Bimaterial lattices with anisotropic thermal expansion

Numerous structures that are used in the aerospace and automobile industries, microelectronics, and civil engineering are subject to large variations of temperature. The deformations caused by temperature can be dangerous because they lead to thermal stresses and failure if materials with mismatched thermal expansion are joined. On the other hand, thermal extensions can be used to achieve desirable displacements in structures. In this work, we use bimaterial lattices made of two materials and empty space that combine low weight with high stiffness and structural robustness. The lattices can serve as adapters that eliminate or mitigate dangerous thermal stresses, as elements for fine tuning in optical systems, or as thermal actuators. To perform these functions, the lattices must be anisotropic, which can be achieved if the lattice consists of non-identical anisotropic cells. Each cell is composed of an irregular triangle made of one material surrounded by a skewed hexagon made of another material. The overall performance of the lattice is defined by six hexagon skew angles and the ratio of the two coefficients of thermal expansion (CTEs) of the lattice materials. The cells are connected to adjoining cells at three points; changes in the distances between these points as a function of temperature can be tailored. The primary goal of the research is to elaborate general principles and algorithms to design lattices, select material, and improve structural efficiency. Several adaptive lattices are designed including a polygonal ring connector to prevent distortion in cylindrical optical components, a lattice preventing shaft and collar sticking, and lattices controlling the total deflection of two substrates. Lattices providing predetermined displacements in desirable directions have been studied, and it was demonstrated that different temperature supplied to different cells of a polygonal ring connector can be used for fine tuning of optical lenses. Finally, thermal actuators - a switch, tweezers, and a valve - are designed. In terms of overall performance, the actuators are slow but do not exhibit hysteresis: their thermal expansion depends on temperature but not on preceding thermal history. The forces and deflections they achieve compare favorably with piezoelectrics and shape memory alloys.