Graded-twist TPMS metamaterial with twist-locking mechanism and non-monotonic stiffness

Triply Periodic Minimal Surfaces (TPMS) are increasingly exploited in additively manufactured metamaterials due to their smooth, continuous topologies that enable unusual mechanical behaviours. This paper proposes a graded-twist TPMS structure that undergoes continuous rotation along the height direction, leveraging its continuous topology to introduce a spatial gradient while preserving structural integrity. Through experiments and finite element simulations, the compression–torsion coupling behaviour is systematically investigated, revealing two deformation mechanisms, namely twist-locking and twist-release, and defining the compression–torsion coupling threshold (CTCT). In the twist-locking region, the graded twist enhances spatial constraints and optimises load transfer paths, transforming the deformation from layer-by-layer instability into globally coordinated deformation, thereby synchronously improving the stiffness, plateau stress, and specific energy absorption. Beyond the CTCT, the structure enters the twist-release region, where in-plane rotational degrees of freedom are activated, leading to a degradation of the mechanical properties. The CTCT of the Primitive structure is approximately 60°, whereas for the Gyroid structure, due to differences in surface connectivity, the effective CTCT is lower and the strengthening window is narrower. These mechanisms endow graded-twist TPMS structures with programmable mechanical responses based on geometric parameters, offering new strategies for multifunctional and intelligent structural design.