Fatigue Models Based on Real Load Spectra and Corrected S-N Curve for Estimating the Residual Service Life of the Remanufactured Excavator Beam

Abstract

To more accurately predict the residual fatigue cycles and estimate the service life of the remanufactured excavator, the fatigue models integrating the corrected S-N curve, the RFC algorithm, the FEA model, and the mechanism dynamic model are established depending on the real load spectra under experimental working conditions and the corrected S-N curve of the beam metal remanufactured with the welding process. Depending on the test data of the unidirectional stress history and the servo displacements of the major cylinders, the mechanism dynamic model was first established to illustrate the real load spectra applied on the pivots of the working beam. The load spectra are further used in the finite element analysis (FEA) model to obtain the stress contours of the beam relevant to the sampling time, which is the stress spectra at any nodes on the beam in theory. Subsequently, the rain flow counting (RFC) algorithm based on the dual parameters of the cyclic stress amplitude and mean is established to provide the frequency spectra in the longevity region on the beam. Furthermore, due to the fatigue property changes of the beam metal remanufactured with the welding process, its S-N curve is corrected based on the detail fatigue rating (DFR) method to compute the stress cycles at each stress level on the crisis nodes. Finally, the total stress cycles that can be burdened by the remanufactured beam is computed under the Miner’s linear fatigue cumulative criterion. The total number of stress cycles is eventually converted to the fatigue and service life depending on the proportion of the sampling time under relevant working conditions. The results show that integrated fatigue models provide a practical approach to enhancing the accuracy of the estimation on the residual service life of the remanufactured excavator beam. It is significant for improving the reliability and safety of the remanufactured excavator.