The failures of high-voltage transformers and reactors can result from the deposition of copper sulfide on the oil-impregnated paper insulation. This study explored the influence of electric fields on copper sulfide deposition and the properties of insulating oils as a result of the reaction of dibenzyl disulfide (DBDS) with copper in oil-immersed transformers. Accelerated aging experiments were conducted for pig-tail windings under two sets of conditions, namely, thermal aging only at 140 °C and AC/DC electrical and thermal aging at 5 kV/140 °C under low oxygen condition. This was combined with oil containing dibenzyl disulfide (DBDS) added to the non-corrosive oil to a concentration of 200 mg/kg. The corrosive sulfur deposits were examined by observing the surface morphology of the windings and measuring the copper and sulfur contents on the windings via inductively coupled plasma-atomic emission spectrometry and a precipitation method. The properties of the insulating oils were measured and analyzed at intervals. The results indicate that electric fields increased the amount of deposited copper sulfide on the windings. The higher the electric field strength, the higher the amount of deposited copper sulfide on the insulating paper surface. Subjecting the oil-paper insulation to electric field and elevated temperature generates dissolved copper in the insulating oil. The electric field can promote the dissolution of copper in oil. The ageing oil under thermal and electrical stresses promote copper dissolution and increase corrosion rate.

Wear is one of the main failure causes of hydraulic seals. Wear will lead to degradation in the mechanical properties and sealing properties of seals. Compared with hydraulic seals with one-way rotational motion, the hydraulic reciprocating rotary seals work in more complex operating conditions, so their wear mechanism becomes more complicated. Aimed at exploring the friction and wear law of hydraulic reciprocating rotary seals and the property evolution law during the wear process, this paper set up an experimental system to simulate the working conditions of the hydraulic reciprocating rotary seals. The friction characteristics were obtained under different working pressures and different motion parameters. The wear characteristics were obtained under rated working conditions. The surface morphology was observed by SEM and the wear mechanism was analyzed.

Most of the leakage faults in hydraulic pipeline systems occur in the pipe joint. The research on the high-pressure sealing and reliability of the pipe joint is very important in the application of civil aircraft parts. On the basis of studying the characteristics of pressure pulsating fluid, this paper explores the influence of a high pressure pulsating fluid on the sealing performance of flameless extruded pipe joints and analyzes the influence of the internal fluid pulsating amplitude and fluid under different pressures on the contact stress distribution of the sealing surface of the pipe joint. The results show that with the increase in flow pulsation amplitude from 0.5% to 5%, the amplitude of contact stress on the sealing surface decreases with creep time, which makes the sealing performance better. However, the effective working time of the joint as a whole decreases from 2000 to 194 h. The high-stress area of the contact surface expands as the fluid pressure increases, and the high internal fluid pressure obviously improves the sealing effectiveness and reliability of the pipe joint. In addition, the influence of fluid pulsation amplitude on the leakage rate of the joint is much greater than that of the fluid pressure.

The multi-random-effects gamma process has a better characterization effect for degraded data with individual differences. In this paper, a reliability evaluation method for gamma stochastic processes with multiple random effects is studied. The mathematical model of multiple random effects gamma process was established. The model parameters estimation method was established based on the Bayesian approach. The prior distribution acquisition method was discussed, and the parameters of the multiple randomeffects gamma process were estimated by the MCMC-Gibbs method. The correctness of the model and method was verified by numerical simulation, the influence of algorithm parameters on the algorithm solving process was studied. In the fourth part, the reliability of aviation hydraulic rotary joints was studied by using multiple random effects gamma processes.

The formation of a scale on a compressor blade surface is inevitable, and the study of the distribution of the scale can provide effective guidance for the cleaning of a wing engine. Using the waste liquid collected from the engine during the wing water washing process as a data sample, the main components of compressor blade surface fouling were analysed, which included 49.9 SiO₂, 14.5 FeO, 11.5 Al₂O₃, 9.4 CaO, etc. Based on JKR contact theory, a model for calculating the total thickness of the fouling layer on the blade surface was established. Through a simulation experiment on the fouling of a blade surface, the number of particulates deposited on the pressure surface was lower than the amount of the secondary deposition mass on the suction surface. From contrastive analysis of the results of perforation, the fouling is divided into three types: loose, dense, and transitional. The surface of a single blade can be divided into four different fouling areas. The parameters of the engine cleaning process can be designed according to the characteristics of the fourth area.

To study the influencing factors of liquid droplets on the cleaning effects of the scale layer, a three-dimensional droplet-impacting-a-blade model is constructed. The finite volume method and the volume of fluid method are used to numerically study the dynamic characteristics of a droplet impacting the fouling layer of a blade. The results show that under certain conditions, increased velocity and diameter of the droplet lead to an increase in the impact force of the droplet, and the greater the curvature of the blade surface, the smaller the vertical impact force of the droplet; likewise, the greater the impact force on cutting, the larger the corresponding spreading coefficient. The impact of liquid on the surface of the blade reduces the peak value of the droplet impact force. Finally, the increase in droplet diameter and velocity will improve the cleaning effect of the jet droplet. The larger the blade surface curvature, the wider the droplet cleaning area will be.