Damage evaluation of regolith-resin-composite (RRC) materials for lunar structures using linear and nonlinear ultrasonic waves

The growing interest in establishing permanent bases on the moon necessitates the development of durable construction materials that can withstand the extreme lunar environment. Even minor damage from repeated loading, material aging, and harsh conditions can disrupt the controlled internal environments that lunar structures create and thus pose serious threats to potential human inhabitants. Non-destructive inspection is essential for ensuring a safe and secure habitat. Although the ultrasonic wave technique is a commonly used non-destructive inspection method, the behaviour of ultrasonic waves in extraterrestrial construction materials has not been fully explored. This paper investigates the viability of ultrasonic waves and their performance for non-destructive evaluation in a novel material fabricated using lunar regolith simulant and epoxy resin, known as regolith-resin-composite (RRC). An experimental framework is employed that comprises nine loading stages, each of which involves applying a load at a specific percentage of the material's ultimate capacity, followed by unloading. Subsequently, the linear and nonlinear characteristics of the ultrasonic wave are investigated at the end of each stage. Linear ultrasonic parameters, such as wave velocity and amplitude and a relative nonlinear ultrasonic parameter are then derived by analysing the received signal. All ultrasonic parameters are presented in relation to increasing compression load on RRC samples. The results indicate that the relative nonlinear parameter increases by 76 % at the maximum applied load. In comparison, the maximum change of the linear parameter (amplitude) corresponding to that load is 19.9 %. Thus, the second harmonic generation is highly sensitive to damage progression and exhibits distinct values at different loading stages in the RRC, thereby signifying the reliability of ultrasonic waves for inspecting lunar construction materials. • Linear and nonlinear ultrasonic responses of Regolith-resin-composite (RRC) are investigated to evaluate damage. • Experimental studies are carried out under controlled compressive loading. • The nonlinearity parameter is derived from the frequency and time-frequency domains. • Second harmonic generation effectively monitors damage progression in RRC materials. • The nonlinearity parameter is more sensitive to damage than the linear parameters.