In-plane bidirectional quasi-static compression behavior of a novel multi-step star-isosceles triangular honeycomb

• A novel multi-step star-isosceles triangular honeycomb (SITH) was designed. • SITH is characterized by multi-step deformation in both directions, and its stress–strain curve has three plateau stages in Y direction. • The failure mechanism of the SITH and its energy dissipation mechanism are revealed. • This theoretical model can effectively predict the plateau stress and critical strain of the SITH are proposed. • The quantitative relationships between mechanical properties and various structural angle are established. Multi-stage plateau stress structures have recently attracted increasing attention for impact protection and energy absorption. However, most existing designs either provide limited in-plane energy absorption or exhibit multi-stage features only in one loading direction. To address the above-mentioned limitations, this research proposes a novel star-isosceles triangular honeycomb (SITH) structure. It combines the tunability of star-shaped geometries with the stability of triangular frameworks. The mechanical performance of SITH was systematically investigated through quasi-static experiments and numerical simulations. The results show that SITH provides excellent energy absorption in both directions under in-plane biaxial loading. Uniquely, it achieves three plateau stages in the Y direction. A theoretical model was formulated based on the deformation mechanisms that were observed. This model accurately predicts plateau stresses and critical strains. Parametric analyses of the key geometric angles further reveal their influence on the mechanical response. These insights support the optimization of structural performance. Compared with previously reported hybrid honeycombs, the proposed SITH structure demonstrates superior stability, tunable multi-stage energy absorption, and effectiveness in both loading directions. This work establishes a theoretical basis for design of star-shaped hybrid honeycombs. It also offers a promising strategy for impact protection in complex engineering environments.