A Reinforced Kite-Shaped Microstructure with Negative Linear and Area Hygrothermal Expansions

Abstract

Materials and structures are exposed to fluctuating temperature and moisture concentration, which alter their sizes; the capability to adjust the hygrothermal expansion, including into the negative region, permits greater control of hygrothermal stresses and strains. This paper introduces a type of 2D truss microstructure where each unit takes the shape of a kite with an additional reinforcing rod on the kite’s axis of symmetry. The coefficients of thermal and moisture expansions are positive in the direction parallel to the reinforcing rods, but linear negative hygrothermal expansion is obtained in the direction perpendicular to the reinforcing rods. The condition that gives areal negative hygrothermal expansion is also established, wherein this region is demarcated by the zero hygrothermal expansion line, which is attained when the inclined rods are perpendicular to each other.