| At present,China's high-speed railway has entered the stage of rapid development,and brake disc as one of the basic brake components of high-speed train,its operation safety is particularly important.With the increase of train speed and the requirement of braking capacity,transient friction heat energy and mechanical load cause significant temperature change of brake disc and thermal strain of friction surface.This coupled thermo-mechanical behavior will lead to macroscopical hot spots and fatigue cracks along the radial direction,which seriously reduces the service life of the brake disc.Cracks on brake discs are not single.Once cracks are formed,many micro-cracks with different lengths can be observed at the same time in most cases.Therefore,it is of great significance to study the relationship between surface cracks of brake disc and provide data support for predicting the life of brake disc.In this paper,according to the actual operation of high-speed train,a three-dimensional finite element model of forged steel brake disc is established.According to the actual size of the brake disc,a quarter cycle symmetry model is selected.The temperature field and stress field distribution of the brake disc are obtained by simulation calculation under three different working conditions with Abaqus finite element software.The analysis shows that the maximum stress and the maximum temperature occur before the end of braking,the maximum temperature occurs earlier than the maximum Mises stress,and the maximum temperature of emergency braking of the brake disc reaches 638.4? at the initial speed of 400 km/h.At the same time,due to the uneven distribution of temperature,the brake disc surface presents a high temperature zone.The radial stress of brake disc is less than the circumferential stress in braking process.Both kinds of stress are far greater than the axial stress,and the circumferential stress is dominant.Heat dissipation ribs can help brake discs increase heat transfer efficiency and reduce the residual stress of brake discs.Subsequently,the finite element model of semi-elliptical crack on the surface of brake disc is established,and the crack is inserted into the highest temperature position during braking process.The variation of stress intensity factor at crack tip with different inclination angles is obtained by numerical solution using the extended finite element method.It is found that the variation range of stress intensity factor at the deepest point of the crack tends to be flat with the increase of inclination angle.The mode II and III stress intensity factors have little contribution to the crack growth on semi-elliptical surface.The mode I stress intensity factor plays a major role in the crack growth.Finally,the calculation results of thermal elastic-plastic fatigue cracks and stress intensity factors under different shape ratios under emergency braking mode of high-speed train brake disc are studied in depth.The interaction rules of stress intensity factors between parallel cracks,radial dislocation and radial dislocation-free location are simulated for two groups of parallel cracks on the surface of brake disc.Data analysis shows that the crack depth-to-length ratio has a great influence on the variation of stress intensity factor at different locations of a single crack.When the depth-to-length ratio becomes larger,the gap between maximum and minimum stress intensity factor narrows,the trend of change tends to be gentle,and the direction of crack depth becomes a non-main propagation region.In the two parallel cracks,the long crack has obvious interference effect on the short crack,while the short crack has little influence on the long crack.When the radial or circumferential distance between two parallel cracks is very small,the shielding effect appears at the crack tip and decreases with the increase of the spacing.The stress intensity factors at the tip of two parallel cracks increase with the increase of their dislocation degree in a small range. |
PDF Full Text Request