| As a large and complex agricultural machinery,corn harvester has many transmission parts and poor operating conditions,and the dynamic load produced in the operation seriously affects the reliability of the structure.As the main load bearing structure of corn harvester,the static stiffness and random vibration characteristics of the frame directly affect the reliability of the whole machine and the durability of the structure.Therefore,it is particularly important to understand the dynamic of the frame under actual working conditions and the random vibration characteristics of the frame for the performance evaluation and mechanism optimization of the whole machine.In this paper,the measured load spectrum characteristics and the static and dynamic characteristics of the frame are studied by combining the measured load analysis and finite element simulation.The main research contents are as follows:Firstly,on the basis of preprocessing the load test signal,the time-frequency characteristics of the load signal are analyzed,and the strength and vibration stability of the frame are preliminarily judged.In order to estimate the distribution of the load spectrum,a hybrid gaussian fitting method based on EM algorithm was proposed by using rainflow counting method to extract the load cycle.Secondly,the finite element model of the frame is established by analyzing the loading conditions and structural characteristics of the frame and discrete the frame with plate and shell elements.By analyzing the working condition of corn harvester,the stress distribution and displacement change of frame are simulated by mechanical analysis for two typical working conditions of bending and torsion.The results show that the frame structure meets the strength requirements.Thirdly,the prestressed modal analysis of the frame is carried out.Based on the analysis results,the power spectrum of the road surface excitation in the time domain is obtained by using Fourier inversion and road surface irregularity.The random vibration of the frame is analyzed.The influence law of speed on the stress response power spectral density of the node in dangerous position is revealed.Finally,based on the measured load-time series and the s-n curve of the frame material,the fatigue life of the frame was estimated by nCode fatigue analysis software.Based on the frequency response function of the frame and the frequency domain model of road roughness,the fatigue analysis of the frame in frequency domain is carried out,and the weak links of the frame are found out,which provides theoretical basis for the improvement and optimization of the frame structure. |
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