Cyclic Loading Response and Failure Mechanism of Composite Auxetic Perforated Buckling-Restrained Braces: A Comparative Study of Q235B and LY160 Steel

Auxetic materials and structures exhibit high energy absorption, vibration damping, and fracture toughness at the macroscopic level. Lightweight designs and perforated structures in buckling-restrained braces (BRBs) have garnered significant attention. However, existing auxetic cellular configurations remain relatively simplistic, with particularly limited options capable of synergizing with BRBs to achieve combined energy dissipation and seismic mitigation performance. This study introduces a novel composite auxetic cellular unit with a honeycomb structure of negative Poisson’s ratio and corresponding design method. The cellular unit is combined with a BRB to develop a new composite auxetic perforated BRB (NPR-BRB). Experimental and numerical simulation methods are used to investigate the effects of two core plate materials (Q235B and LY160), the reentrant angle, and the cross-sectional weakening rate of the composite honeycombs on the NPR-BRB’s performance under cyclic loading. In this study, four BRB specimens were fabricated, and the experimental results reveal that the fracture surface morphology (cup- and shell-shaped) depends on the deformation mechanism. One of the NPR-BRBs demonstrates stable hysteretic behavior, with an equivalent viscous damping ratio of 0.469 and a cumulative plastic strain of 219.7. Numerical simulations indicate that the LY160 BRB exhibits higher deformation capacity and energy dissipation, reducing stress concentration. The concavity angle has a negligible influence on performance. An increase in the cross-sectional weakening rate is correlated with a reduction in bearing capacity, hysteresis loop area, and compression–tension asymmetry, and an increase followed by a decrease in equivalent viscous damping ratio and cumulative plastic strain. The novel hybrid auxetic cellular units may enhance the energy dissipation performance of BRBs.