Brittle materials such as silicon fail via the crack nucleation and propagation, which is characterized by the singular stress field formed near the crack tip according to Griffith or fracture mechanics theory. The applicability of these continuum-based theories is, however, uncertain and questionable in a nanoscale system due to its extremely small singular stress field of only a few nanometers. Here, we directly characterize the mechanical behavior of a nanocrack via the development of in situ nanomechanical testing using a transmission electron microscope and demonstrate that Griffith or fracture mechanics theory can be applied to even 4 nm stress singularity despite their continuum-based concept. We show that the fracture toughness in silicon nanocomponents is 0.95 ± 0.07 MPa√m and is independent of the dimension of materials and therefore inherent. Quantum mechanics/atomistic modeling explains and provides insight into these experimental results. This work therefore provides a fundamental understanding of fracture criterion and fracture properties in brittle nanomaterials.
Owing to a finite and single-atom-thick two-dimensional structure, graphene nanostructures such as nanoribbons possess outstanding physical properties and unique size-dependent characteristics due to nanoscale defects, especially for mechanical properties. Graphene...
Crystal
defects often lead to an intriguing variety of catastrophic
failures of materials and determine the mechanical properties. Here
we discover that a dislocation, which was believed to be a source
of plasticity, leads to brittle fracture in SrTiO3. The
fracture mechanism, i.e., bond breaking at the dislocation
core triggers crack initiation and subsequent fracture, is elucidated
from an atomic view by hybrid quantum and molecular simulations and in situ nanomechanical experiments. The fracture strength
of the dislocation-included SrTiO3 was theoretically evaluated
to be 8.8–10.7 GPa, which was eminently lower than that of
the pristine one (21.7 GPa). The experimental results agree well with
the simulated ones. Moreover, the fracture toughness of the ultrasmall
crack initiating from the dislocation is quantitatively evaluated.
This study reveals not only the role of dislocations in brittle fracture
but also provides an in-depth understanding of the fracture mechanism
of dislocations at the atomic scale.
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