Analysis Of Fracture In The Neck Of Intate Valve And Optimization Design

Inlet valve, as actuators of valve-train diesel engine, plays a role in air inflowing and sealing, so the performance of the inlet valve directly affects the performance of the engine. Inlet valve not only bears erosion corrosion of the high temperature gas, but also stands high strength, wear and high frequency alternating voltage. In the circumstance of bad weather,all the factors of improper material selection, defective organization performance and unreasonable structure design can lead to valve failure, in which neck fracture failure is a common failure mode.In this paper, the fracture in the neck of inlet valve was analyzed and the design of inlet valve's structure was optimized. Firstly, I analyzed inlet valve's material and processing technology of the valve by means of JSM-6490 LA SEM, Olympus GX51 stereomicroscope and TH320 Rockwell apparatus, which are used to observe and analyze macro profile and micro organization, determine chemical components and test hardness.The results show that there are too much C, O and Si in the inlet valve.These elements in the matrix form bulk metallic inclusion, resulting in the micro holes, which destroyed the continuity of the matrix, and to a certainextent, increased the brittle of material, resulting in fatigue crack appearing.It can be clearly observed that there are some continuous large holes near the fracture. What is more, the hardness near the fracture is uneven which is resulted from improper heat treatment. The inhomogeneity of microstructure will affect the uniformity of hardness distribution, reducing the impact toughness and fatigue strength of the material. High cycle fatigue fracture of the valve occurs in the working environment of high strength, high temperature and strong corrosion.Secondly, the neck of the valve is not only the transition zone of the stem and the disc, but also the stress concentrated area. The irrational structure will lead serious stress concentration, promoting the generation of fatigue source, which is one of the main reasons for the fatigue fracture.Start with optimizing the structure of the intake valve's neck, by using the finite element software-Abaqus to analyze the valve thermal- stress coupling and to optimize the structure of the valve. We obtained the stress distribution, and found the position of stress concentration. Then, we changed the cone Angle beta and transition arc radius R changes of the valve by solid works, and then imported them into the Abaqus to perform an analysis. In order to find the minimum of maximum stress and make the stress distribute uniformly, we studied the influence of beta and R to maximum stress and stress distribution.With this standard of the indicators for valve axial maximum stress,we change R and beta and analyze its stress. The results show that when?=21° R=21mm, the maximum equivalent stress is minimum. When the transition arc radius is 21 mm and transition taper Angle is 21°, the structure is the best. With this standard of maximum stress of valve plate,we increase R and Angle beta to analyze the maximum stress. The results show that when ?=21°, R=19 mm, the structure is the best.Integrating the results of analyzing the indicators for valve axial maximum stress and the maximum stress of valve plate, it can be found when ?=21°, R=21mm, its maximum axial stress is less than 21°, R=19mm.While in ?=21°, R=21mm, the maximum stress of valve plate is as much as the condition when ?=21°, R=19mm. So we choose ?=21°,R=21mm for the best structure.In this paper, the optimization results can be directly used in the processing and design of valve. And it could provide reference for optimizing the structure of the valve and improving the quality of the inlet valve.