High-Temperature Mechanics of Boron Nitride Nanotube “Buckypaper” for Engineering Advanced Structural Materials

Boron nitride nanotube (BNNT) is an attractive load-bearing nanomaterial with excellent mechanical properties and high-temperature stability. In this study, the mechanics of BNNT buckypaper assembly is examined at elevated temperatures (up to 750 °C). In situ mechanical investigations are performed inside the electron microscope for real-time visualization of deformation. The deformation characteristics are examined at multiple hierarchical levels to understand the role of defects in a single nanotube, stress-transfer between entangled nanotubes, and interactions between multiple nanotube layers of the buckypaper. The ultralightweight buckypaper is flexible and damage-tolerant and withstands repeated loading/unloading/reloading indentation cycles with an elastic modulus ∼0.8–1.2 GPa. Digital image correlation analysis of the real-time videos indicates excellent strain re-distribution in the buckypaper, which prevents localized stress-concentration. In situ high-speed camera imaging during tensile deformation reveals crack-deflection and crack-bridging due to nanotube entanglements, providing failure-resistance. The buckypaper has energy-dissipation ability, with loss tangent (tan δ) at room temperature as high as 0.5. This study attests to the ability of BNNT macroassembly to bear mechanical stresses up to 750 °C. The application of this macroassembly for developing a polymer-based nanocomposite with superior stiffness (1170% improvement) is also demonstrated. The findings in this work can be applied for engineering BNNT-based advanced structural materials.