Research On Growth Of Fatigue Crack Of Rail Steel Under Moment Of Flexure Condition

With the developing of national economy and the beginning of the Eleventh Five-year Plan, railway transportation, especially high speed railway construction, is more and more important. Compared with developed countries, our country's technology of high-speed railway is not perfect. Some unknown problems have been discovered in the quasi high speed railway, especially rolling contact fatigue. For example, Oblique Crack of PD3 and U71Mn rail have been discovered in Guangzhou-Shenzhen railway. So it is very important for the development of our country's high-speed railway to analysis and research the crack's initiation and growth.The new test rig has been successfully developed by modifying the clamps and the control programs from the fretting apparatus with high precision. Through changing of experimental parameters, such as load amplitude, loading rate which effect on fatigue properties, this paper researched fatigue properties of steel rail. Experimental results have been analyzed in detail by means of optical microscopy (OM), hardness tester, and scanning electron microscopy (SEM). Main conclusions are drawn as follows:1,A new experimental apparatus has been developed to really simulate installation form of railway. The experimental realized the normal load, laying an experimental foundation to researching influence of moment of flexure. Tests can be done on mode of imposed load. The loading rate and loading amplitude can be controlled by the system computer. Results showed a better comparable characteristics and repeatability.2,Morphology of crack under static load was great different than which under dynamic load. Crack propagation path under static load appeared sudden change. At the same time, the growth of crack under dynamic load was more stable than that under static load. 3,Loading rate has different influence on the different materials. PD3 rail is more sensitive to loading rate than U71Mn rail. Under same loading amplitude and different loading rate, growth of crack of PD3 rail was different form U71Mn rail.4,PD3 rail's fatigue properties was different from U71Mn rail's. Under low cycle, crack has been discovered in PD3 rail, but there was no crack discovered in U71Mn rail. The results show that U71Mn rail have better fatigue properties than PD3 rail.