Windmill-shaped metamaterials achieving negative thermal expansion

Negative thermal expansion (NTE) metamaterials play a critical role in overcoming the limitations of traditional materials under thermal stress. In previous works, the author proposed windmill-shaped metamaterial exhibiting superior mechanical performance. However, its potential for thermal applications remains largely untapped. This study explores the design of windmill-shaped NTE metamaterials by incorporating bending-dominated and stretching-dominated deformation mechanisms, aiming to broaden their application scope and address challenges associated with conventional materials. Theoretical models were developed to derive the thermal expansion coefficients for these two distinct windmill-shaped metamaterials, and these models were validated through experimental and numerical methods. Additionally, the deformation modes and the effects of geometric parameters on the mechanical performance were also systematically analyzed. The findings reveal that geometric parameters play a pivotal role in tuning the thermal expansion behavior of the structure. By carefully tailoring these geometric parameters and material combinations, the thermal expansion coefficient can be adjusted across a wide range, from negative to positive values. This study introduces two novel windmill-shaped NTE metamaterials, providing critical insights and strategies to advance their engineering applications in fields requiring precise thermal management and structural stability.