High-pressure hydrogen tanks which are composed of an aluminum alloy liner and a carbon fiber wound layer are currently the most popular means to store hydrogen on vehicles. Nevertheless, the aluminum alloy is easily affected by high-pressure hydrogen, which leads to the appearance of hydrogen embrittlement (HE). Serious HE of hydrogen tank represents a huge dangers to the safety of vehicles and passengers. It is critical and timely to outline the mainstream approach and point out potential avenues for further investigation of HE. An analysis, including the mechanism (including hydrogen-enhanced local plasticity model, hydrogen-enhanced decohesion mechanism and hydrogen pressure theory), the detection (including slow strain rate test, linearly increasing stress test and so on) and methods for the prevention of HE on aluminum alloys of hydrogen vehicles (such as coating) are systematically presented in this work. Moreover, the entire experimental detection procedures for HE are expounded. Ultimately, the prevention measures are discussed in detail. It is believed that further prevention measures will rely on the integration of multiple prevention methods. Successfully solving this problem is of great significance to reduce the risk of failure of hydrogen storage tanks and improve the reliability of aluminum alloys for engineering applications in various industries including automotive and aerospace.

Fiber metal laminate (FML) is a kind of lightweight material with excellent mechanical properties combining advantages of metal laminates and fiber reinforced composites. It has been widely used in the aerospace and transportation fields and is especially used as structural material such as aircraft skins, wings, and tails. However, under complex service conditions, interlaminar failure in FMLs greatly reduced mechanical properties of the material, even leading to serious economic and safety disasters. The failure and destruction of important structural parts of aircraft and other manned transportation vehicles are extremely unsafe for people. Therefore, it is of great significance to summarize the interlaminar failure behavior of FMLs and find ways to avoid these defects. This review paper is a collection of various researches done by many groups, which systematically discuss the interlaminar failure behaviors and their control methods of FMLs. The application status of several common FMLs in aircraft structures was given. The common interlaminar failure modes of FMLs and the testing and evaluation methods of interlaminar properties were stated. The failure mechanisms and the corresponding control methods were analyzed. Finally, the future developments of FMLs were also discussed by the authors. Through this review article, readers can obtain new research progress about the control method, the mechanism and future development on the failure behavior of FMLs in a more efficient way.

Adhesive bonding is widely used in the joining of metals and carbon fiber-reinforced plastics (CFRPs). Ultrasonic vibration was used to improve adhesive bonding of CFRP/Al alloy joints grafted with silane coupling agent, and the effect of the ultrasound on the bonding was studied. The surface of Al alloy was treated with a silane coupling agent, and then the ultrasonic vibration was applied on the adherend during the adhesive bonding process. The shear strength was tested, and the mechanism was analyzed by scanning electron microscope (SEM) and Fourier transform infrared spectrometer (FTIR). It is found that the ultrasonic assisting can further promote the bonding of the Al alloy and the adhesive. For the test joins, the shear strength was increased by 267.50% using the silanization treatment plus the ultrasonic assisting. The ultrasonic assisting promoted the grafted epoxy group to react with the adhesive more sufficiently at the Al/adhesive interface by causing micro-mixing and intensified molecule collision, and thus more chemical bond was formed. Under the ultrasonic action, the interface and the adhesive layer became tighter owing to the impact contact at the interface and the oscillating flow in the adhesive layer. The ultrasonic vibration assisting increased the bonding strength by promoting the chemical bond and improving physical morphology.

Ultrasonic curing is an effective way to enhance the curing extent of composite material bonding in the aerospace industry. The non-thermal effect of ultrasonic has been revealed to improve curing efficiency. However, the mechanism of the ultrasonic non-thermal effect is still not clear. In this work, a variable activation energy model of ultrasonic curing was established by utilizing the iso-conversional method, including the activation energy of the thermal effect and activation energy of the non-thermal effect. The thermal effect caused by ultrasonic was accurately peeled off. An obvious decrease in activation energy was found from 54 kJ/mol in thermal curing to 38 kJ/mol in ultrasonic curing. The activation energy of the reaction system in ultrasonic curing was substituted into the modified Kamal autocatalytic equation, and the parameters of the ultrasonic curing kinetic model were estimated by means of an ALO algorithm. Further discussion based on in situ FTIR showed that the non-thermal effect of ultrasonic can affect the vibration strength, stability, and chemical bond energy of internal groups, but cannot cause the fracture of chemical bonds. Moreover, frontier molecular orbital analysis showed that the chemical reactivity of epoxy/amine molecules increased and the HOMO–LUMO energy gap decreased from 6.511 eV to 5.617 eV under the effect of ultrasonic.

Traditional thickness-prediction methods underestimate the actual dome thickness at polar openings, leading to the inaccurate prediction of the load-bearing capacity of composite hydrogen storage vessels. A method of thickness prediction for the dome section of composite hydrogen storage vessels was proposed, which involved fiber slippage and tow redistribution. This method considered the blocking effect of the port on sliding fiber tows and introduced the thickness correlation to predict the dome thickness at polar openings. The arc length corresponding to the parallel circle radius was calculated, and then, the actual radius values corresponding to the bandwidth were obtained by the interpolation method. The predicted thickness values were compared with the actual measured thickness. The maximum relative error of the predicted thickness was 4.19%, and the mean absolute percentage error was 2.04%. The results show that the present method had a higher prediction accuracy. Eventually, this prediction method was used to perform progressive damage analysis on vessels. By comparing with the results of the cubic spline function method, the analysis results of the present method approached the actual case. This showed that the present method improved the accuracy of the design.

All solid-state lithium-ion batteries based on polymer electrolytes have higher safety and energy density, but the low conductivity of lithium ion restricts its application. This study proposes a new method to promote the ionic conductivity of polyethylene oxide (PEO)-based solid electrolytes. In this method, the PEO-based solid electrolyte was first prepared by casting, and then power ultrasound was exerted on the electrolyte by a sandwich structure to modify the electrolyte structure. Through analysis of the performance and microstructure of the electrolyte, it was found that the ultrasonic treatment increased the ionic conductivity by 78%, improved tensile strength and plastic deformation ability, but did not affect the thermal stability and the chemical composition. The ultrasonic vibration, exerting high energy to the solid electrolyte through high-frequency vibration, broke PEO grains and melted them with the frictional heat at boundary. Due to the slight melting and fast solidifying produced by the pulsed ultrasonic treatment, the crystallization was suppressed. The crystallinity was thus reduced by 6.2%, which increased the migration channels of lithium ions and reduced the tortuosity effect. Furthermore, the ultrasonic vibration compressed the electrolyte to produce plastic flow of the material, which made the electrolyte structure more compact. The density of ethylene oxide (EO) units thus increased in the amorphous phase, providing multiple electron-donor coordination sites for the Li⁺. The hopping distance of the ion between donors decreased, which also facilitated the migration. In addition, the mechanical performance of the electrolyte membrane improved. This study provides a reference for the improvement of polymer based all-solid-state batteries.