| The hydraulic cylinder of wheel loader is a key component for shoveling and transporting. The phenomenon of impact loads and fatigue failure of hydraulic cylinder frequently happens due to the complicated and variable conditions. As a result, it leads to serious economic losses. Load spectrum, which is the foundation of fatigue analysis, anti-fatigue design, and prediction of the fatigue test, is put on agenda. In accordance with the topic of "Wheeled Vehicle Load Spectrum Transmission key technologies" (50805065) aided by National Natural Science Fund project, a novelty compiling method of load spectra and reconstruction in time domain were proposed. Subsequently the load spectra were validated to predict the fatigue life on finite element model of hydraulic cylinder on wheel loader.In this paper, the work and conclusions are as follows:1. The fatigue mechanism of hydraulic cylinders is analyzed and the development of load spectrum is reviewed. Based on the present research situation of load spectrum, the significance of compiling load spectrum of hydraulic cylinder for wheel loader, as well as the reconstruction of time-domain signal, were explicit in this paper.2. Testing scheme is determined, then the measured load time history is preprocessed.Testing procedure of load time history for hydraulic cylinder has been normalized in the domain of road conditions, of the drivers'operations, of the procession route, and of the materials preparation. The necessary data preprocessing has been carried out by filtering the small load cycles and eliminating the spikes. Combing with the cyclical working characteristics of wheel loader, we put forward a sectioning method to process tested load time history. Based on the load data of each section, statistical analysis and stationary test were performed. The results showed that: load time history of each operating section meet the stability test requirements.3. Extrapolation of the load spectra and acquisition of the design spectra.Firstly, on the basis of the first extreme theory, the mathematics model of the extreme value was established by POT method. And the corresponding extrapolated factor was calculated in the GPD model. Then the extreme loads were obtained by MATLAB programs and cycles were revealed by rainflow counting method. Finally the design load spectra of hydraulic cylinder in the total load cycles were compiled.4. Reconstruction of load time history in time domain.Some large load cycles were destroyed when dividing the operating cycles into four working sections. So it may lead to some statistical errors if we ignore them. The Markov chain theory has the ability to reconstruct the missed cycles in each section. So we used Markov chain to calculate and reconstruct the large load cycles. By comparison, the reconstructed load time histories of hydraulic cylinder have the same distribution characteristic with the measured load time histories.5. Fatigue analysis of finite element model for hydraulic cylinders.The finite element model of hydraulic cylinder of wheel loader was established. Under the static strength, stiffness and stress behavior of the tube body was analyzed and the critical section of hydraulic cylinder is fixed. Loading the load spectra of each section on the finite element model of hydraulic cylinder, the fatigue damage and the fatigue life of each working section were calculated under the hazardous location.A complete process of compiling load spectra of hydraulic cylinder was proposed in this paper, including selection of testing conditions, preparation of the materials, pretreatment of sample data and calculation of the extreme load. Also the reconstruction of the load spectra, based on the Markov theory was illustrated by an empirical example. This paper provided referential basis for compiling load spectra and reconstructing the time load history in time domains on hydraulic cylinders.
|
PDF Full Text Request