Fragmentation-reconstitution metamaterial constructed from interconnected rotating triangular units and sub-units

This paper presents an innovative fragmentation–reconstitution (FR) mechanical metamaterial constructed from interconnected rotating equilateral triangular units, each designed to fragment into two right-triangular sub-units. Under tension, the equilateral unit splits into a pair of rotating sub-units, yielding a widely tuneable positive Poisson’s ratio. Under compression, the sub-units reconstitute into a single rigid equilateral unit, enforcing a constant negative Poisson’s ratio. Analytical models show geometric continuity throughout deformation, except for Poisson’s ratio discontinuity at the undeformed state, jumping abruptly from v12=1/3 in infinitesimal tension to v12=−1 in infinitesimal compression. This minimalist two-sub-unit architecture markedly simplifies fabrication over most quadrilateral-based FR systems, thereby allowing greater miniaturisation and lightweight designs while fully retaining rich functionality.