To improve the wear resistance of carburized 18CrNi4A steel used in aerospace transmission components with high-impact and heavy-duty conditions, DLC, TiAlN, and DLC/TiAlN coatings were deposited on carburized 18CrNi4A steel surfaces by magnetron sputtering. The surface and cross-sectional morphologies, chemical compositions, and mechanical properties of these coatings were characterized by SEM, XRD, nanoindentation, and micro-scratch tests. The tribological properties of carburized 18CrNi4A steel and these coatings with heavy-duty conditions of dry sliding, lubricant, and grease were investigated. In addition, TiAlN coatings were deposited on spline coupling teeth, and the anti-wear performance was investigated using a self-made spline coupling test rig. The results show that these coatings have lower coefficient of friction (CoF) and wear rate than carburized 18CrNi4A steel. DLC/TiAlN coating exhibits the lowest coefficient of friction and wear rate in aerospace synthetic lubricants (Mobil Jet Oil II) and molybdenum disulfide lithium grease (RIPP 7254), providing the best tribological properties. The wear mechanism of heavy-duty conditions with dry sliding, lubricant and grease were discussed. In addition, the TiAlN-coated spline coupling exhibited better wear resistance than the general spline coupling.

In this paper, a finite element model of the floating spline pair is first established, and the distribution of the contact pressure on the tooth surface of the spline with the axis and angular misalignment is analyzed. Then, the effects of axial misalignment and angular eccentricity on tooth fretting damage were evaluated, based on Ruiz fretting damage parameters. Finally, a floating spline wear fatigue damage model considering the wear effect is established based on the energy dissipation and critical plane SWT model, and the fretting fatigue cumulative damage distribution and life of the tooth surface under axial and angular misalignment are analyzed and evaluated. The results show that the misalignment of the axis makes the contact pressure distribution of each tooth uneven, and the RFFDP value of the most dangerous tooth is parabolic along the x direction, that is, serious fretting damage may occur at both ends of the tooth surface, and the crack initiation position on the tooth occurs near x/L=0. The angular misalignment makes the tooth contact only at one end edge, and the RFFDP value of the most dangerous tooth increases along the x direction, showing an exponential growth trend, reaching the maximum at x/L=1, and the crack initiation position occurs at near x/L=1. With the increase of axis or angular misalignment, the damage phenomenon of the floating spline tooth surface becomes more obvious, and the wear-fatigue life decreases sharply.

The teeth of misaligned spline couplings used in power transmission parts of helicopter and aeroengine often suffer serious abnormal wear faults during service. Through the self-made spline coupling test rig, the mechanism of misalignment on the spline coupling wear was explored. The tooth contact domain of the spline coupling with shaft misalignment is close to the addendum, and the tooth contact domain of the spline coupling with angle misalignment is mainly concentrated on the side of the tooth end. The edge contact effect becomes more serious as the amount of misalignment increases, resulting in abnormal wear at specific positions on the tooth surface. The presence of misalignment increases the vibration intensity of the spline coupling based vibration signal monitoring, which will increase the wear of the teeth. In addition, the difference in system vibration response of different misalignment types can be used to identify the misalignment failure mode of the spline coupling. It can be inferred from the characterization of wear debris that fretting wear is the cause of the failure of the misaligned spline coupling. Tooth modification, surface strengthening modification and lubrication design are necessary as potential solutions to improve the wear resistance of misaligned spline couplings.

In the assessment of internal ballistic performance reliability of Solid Rocket Motor (SRM), eigenvalue discriminance method has long been used. In order to avoid the limitations of the traditional methods, a curve similarity discriminance modification combined with Hausdorff Distance was introduced. A Monte-Carlo simulation model of internal ballistic performance was established, and several uncertain parameters were chosen. A sample analysis of performance reliability of a designed SRM was presented. The result was credible, which proved the modification is feasible and it can meet the needs of the assessment of the internal ballistic performance reliability.

Two-phase flow can have significance influence on exhaust plume of solid propellant, as well as the infrared radiation of the rocket. To show this influence, flow field of solid propellant rocket exhaust plume is simulated on different working conditions, where two-phase flow is involved using the DPM method. Comparing the flow filed results with or without two-phase flow considered shows that the existence of the condensed particles can decreases the velocity of the plume and increases the temperature. The influences of the flight height and Mach number on exhaust plume are also discussed.

To simulate a fully-coupled thermo-structure of a nozzle with adhesive failure, a flow field result is obtained based on a grid-independent check. The heat transfer coefficient along the nozzle is gained by Bartz formulation as an initial condition for thermo-structure simulation. A check for interface failure based on the adhesive, GD414, property is done to investigate the failure behavior, also to gain a simplified interface treatment. The gaps are chosen by experience. Then the simulation is carried out. The results show that gaps can release the stress of the interfaces while it can’t affect the whole stress distribution too much. The method is suggested to be used in the future and a more reasonable method is suggested.

A coupled fluid, thermal and structure analysis model was established for solid rocket motor nozzle. Based on a steady flow simulation and a transient thermal simulation, a transient structure analysis simulation was executed. The model took a frictional coefficient 0.3 into account to simulate a rub action between the parts of the nozzle. Result showed that with a frictional coefficient, Von Mises stress could be released which gives a constructive recommendation for a structure simulation of a nozzle. Also, the model was more close to the actual. A more dependable approach was introduced and it could contribute to designing department.

In aim to gain the capability of providing variable thrust, the technology of an axial pintle inserted into the nozzle of the solid rocket motor had been used. As the pintle inserted into the nozzle, the loss of specific impulse will increase. In order to reduce the loss of fluid dynamics of the pintle nozzle, considering the interaction of the nozzle contour and the pintle contour, CFD method combined with the response surface method is used to optimize the contour of the pintle nozzle. The central composite design is used to introduce a design point; the Kriging algorithm is used to generate the response surface; and the Nonlinear Programming by Quadratic Lagrangian is used for optimization. After the optimization, the loss of fluid dynamics can be reduced significantly. To study the influence of the key parameters to the loss of specific impulse, the key parameters are optimized independently in this paper. It indicates that the main factor of the loss of specific impulse is the parameters of the nozzle. To reduce the computational consumption, the process of optimization has been improved. And the result shows that when optimizing a pintle nozzle, the nozzle part and the pintle part can be optimized separately. The method that bases on the response surface not only takes into account of the interactive effects of the shape parameters, but also works with less calculation. Additionally it maintains the high accuracy and reliability. It can be used to select the optimal shape parameters of the pintle nozzle quickly, which has certain engineering application value.