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This study focused on the fatigue and corrosion fatigue of maraging steel 18Ni (250). The 18Ni (250) samples were tested for axial fatigue in air and 3.5% NaCl solution. The effects of loading frequency and stress ratio on the fatigue strength of 18Ni (250) were studied. In air, the loading frequency was 10 Hz, and the stress ratio was 0.5. However, three loading methods were used in the 3.5% NaCl solution: (i) the loading frequency of 1 Hz and stress ratio of 0.5; (ii) the loading frequency of 1 Hz and stress ratio 0.1, and (iii) the loading frequency 5 Hz and stress ratio 0.5. The corrosion fatigue strength of samples in the 3.5% NaCl solution was 63.3% lower than that of the samples in air. The fractures in the samples were observed after the test.

This study focused on the fatigue and corrosion fatigue of maraging steel 18Ni (250). The 18Ni (250) samples were tested for axial fatigue in air and 3.5% NaCl solution. The effects of loading frequency and stress ratio on the fatigue strength of 18Ni (250) were studied. In air, the loading frequency was 10 Hz, and the stress ratio was 0.5. However, three loading methods were used in the 3.5% NaCl solution: (i) the loading frequency of 1 Hz and stress ratio of 0.5; (ii) the loading frequency of 1 Hz and stress ratio 0.1, and (iii) the loading frequency 5 Hz and stress ratio 0.5. The corrosion fatigue strength of samples in the 3.5% NaCl solution was 63.3% lower than that of the samples in air. The fractures in the samples were observed after the test.

The water-air amphibious vehicle,a kind of vehicle that can operate both in water and air, has been a hot topic of recent research for its potential wide application prospects in military and civil fields. To better understand the design requirements of this kind of water-air transmedia vehicles,the characteristics of vehicles in different media are introduced including the aircraft,the surface ship and the submersible. Then a brief analysis is made to compare these three kinds of vehicles and summarize the possible characteristics of water-air transmedia vehicles. According to the flight structure,the current water-air amphibious vehicles are divided into three categories:fixed-wing vehicle,rotorcraft and bionic vehicle and the typical prototypes of each category are reviewed. Finally,the key technologies and challenges are discussed.

The Local Characteristic-scale Decomposition（ LCD） and the Local Mean Decomposition（ LMD） are two kinds of effective adaptive time-frequency analysis methods which widely used in the field of rotating machinery fault diagnosis. In order to compare the difference of calculation process and the performance of them,aiming at the acquiring of mean curve and decomposition termination conditions,the comparative research are carried out. The deficiencies of LMD in the mean point definition,interpolation method and pure frequency modulation standards are pointed out. Through the simulation signal and the bearing inner ring fault vibration signal analysis,the superiority of LCD is verified,but the part of the mind of LMD can also provide reference for the LCD.

Aiming at diagnosing the fault of roller bearing accurately,a method based on Local Characteristic-scale Decomposition（ LCD） and Base-scale Entropy（ BE） is proposed. Firstly,the rationality of using the BE to extract the fault information of the bearing vibration signal is analyzed,according to the parameter selection problem of BE,a method based on phase space reconstruction theory is proposed,and the delay time and embedding dimension are selected. Secondly,in order to extract the fault feature fully,a kind of adaptive multi-scale BE based on LCD is proposed. Finally,the denoising signal and the useful components of LCD are selected to compute the BEs as the feature vector of support vector machine（ SVM） to fault diagnosis. The analysis of the bearing fault data shows that the method can identify the normal,inner ring fault,outer ring fault and rolling fault effectively.

As a new self- adaptive time- frequency analysis method,the local characteristic- scale decomposition（ LCD） is proposed lately and applied to mechanical fault diagnosis. The influence of noise to LCD is studied and a new fault diagnosis based on singular value decomposition（ SVD） de- noising and local characteristic- scale decomposition is proposed. Firstly,the phase space reconstruction of original vibration signal is carried out,and then,the noise is effectively eliminated by using singular value decomposition. The LCD of the de- noising signal is carried out and some intrinsic scale components（ ISC） are acquired,then the envelope spectrum analysis on the ISCs is carried out and the fault feature is extracted. Through the analysis of the simulation data and the bearing fault data,the effectiveness of this method is verified.