Ultimate bearing behavior in the post-buckling stage of composite pressure hulls based on new detection methods

Abstract

This study employs novel testing methods and analysis techniques to investigate the ultimate load-bearing characteristics and failure mechanisms of composite thin-walled pressure hulls. An analytical model based on the classical laminated plate theory, incorporating the Hashin damage failure criterion, is developed to determine their ultimate bearing capacity. Five carbon fiber cylindrical shells are manufactured to validate the failure mechanism and evaluate the model's predictions. Deep-sea pressure testing and ultrasonic testing are conducted on these shells. The resulting data is analyzed using both macroscopic and microscopic approaches to gain insights into their load-bearing behavior and failure mechanisms. The study demonstrates the significant influence of the thickness (t) to radius (R) ratio on the ultimate load-bearing capacity of these composite thin-walled pressure hulls. Failure primarily arises from compression failure in both the matrix and fibers. The load-bearing process encompasses uniform shrinkage, critical buckling, and post-buckling states. Material failure primarily occurs during the post-buckling stage, while no damage occurs during the initial buckling. On a microscale, failure at the interface between the fibers and matrix is identified as the primary contributor to overall structural failure. Enhancing the fracture energy of the interface is recommended to enhance the ultimate load-bearing capacity of the hulls.