Negative Thermal Expansion Realized by an Incomplete Bimaterial Ring

Incomplete bimaterial ring (a circular ring with a gap) capable of producing negative macroscopic thermal expansion is proposed and its behavior is analyzed. The ring exhibits negative thermal expansion (NTE) (in the plane of the ring) when the outer ring has higher thermal expansion coefficient than the inner one. When the thermal expansion coefficients are equal (monomaterial incomplete ring), the effective (macroscopic) planar thermal expansion becomes zero. (The complete thermal expansion will be positive but small.) It is the presence of the gap which is the basis of this thermal behavior. Similar effect can be achieved by spring or spiral structures where the role of the gap is played by the open ends. These structures will have higher stiffness than the incomplete bimaterial ring. The thermal expansion of the ring is characterized by the effective (macroscopic) coefficient of linear thermal expansion. The effective coefficient of linear thermal expansion depends on the temperature increase, making the thermal expansion nonlinear. Planar and 3D NTE structures are considered. Incomplete bimaterial ring (a ring with a gap) exhibits negative thermal expansion (in the plane of the ring) when the outer ring has higher thermal expansion than the inner one. It is the presence of the gap which is the basis of this thermal behavior. Similar effect can be achieved by spring or spiral structures where the gap is replaced by the open ends.image (c) 2024 WILEY-VCH GmbH