis J integral was calculated and J integral expression was presented, without considering volume force and the crack surface force, and the relevant technology of integral J using the finite element method.2. According to the actual situation of axle surface accidental injury the influence of crack angles on the stress intensity factor was studied. Consider the lateral and longitudinal crack deflection in facts, the surface defects were analyzed of hollow axles. Through determining crack load conditions and simplifying crack entity model the intensity factors under different relative crack depths and different angles were calculated. The result shows that regardless of the type of stress intensity factor which will increase along with the increase of the depth of crack propagation. While the value of type I stress intensity factor is bigger than the ones of typeâ…¡andâ…¢. The maximum value of type I stress intensity factor appears when there is no deflection, that is to say the crack area is perpendiculars to the principal stress direction.3. The axle sevice loading was analyzed and the calculation method of bending stress on the axle surface was given. The stress variation on the axle surface under rotatory bending loading was discussed. The superposition method was proposed to get the stress intensity factor under different rotation angles.4. The stress intensity factor model under the torsional loads was established and three kinds of stress intensity factors were discovered. From the results we can find that the crack effects the symmetry of the axle, so there is not only torsional shear stress but also normal and transverse shear stress, which induced deformation at the crack front.5. Stress intensity factor of type I under bending-torsional loading was studied. For a flat crack which the aspect ratio is very small, due to the existence of torsional loads, the values of the stress intensity factors are bigger than the ones under pure bending except the deepest point of the crack. Otherwise, for a crack with bigger aspect ratio the influence of torsion loading is very small. 6. The stress intensity factor at the interference fit area was studied compared with the one at non- interference fit area. The result shows that the axial stress change tends to be gentle at the side with tensile at the cross section because of the interference fit. When the bending moment is vertical to the crack axis the values of stress intensity factor outside the fit are bigger than the ones without fit. Due to the interference fit the stress intensity factors at the surface points increase markedly, which makes the crack propagation tend to flatting.