| The piston bears periodic heat load and mechanical load when the engine is working.Now days, the engine develop toward highly fortified, supercharged, high power per liter,which will inevitably t result in the increasement of the load in piston because of the increaseof engine speed and power. As the key part of engine, the solution of this problem isimportant for the development of overall engine technology , which can directly affect thereliability and durability. In other words, the heat load and mechanical load is an organicwhole It is not proper for us to study only one side alone to check whether the piston couldmeet the requirement or not.After the junk ring measurement for the piston that we discussed in this paper, themetallographic structure has changed in the fire face because of the casting defects, whereappears an annular marks. In order to analysis this Engineering problem clearly, the papercalculated the stress and strain fields during the mechanical load，thermal load, and thethermal mechanical coupling conditions respectively. Through the comparison with theoriginal piston, then the paper discussed the influence on the overall piston performance afterthe change of metallographic structure. In the end, strength check was made to confirm itsstructure strength to meet the design requirements of structure strength.The specific process is as follows:（1）A half part model of the piston has been built in this paper by using PRO/E;（2）The paper built finite element model after some simplifications with the specializedprocessing software Hypermesh;（3）Using empirical formula calculate heat transfer coefficient and the corresponding temperature parameter of all parts of the piston;（4）exported the mesh to ANSYS, then analysis the stress and strain fields during themechanical load，thermal load, and the thermal mechanical coupling conditions respectively;（5）put forward a research method for the change of metallographic structure, which Iassumed that all the region are damaged，then a ring groove with dimensions of 0.5 mm highand 0.8 mm deep was cut out instead;（6）The paper calculated the stress and strain fields of the grooved piston, and thancompared with the original model.The analysis results show that the groove plays a certain role of heat insulation,which takes more heat flow to the second groove and less temperature left in the fist groove tothe contrary.Besides, the temperature in the second and third grooves are increased slightly.The analysis results also indicated that the stress fields between grooved and the originalpiston model appear only a little difference. Its structure strength meets the designrequirements because of the worst assumation of the damage in changed regions. |
