Search

Bolted joints are commonly used for assembling carbon fiber/resin composite structures. Since drilling may generate defects at hole edges which affect mechanical properties, it is of great engineering significance to develop proper repair methods to restore the mechanical properties of the defective parts. However, there are few studies on hole edge defects and their repair methods. Therefore, a novelty short fiber filling repair method was proposed to repair defective holes in this study. The mechanical properties of intact, defective and repaired countersunk composite joints were compared and investigated. Experimental tensile tests showed that defective joints had lower initial stiffness and failure loads compared to intact joints, while the mechanical properties were effectively restored after repair. Three-dimensional finite element models were also established to analyze the damage process of the joints. Results of numerical modelling were consistent with the experimental results. The simulations showed that changes in contact behaviors and local deformations caused by hole edge defects led to the low initial stiffness and stiffness transition point of the joint, while this phenomenon was reduced after repair. Additionally, despite different joint types, laminate failure mainly occurred around the hole and countersink.

Aerospace explorations stimulate extensive research on innovative propellant flow measurement technologies in microgravity conditions. Ultrasonic-based measurements have advantages of non-invasive and non-moving-component constructions as well as fast responses to bi-directional flow detection, its applications in aerospace explorations have already been reported. To avoid the shortages of pulse ultrasonic measurement configurations, flow measurement of continuous ultrasonic wave propagation is presented to match the requirements of large measurement range and high precision. Fabrication process and laboratory validations using water flow are presented. Ground experiments show that the linearity of the proposed ultrasonic flow meter is obtained in the measurement range [0, 80 ml/s] which is typical requirement in aerospace applications. Meanwhile, the fitted linear feature from the experimental data matches well the theoretical prediction except the flow prediction of stationary fluid. Under specific configurations, the absolute measurement error is significantly affected by the corresponding Reynolds number. Furthermore, the absolute measurement error is smaller when excitation signals with higher frequency are used if the phase tracking performance for different frequencies is identical.

Highly-performance fogdrop collection is of great practical importance in addressing the worldwide water shortages, especially in arid regions. Although great progresses have been made to solve this problem, there still are challenges in developing high-performance fogdrop collecting systems to satisfy efficient fogdrop capturing and fast transport simultaneously, which are two critical factors that determine the collection efficiency. The well-evolved water-collecting capacity of creatures that adapt to the harsh environment provides a great inspiration for the design of efficient collection systems. Here, inspired by the unique hierarchical structures and the excellent fogdrop collection ability of wheat awn, artificial awn-like hierarchical systems are developed via a precision 3D printing strategy which exhibit excellent fogdrop capture and fast transport. The presence of hierarchical structure composed of conical spine, gradient microgrooves, and oriented thorns enables the fogdrop collection to transform from dropwise mode on the thorns to filmwise one on the spine. Furthermore, the collection efficiency of such a bioinspired system is 5.90 g/cm−2·h, which is higher than individual ones and other bioinspired systems. Through the model of structure–function relationship, the mechanisms of diverse collecting behaviors are explored to address the origin of highly-performance collection. This work opens up new avenues to design systems and devices for dramatic fogdrop collection enhancement.

For airplane deicing problem, two dimensional electrothermal deicing model is established. The numerical study on heat transfer characteristics during electrothermal deicing process is presented. The Enthalpy-Porous Medium method is applied to describe the phase change process for the numerical simulation, which is a kind of enthalpy model. The computational domain is treated as a porous medium including solid ice and water liquid and mushy zone. The structured mesh topology is used to distribute the computational domain. The finite volume method is adopted to discretize the governing equations. The temperature is obtained by iteration of the energy equation coupled with the liquid volume fraction formula. The properties such as thermal conductivity of the mushy zone can be obtained by linear interpolation. The heat transfer characteristics are studied systematically for deicer pad including phase change process. The numerical study emphasizes on the effects of heating mode, cooling time, heater power and heater gap on phase change heat transfer characteristics. It shows that periodic heating mode for high heater power is superior to continuous heating mode for low heater power if reasonable combination of cooling time and heater power are adopted to obtain better deicing performance and less energy consumption. The existence of heater gap will decrease energy consumption less and make the temperature distribution more reasonable. Therefore, the reasonable distribution of heater gap can largely improve the deicing efficiency which is beneficial for the design of electrothermal deicer.