The Welded Joints Fatigue Life Analysis Of Excavator Boom Based On The Hot Spot Stress Method

Excavator is a major mechanical in the earthmoving operations, its working environment is harsh. As the main components of the excavator, boom is under big and various loads and easy to occur failure. Especially in recent years, with the development of mining machinery towards higher speed and heavier loads, excavator boom is in a significantly increased risk of failure. Statistics show that more than 80% of the component failure is caused by fatigue failure, therefore the fatigue study on the components that contributes to its safe and reliable operation.Excavator boom is a box structure which is welded by steel plates. Welding position not only has the biggest structure geometry shape changes, and is the welding heat affected zone, its stress is complex that leads to be the weakest position of the excavator boom structure. As a result, the fatigue assessment of welded joints of excavator boom has more practical meaning. The current application methods on fatigue evaluation mainly include: hot spot stress method, the nominal stress method, notch stress method and fracture mechanics method. In view of the weld structure of excavator boom, comparison of the above methods, this paper selects the hot stress method for fatigue assessment. The main work is done there:First of all, according to the excavator machine operation trajectory identified four kinds of typical working condition, based on the principles of selecting the most unfavorable conditions, select excavator boom working condition of the maximum stress position as the analysis and calculation of typical working condition in this paper. Excavator boom are also studied by use of analytic method in the mechanical properties of typical working conditions, build the mechanics model of the excavator boom.Secondly, according to the structure size of the excavator boom, Pro/E was utilized to establish the CAD model of the excavator boom, the element types and material properties are set in ANSYS, meshing to build the CAE model of the excavator boom. Determines the constraint and load on pin hole processing way, through the cloud after static load, select the maximum stress point on the welded joints of excavator boom in typical working conditions as a key position in the fatigue analysis.Finally, the S—N curve of structure is derived based on the hot spot stress, according to the actual situation of excavator boom select appropriate fatigue cumulative damage criterion, assessed the fatigue of the maximum stress point on the welded joints of excavator boom.Through the above work, the conclusion mainly include in this paper:1.The excavator boom loads of typical working conditions and the analysis results of finite element static show that the value of the maximum stress of excavator boom is 326.71 MPa, which below excavator boom material yield limit of 345 MPa. It shows that static strength of excavator boom under this condition is to meet the requirements.2. Hot spot stress concentration factor fitting using least square method and derive the hot spot stress S—N curve of structure by the nominal stress S—N curve of structure. Its proved to be feasible.3.This paper selects Miner Criterion as a method for calculating the life estimation. Based on the hot spot stress S—N curve of structure, estimate the fatigue life of the maximum stress point on the welded joints of excavator boom, prediction results are reasonable and acceptable.