A Simulation On Hardening Process Of A Steel Crankshaft And Prediction Of Fatigue Limit Load

Crankshaft is one of the most important parts of an engine.During the working process,it will be subjected to loads from different sources which can cause the fatigue damage of the crankshaft fillet,oil hole and other parts due to the stress concentration.At the same time,the requirement of the fatigue strength of the crankshaft is becoming higher and higher because of the lift of the engine's burst pressure and lightweight design.The surface induction hardening process can produce the residual stress of the crankshaft connecting rod and the fillet,and then improve its fatigue life.Because of the powerful function of analysis and visualization capability,the computer provides the possibility of simulating the strengthening process of the crankshaft surface.How to avoid a large number of experiments and use the theoretical method to obtain the fatigue limit load of the crankshaft is of great significance for practical engineering.Therefore,selecting the right method to predict accurately the fatigue strength of crankshaft in the design stage is of importance for the design of crankshaft structure and fatigue resistance.This thesis takes the engine crankshaft as the research object,and uses the finite element method to analyze the stress of the crankshaft under the bending moment load.The nominal stress method is used to select the fracture surface of the crankshaft main journal,and the fatigue ultimate load of the crankshaft is predicted.In order to determine the critical plane of the crankshaft and the type of fatigue damage,the coordinate transformation method is used to analyze the stress state in the area of the stress concentration area.By using the critical plane method and the shear failure model,the fatigue limit load of the crankshaft is obtained without quenching process.On this basis,the 2-D axisymmetric model of crankshaft is established by ANSYS software.The thermosetting coupling function is used to simulate the intermediate frequency induction quenching process of connecting rod journal,and the distribution of temperature field is obtained.The extended analytical model of dynamics and superposition principle are used to determine the depth of hardened layer in the austenitizing process and the hardened layer at the connecting rod from the parent body,which has different material properties.The distribution data of temperature field are imported into the force field as load,and the distribution of residual stress field is obtained by analyzing the crankshaft.Then,the nominal fatigue method and the fatigue damage model based on critical plane are used to calculate the fatigue ultimate load of crankshaft quenched.Compared with the fatigue test data,it is shown that the fatigue limit load of crankshaft can be predicted accurately by using the quenching simulation and the critical plane method.After the crankshaft isquenched,the fatigue limit load can be greatly improved,which provides a basis for the design stage of the crankshaft.