In early fault diagnosis of hydraulic pump bearing, the fault characteristic signal is weak and the traditional envelope analysis is necessary and used to determined center frequency and bandwidth of the band-pass filter rely on experience, So a fault diagnosis approch based on empirical mode decomposition (EMD) and envelope spectrum is proposed. According to the method, the vibration signal collected from hydraulic pump is decomposed into some intrinsic mode function (IMF) using EMD at first. Then a few IMF is envelope analyzed and the envelope spectrum is obtained which include the main fault information. Finally, the working conditions and fault types of the pump bearing is determined by the analysis of the envelope spectrum. The experimental results show that the fault characteristics of the early hydraulic pump bearing is extracted effectively and three states of normal, inner ring failure and rolling element failure of pump bearing are correctly identified. It's an effective method for hydraulic pump bearing fault diagnosis.

The finite element model of integral wing panels with central penetration cracks under bending load was established, and the crack propagation process of the aircraft panel was simulated. The stress intensity factor (SIF) of the crack tip during crack propagation under varying conditions of crack length and panel structural parameters was determined. The effects of the panel structure parameters and crack size on the crack tip SIF were obtained. The regression analysis of the finite simulation element results has been performed and a regression model of SIF at the crack tip of the integral panel has been established, the determination coefficient of the regression model is 0.955.

Abstract:Reference stress statuses and the critical crack sizes are analyzed systematically and in detail for rectangle surface cracks in plates under combined endforce and cross-thickness bending loads via the 'global' reference stress method. The relationships of critical crack width and depth are obtained from the critical crack sizes analysis. Based on the net-section plastic collapse of the flawed component, a damage tolerance mathematical model for plates with single crack was built, which did not consider the contact of crack faces and it can be used for plates with a shallow crack or a deep crack under combined endforce and cross-thickness bending load. Using this mathematical model, the damage limits of aluminum alloy plates under different bending loads are obtained and a simplified damage tolerance model for aluminum alloy plates is established via regression analysis. The results obtained from the model and the regression model agree well with the experimental results especially when a/t<0.8. The test results show that the model can be fast and conveniently predict the damage limits for plates with surface cracks under bending.