A skin structure for thermal protection is one of the most interesting components that needs to be considered in the design of a hypersonic vehicle. The thermal protection structure, if a dense structure is used, is heavy and has a large heat conduction path. Thus, a lightweight, high strength structure is preferable. Currently, for designing a lightweight structure with high strength, natural materials are of great interest for achieving low density, high strength, and toughness. This paper presents bio-inspired lightweight structures that ensure high strength for a thermal protection system (TPS). A sinusoidal shape inspired by the microstructure of the dactyl club of Odontodactylus scyllarus, known as the peacock mantis shrimp, is presented with two different geometries, a unidirectionally corrugated core sandwich structure (UCS) and a bidirectionally corrugated core sandwich structure (BCS). Thermomechanical analysis of the two corrugated core structures is performed under simulated aerodynamic heating, and the total deflection and thermal stress are presented. The maximum deflection of the present sandwich structure throughout a mission flight was 1.74 mm for the UCS and 2.04 mm for the BCS. Compared with the dense structure used for the skin structure of the TPS, the bio-inspired corrugated core sandwich structures achieved about a 65% weight reduction, while the deflections still satisfied the limits for delaying the hypersonic boundary layer transition. Moreover, we first fabricated the BCS to test the thermomechanical behaviors under a thermal load. Finally, we examined the influence of the core thickness, face-sheet thickness, and emittance in the simulation model to identify appropriate structural parameters in the TPS optimization. The present corrugated core sandwich structures could be employed as a skin structure for metallic TPS panels instead of the honeycomb sandwich structure.

The piezoelectric hybrid actuator is a new electro-hydrostatic actuator with broad prospects for development. Compared with the traditional hydraulic pump, the piezoelectric hybrid actuator is characterized by a simple structure, small size, lightweight, and low power. However, it has a well-known weakness: It produces only a small actuation force and then cannot be used in real applications. Because the maximum force produced by a one-piezoelectric pump design cannot be increased much due to limitations in the power supply and piezoelectric materials, researchers have moved to the use of multiple piezoelectric pumps. In this research, a double-piezoelectric pump-hydraulic cylinder hybrid actuator was designed, manufactured, and tested in order to increase the actuation force. Key design factors such as the connection method and driving method were investigated to realize the double-piezoelectric pump design and achieve a high level of performance. A total of three kinds of double-piezoelectric pump-hydraulic cylinder hybrid actuator designs were selected by a theoretical approach and implemented using two identical piezoelectric pumps. A manual valve system was installed for switching the connection method (series and parallel modes). The driving method, phase, or voltage was controlled by a LabVIEW program. The maximum blocking force of 4615 N was measured at 250 Hz for cross driving, series connection and φ30-mm cylinder. The maximum velocity of 68.3 mm/s was measured at 300 Hz for cross driving, series connection and φ21-mm cylinder. Fluid structural interaction analysis using ANSYS software confirmed the experimental results. The performance of double-piezoelectric pump-hydraulic hybrid actuator meets the minimum requirements for mechanical and aerospace actuator applications.