Hierarchical Materials: Modeling, Manufacturing, and Testing of Lightweight Metals with Zero and Tunable Thermal Expansion: FY17 Engineering Research Technical Investment Program
MIT Lincoln Laboratory Lexington United States
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A particularly challenging yet common problem at MIT Lincoln Laboratory is designing prototypes to function under repeated variations of temperature. Thermal expansion of components causes separation and alignment errors in optical systems, and stresses due to mismatches of thermal expansion at material interfaces cause fatigue and failure of components and structures. In addition to managing thermal expansion, minimizing system weight and maintaining short production cycles are critical requirements. However, presently available materials with low thermal expansion either are heavy or are expensive with long fabrication lead times. Furthermore, existing materials have essentially fixed thermal expansions and provide only limited freedom to tune the response to the requirements of an application. These materials are solid materials with properties determined primarily by their elemental composition and microstructure. Here, we take a different approach and engineer materials by specifying underlying structure at one or more hierarchical levels to create materials with zero and tunable thermal expansion and high specific stiffness. Analytical and numerical models are used to design lattice-based cellular materials composed of two constituent materials with dissimilar thermal expansions. The lattice geometry and layout of constituent materials can be chosen to achieve zero or otherwise specified thermal expansion while maximizing specific stiffness, subject also to the constraints of automated manufacturing. Samples were manufactured with 3D printing and computer-controlled machining, and thermal expansion was measured with a novel optical method. The experimental results show effective thermal expansions ranging from -14.0 X 10 exp -6 K exp -1 to 17.1 X 10 exp -6 K exp -1, demonstrating that we have developed the first metals with zero and tunable thermal expansion to our knowledge that can be manufactured with automated methods at useful scales.
- Metallurgy and Metallography
- Radio Communications