| The working device of the excavator bears the complexed loads during the operation.Therefore,its fatigue strength affects the service life and performance of the whole excavator,directly.However,the main body of the working device is a welded structure,so crack or break is easy to occurat the structural weld position,which becomes the weak point of the whole machine.So,fatigue life assessment of hydraulic excavator working devices is necessary,and it can provide a theoretical basis for the anti-fatigue design of hydraulic excavator products,and is of great significance for improving the durability and reliability of hydraulic excavator products.This thesis establishes the fatigue life evaluation model of excavator working device based on notch stress method,hot spot stress method and equivalent structural stress method,respectively,and applies them to evaluate the fatigue life of working device.The methods are verified by comparing their results with that of the bench fatigue test.The specific work is as follows:(1)The three-dimensional model of each component for the excavator working device is built in Solidworks.The finite element model of the excavator working deviceunder the bench fatigue test posture is built by Hypermesh,and then the finite element simulation is conducted in ANSYS.The stress distribution cloud figures of the working device is obtained,which provides a basis for the fatigue life analysis of the working device.(2)The method based on notch stress for fatigue life evaluation of excavator working device is studied.The virtual notch model of welded structure is established according to IIW standard,and then the notch stress spectrum of fatigue failure point is obtained.Finally,the fatigue life evaluation model based on the notch stress accoring to the IIW standard is established for the working device.(3)The fatigue life evaluation method of excavator working device based on hot spot stress method is studied,the hot spot stress extrapolation point of the fatigue evaluation position of the working device is determined,and the hot spot stress amplitude of the fatigue evaluation point is obtained according to the load-stress conversion coefficient at the hot spot.Based on the value spectrum,the fatigue life evaluation model of the working device based on the hot spot stress method is established based on the IIW standard.(4)The fatigue life evaluation method of the excavator working device based on the equivalent structural stress method was studied,six fatigue evaluation welds were determined,and the structural stress of each welding line node was calculated based on the Fe-safe Verity module,and the equivalent The structural stress method and the linear fatigue accumulation theory complete the fatigue life calculation of the welding seam of the working device evaluation,and establish the fatigue life evaluation model of the working device based on the equivalent structural stress method.(5)The fatigue life prediction software of the welding structure of the excavator working device is compiled.The software contains three modules: notch stress method,hot spot stress method and equivalent structural stress method.The fatigue life prediction function of the software is verified through examples.The fatigue risk positions of the working device obtained by the above three evaluation methods are all at the front end of the welding seam of the support plate for the buckets rod cylinder.The fatigue life is 6,672 hours,7,556 hours and 8,929 hours for the notch stress method,the hot spot stress method and the equivalent structural stress method,respectively.The comparison between the above three evaluation methods and the bench fatigue test results shows that the three methods established in this paper can predict the fatigue life of the excavator working device well.Among them,the equivalent structural stress method has the advantage of being insensitive to the grid,and a main SN curve is used to avoid the subjectivity of selecting SN curve.Therefore,the equivalent structural stress method is recommended to predict the fatigue life of excavator working device. |
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