Adaptive Twisting Metamaterials

Next-generation protective systems require adaptive materials capable of reconfiguring their response to impact type and severity, thereby offering multiple force-displacement pathways. Here, the study introduces twisting metamaterials, a subclass of architected lattices whose mechanics are captured by micropolar elasticity. Derived from twisting operations on primitive lattices, these structures exhibit geometry-induced torsional actuation and nonlinear responses, enabling adaptive crashworthiness. A multiscale predictive framework-combining Cosserat continuum mechanics, finite element modeling, and experiments-demonstrates its viability. Twisting sheet-based gyroid structures (10% relative density) are additively manufactured in FE7131 steel and tested under quasi-static and dynamic compression with varied torsional constraints, revealing adaptive energy absorption. When rotation is constrained, the structures achieve high axial stiffness (4.8 GPa), collapse stress (21 MPa), and specific energy absorption (15.36 J g^-1), while free-to-twist and over-rotation conditions reduce these values by up to 25%, 24%, and 33%, respectively. A macroscale model captures both axial and torsional responses, while SEM and µCT analyses of process-induced defects inform a parametric finite element study extended to 5% and 15% relative densities. Mapping their performance onto an Ashby chart highlights twisting metamaterials as a promising class of mechanically adaptive, crashworthy materials for advanced protection systems in automotive, rail, aerospace, and defence applications.