Development of designing lightweight composites and structures for tailorable thermal expansion

Abstract

Thermal expansion coefficient is an important parameter of thermal physical properties. Materials with zero thermal expansion (ZTE) are urgently needed in engineering applications, particularly in aerospace, precision instruments, and civil engineering, where the control of thermally induced expansion and stress over a wide range of temperatures is of significance. On the other hand, thermal expansion compensation requires materials to possess negative thermal expansion (NTE) and even a desirable positive thermal expansion (PTE). For example, thermal expansion modulation can be achieved via composites with an appropriate ratio of NTE inclusions and PTE substrates. In general, engineering applications have a serious need for materials and structures with tailorable CTEs. Hence, development of material with tailorable thermal expansion is of important scientific significance and engineering applications. At present, the available range of CTE in engineering materials is quite narrow. To obtain wide range of CTE, most of current researches are mainly concentrated on bulk materials and composites. Specifically, few bulk materials with low and negative CTEs have been reported. FeNi-based Invar alloysexhibit low CTEs because of the magneto-volume effect which, however, only exists under the Curie temperature (about 100°C). A family of ceramics with isotropic NTE and metal oxides with anisotropic NTEs, has been widely studied. Unfortunately, the inherent brittleness and low fracture toughness of the NTE ceramics restrict their usage in load-bearing applications. Fiber-reinforced composites are capable of providing tailorable CTEs because some fibers, such as carbon and graphite fibers, possess negative axial CTEs. However, largely different CTEs between the fiber and the matrix always result in matrix cracking under large temperature variation. Besides, through topology optimization of the three-phase composites, ZTE and the maximum uniaxial/biaxial stiffness characteristics can be obtained. However, the optimized geometries are still too complex for practical manufacture and engineering applications. It is important to integrate tailorable CTE with lightweight and robust mechanical properties for the materials. Lightweight composites attract intensive studies by virtue of their low density, excellent mechanical properties as well as tailorable thermal expansion coefficient. This paper firstly summarizes the significant engineering applications of thermal expansion controlling as well as the bulk materials with low and negative thermal expansion. Moreover, research achievements of the laminate, particle reinforced and topologically optimal composites with tailorable thermal expansion are detailly introduced. Finally, we present the latest research progress including geometry design methods, mechanisms, fabrication process and experimental characterization of tailorable thermal expansion for lightweight lattice composites. The design of lattice materials which are assembled through dual-material members, and honeycomb-like hybrid lattices which are composed of inner triangle and outside honeycomb initiates the macro scale lightweight lattice composites for tailorable CTE. However, the lattice composites with bending-dominated members display less stiffness compared with stretch-dominated lattices. Moreover, the complicated geometrical connections of the members lead to manufacture complexity. Triangle lattice composite exhibits tailorable CTE and are used as the basic unit to construct other lattice configurations such as the near zero thermal expansion lattice structures. Thus, numerous studies find the planar lattices and structures design based on this unit. With the development of advanced manufacturing technology, the study of the lightweight lattice composites will be promoted more deeply.