Nanowires have become an increasingly prevalent nanomaterials in composites and devices, as both surface coatings and in mechanically coupled sensing applications.  Despite the importance of failure behavior and mechanisms in load bearing applications, little investigation has been done regarding the mechanical behavior of these micron sized structures.  Though in-situ microcompression experiments on highly aligned dense bundles of single crystalline zinc oxide (ZnO) nanowires we investigate these types of structures to build a model for better understanding structural failure.  The ZnO nanowires are hydrothermally growth in bundle structures with a constant nanowire diameter of approximately 300nm and a range of 10-130 nanowires per bundle.  Experiments show two regimes of failure in the nanowire bundles: localized non-catastrophic events and global structural failure.  No size dependence is observed in either regime and failure stress ranges from 0.3-1.3GPa and 0.83-2.20GPa respectively.  Localized failure corresponds to interfacial splitting between nanowires and can be modeled using a mode I double cantilever beam tests.  Analysis of this mechanism provides insight to the flaw size and failure initiation in the structures.  Ultimate global failure can be modeled by coupling the accumulation of local failure from interfacial splitting to specific failure parameters of the nanowire material.  Utilizing Weibull statistics and experimental results, we demonstrate the validity of this technique for analyzing flaw distribution and predicting the expected failure stress range of the bundle structures.  The technique shows the sensitivity of failure behavior to degree of alignment, flaw size, interfacial interactions of constituents, and structural surface effects.  Through analysis of behavior in this specific system, we develop insight to broader fundamental mechanisms for local failure and statistical techniques for assessing and predicting failure behavior of highly aligned structures.

Failure Behavior and Mechanisms in Dense Highly Aligned Brittle Nanowire Structures

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