In situ study on the hierarchical interfacial “global regulation – equilibrium iteration” bearing-toughening mechanisms in Strombus gigas shell by synchrotron radiation computed tomography technique

•3D crack evolution of Strombus gigas shell’s hierarchy structure was studied by SR-CT.•First-order interface can adjust the global stress distribution and failure mode.•Stress regulating mechanism of 2nd and 3rd order interfaces adjust crack propagation.•“Iterative, gradually balanced” of multistage interfaces ensure excellent toughness. Strombus gigas shell is a natural biological composite material with excellent strength and toughness, and its excellent performance is closely related to its cross-laminated multistage structure. Studying the damage evolution process to reveal the strengthening mechanism is very important. Through synchrotron radiation computed tomography experiments, the important damage evolution phenomenon from outside to inside of the whole structure, from single interface to multistage interfaces (i.e. first-order, second-order and third-order interfaces), were observed. The first-order interface plays the role of global regulation of stress distribution and failure mode in the whole structure, and the second-order and third-order interfaces play the role of regulating stress distribution during crack propagation. These interfaces cooperate with each other while playing respective roles, showing the optimization and control mechanism of “iterative to balance”. New comprehensions of multistage interfaces are expected to provide new strategies for the optimization design and manufacturing of artificial composite materials.