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  Journal of Nanoscience Letters 2012, 2: 26
  Research Article
In-situ transmission electron microscopy of fracture in notched thin films
  Sandeep Kumar, Aman Haque§  
Mechanical and Nuclear Engineering; § Materials Research Institute
The Pennsylvania State University, University Park, PA 16802, USA

  It is well established that stress concentration (or strain gradient) is developed ahead of a crack or flaw, whose magnitude depends upon the extent of crack tip plasticity. Ductile materials exhibit strong grain size effects on deformation mechanisms at the nanoscale, yet very little is known about the size effects on stress concentration or fracture. In this paper, we present a unique experimental setup that directly visualizes crack tip deformation using transmission electron microscopy (TEM) while applying and measuring tension in nanoscale freestanding thin films. In-situ TEM experiments on 100 nm thick aluminum and platinum films show remarkably different behavior even though both the materials have FCC crystal structure. We found that aluminum does not show significant dislocation plasticity at the crack tip. Instead, grain rotation is the primary deformation mechanism. For platinum, very large stress concentration at the notch tip (stress concentration factor ~11) was observed, which decreased remarkably as a function of dislocation-based plasticity.
  Size effects on fracture; Stress concentration; Crack tip plasticity; In-situ transmission electron microscopy  

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