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Centrifugal impeller blades are prone to fracture failure due to crack propagation when rotating at high speed. Due to the complex blade geometry and load, there is an error in calculating the stress intensity factor of mode-I crack by formula. Due to the complex blade geometry and load, errors are generated inevitably in calculating the stress intensity factor of mode I crack using theoretical formulae. Although extended finite element method can be used to obtain stress intensity factors with good accuracy, the computation is generally time consuming, and sometimes hard to converge. Firstly, the stress intensity factors at the crack tips of the blade were simulated considering different crack start positions and crack lengths using ABAQUS's XFEM module, and their relationship with crack length and starting position was obtained. Next, the accuracy of the formulaic estimate on the stress intensity factor was tested based on the theory of fracture mechanics. Finally, a multi-layer back propagation artificial neural network (BP-ANN) with the stress intensity factor of the crack tip was established using the simulation results of the extended finite element method as the training data and the crack position and crack length of the blade as the input parameters. The example shows that the predicting accuracy of BP-ANN is better than that of the formulaic method. With the BP-ANN, the simulation times of the extended finite element method can be effectively reduced which is beneficial to promoting the application of fracture mechanics in the reliability design of centrifugal impellers. [ABSTRACT FROM AUTHOR]

The effect of Si addition on the microstructure and mechanical properties of Al-Mg-Si-Zn aluminum alloys were investigated. Results show that the microstructure of Al-Mg-Si-Zn alloy with low Si contents is mainly composed of Mg2Si and Mg5Si6 phases. With the increasing of Si content, Si and Al3.21Si0.47 phases precipitate in the form of eutectic phases in the alloys, at the same time, the mean shape factor of the second phase firstly increases and then decreases. Regression analysis results show that the Si content has the main influence and the mean shape factor has the least influence on tensile strength. Tensile strength increases significantly with the addition of Si, however, there is a remarkable drop in the elongation of the alloys. Decreased elongation is related to the formation of monotonous Al (200) structure and the enlargement of interplanar spacing of (111) and (200) crystalline planes.