Negative thermal expansion structures constructed from positive thermal expansion trusses

The negative thermal expansivity of a type of space frame structure is investigated herein. On the basis of space frame structure consisting of tetrahedral representative volume elements, a volumetric thermal strain, and a volumetric coefficient of thermal expansion (CTE) models are developed in this article for a special category of tetrahedron that is made from two types of materials, each for the three apex and the three base rods. Based on these models, the conditions for attaining negative volumetric thermal strain and negative coefficient of volumetric thermal expansion are established. Plotted results reveal a trend in which the extent of negative expansivity is increased for lower apex-to-base rod length and CTE ratios, and higher base rod CTE.