This study uses the classical Flügge shell theory and homogenization transformation method to predict the critical pressure of functionally graded material (FGM) cylindrical shells under hydrostatic pressure. The method considers the similarity in physical properties and mechanical behavior between FGM and uniform materials. The vibration equation of the coupled system of an underwater FGM cylindrical shells is derived using the wave method, taking into account the influence of fluids. The natural frequency of the FGM cylindrical shell under hydrostatic pressure is obtained using the Newton iteration method. Based on the linear correlation between critical load and load level with zero natural frequency, the fitting curve method and the formula method after homogenization transformation are used to predict and analyze the critical pressure of FGM cylindrical shells under hydrostatic pressure. The effects of various parameters on the critical pressure are discussed. The results show that the material elastic modulus E, geometric dimensions h/R and L/R of FGM cylindrical shells, and different boundary conditions have a significant impact on the critical pressure. Through multiple comparative analyses of examples, the correctness and effectiveness of the proposed method are verified. The method has high prediction accuracy and low computational cost, providing a new exploration path for the analysis of non-uniform structural mechanical behavior.

As functionally graded material (FGM) plates are widely used in engineering and industrial fields, the fracture strength evaluation of the cracked FGM plate becomes increasingly important. However, due to the gradation of the mechanical properties of FGM, few analytical methods are simple and available. In this paper, a convenient strength evaluation method for the cracked FGM plates under different loadings is proposed in terms of the stress intensity factor (SIF) appearing at a crack tip. This method uses the stable relationship of singular stress fields between FGM and homogeneous material to greatly simplify the complex SIF calculation process of the cracked FGM plate. The results show that the SIFs of FGM plates under tension, bending, and three-point bending (experiment) can be obtained conveniently and accurately by using two simple formulas, and the trends of critical SIF can also be investigated directly even if the SIF solution of the homogeneous plate (reference problem) is unknown. Comparisons with the published theoretical and experimental results indicated that the present method is reliable, precise, and practical to determine SIF and perform strength prediction.

This paper proposed an energy method, based on the Donnell thin shell theory, to derive the vibration characteristic equations of underwater ribbed and ring-stiffened functionally graded (FG) cylindrical shells, and the characteristic equations are solved by MATLAB to obtain their natural frequencies. Through comparative analysis with the existing literature, the correctness and effectiveness of the calculation method are verified. By using numerical examples, the effects of the shell size, material composition, rib section length to width ratio, and rib arrangement on the natural frequency are analyzed, and it has been proved that the aforementioned parameters are the key parameters influencing natural frequency. It is found that the natural frequency of the FG cylindrical shell increases with the decrease in the length–diameter ratio of the shell, increases with the increase in the shell thickness–diameter ratio, and increases with the decrease in the rib spacing. When the cylindrical shell is short and thin, the addition of longitudinal ribs can significantly change the natural frequency of the cylindrical shell.

The interconnecting joint of space cables get smaller and smaller, when the installation space of assembly is smaller, which is easy lead to wire stress and wire breakage. The purpose of encapsulating of the connector is to protect the cable interconnecting, including crimping and soldering joints, and to reduce the weight of the cables at the same time. In this study, the connectors were injection molded, potted without back shells, and potted with back shells in extravehicular cables. The space accelerated tests including mechanical vibration, mechanical impact, bending, and temperature cycle tests were performed on encapsulated cables. The study on tensile strength, metallography, and Scanning electron microscopy (SEM.) of the interconnecting joints showed that, the electrical performance was good with all three kinds of encapsulating process. Crack and delamination defects were not found in the interface of soldering or crimping joint. The three encapsulating method can effectively protect the interconnecting joint of space cable.