Test Study On Fatigue Fracture For Forging And Casting Steels Of Grade E

The hook buffer is one of the most important connecting members of a train. In the buffer means, couplers are the critical components whose function is to connect the engine with the vehicle or the vehicle with the vehicle and transfer the traction and impact. So that make the carriages maintain a certain distance. When the train is on the way, the couplers will suffer alternating tension, compression and bending stress. Those alternating loadings would directly determine the working life of the couplers. Hence, it is significant to research on the fatigue fracture of the train couplers’steels for the trains’safe operation in practice.In this paper, the steels of train’s couplers (forging and casting steels of grade E) were mainly studied in the experiments. More details is as follows:In the first part, the traditional fatigue test is conducted. The up and down method is adopted to measure the two kinds of process steels’fatigue strength limit under the stress ratio-1and the number of stress cycle107. Although the difference of tensile strength are smaller, the inferior limit of fatigue strength for forging steel is twice as much as casting. Moreover, the modified Goodman fatigue limit diagram is plotted for the forging steel of grade E. The grouping method is adopted to measure the inferior limit of fatigue life and the S-N curve is fitted in the high stress level. In addition, combined the up and down and the grouping method test data, the overall S-N curves are fitted in the paper.In the second part, the fatigue crack growth rate test is performed. The "decreacing force" method is applied to measure the fatigue crack growth law and the threshold value in the near-threshold region. The constant force amplitude test is applied to measure fatigue crack growth laws for the two kinds of process steels in the stable region. As well as, the equations of the da/dN-△K curves are acquired under the different survival probabilities.In the third part, the fracture toughness test is conducted. The single-specimen method is used to measure the values of the critical J-integral for the two kinds of process steels. Then the values of the fracture toughness KIC are calculated.In the last part, the classic Priddle model is used to fit the test datas of the fatigue crack growth rate for the two kinds of process steels. The fitting results are perfect. Also, the da/dN-△K curves are acquired under the different survival probabilities. In addition, the Karl-Heinz and the WangHong models are also used to fit the test datas. The fitting results are either risk or too secure. Furthermore, the WangHong medol is extended and the new material constant C is defined. The extended model is used to fit the test datas and the fitting results are perfect.