| 280 combined pistons had well been used on diesel engines of DongFeng series locomotives for a long time. While after 2001, with the speeding up of trains in our country, several fatal accidents had happened during mid-term maintenance period.Several relative sections cooperated to probe the causation of the failure. Plenty of work were done on the macro and micro fracture area, composition analysis, microstructure and mechanical properties of the bolt hole transitional fillet area, the result show that the failure is caused by metal fatigue, considering the working condition of 280 combined pistons.The structure of the piston is improved to meet the requirement. Thermal and stress field analysis via FEM are conducted according to appraise the effect of the improving action. The emphasis of this paper is to simulate the thermal field, probe the exact temperature near the fillet area via FEM, and get the temperature load for the following stress filed calculation. The structural mould is set up by Pro/E and then exported into ANSYS for the following calculation. After tens of times of calculation and adjustment the value of FEM got thermal filed get in accordance with the several measuring got temperature, so we got the thermal boundary condition. The result show that the calculating got temperature is almost the same with the measuring got temperature on the same area, showing the reliability of the calculation. There is only a 3℃~7℃subtraction of temperature near the fillet area, and the overall temperature variation is also not clear.The compare of wear behavior test shows that the wear behavior is almost the same despite the difference of supplying place.
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