A Negative Hygroscopic Expansion Material

Abstract

A negative hygroscopic expansion (NHE) material contracts with the absorption of moisture. This paper introduces an NHE microstructure based on a truss-like lattice system that consists of two types of conventional materials, namely the apex and base rods connected by hinge joints. Based on the analytical model for volumetric strains, NHE is attainable by controlling the dimensions, coefficients of hygroscopic expansion and the changes in the hygroscopic concentration in the apex and base rods. For the special case where the apex rods are rigid, NHE is attainable if the apex-to-base rod length ratio is less than 0.707; if the apex-to-base rod length ratio is greater than 0.707, NHE is still attainable if the base rod’s hygroscopic strain is sufficiently large. NHE materials and structures are envisaged to play an important role for countering the effects of thermal expansion so as to decrease the extent of hygro-thermal stresses and/or strains. As such, further investigations on NHE materials are recommended to facilitate design principles that minimizes stress and/or strains in extreme hygro-thermal environment.