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 degrees 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,similar to 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 delta) at room temperature as high as 0.5. This study attests to the ability of BNNT macroassembly to bear mechanical stresses up to 750 degrees 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.