2013 | OriginalPaper | Chapter
Extended DIC to Measure Stress Intensity Factors from AFM-images
Authors : S. Roux, M. Ciccotti, F. Hild
Published in: Application of Imaging Techniques to Mechanics of Materials and Structures, Volume 4
Publisher: Springer New York
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Subcritical crack propagation in amorphous silica glass can be imaged during propagation with an AFM at different stages of propagation. Digital Image Correlation constitutes an attractive technique to measure the displacement fields relating different topographic images, and from it to estimate quantitatively the stress intensity factor governing the crack velocity. However, the emergence of the crack on the free surface, which is imaged, induces a significant out of plane motion whose magnitude is comparable to the surface roughness. This difficulty calls for an extension of the usual “brightness conservation” allowing for an evolution of the image texture, i.e. surface topography. The high level of AFM-image noise is tackled through integrated DIC, namely, few well chosen kinematic fields are selected to decompose the searched displacement field. The latter are considered because of their mechanical relevance to the problem at play (e.g., rigid body motion, plane stress mode I displacement field, out-of plane singular field) or to compensate for AFM artifacts. The resulting novel DIC algorithm provides directly an evaluation of the stress intensity factor,
KI
, without any further post-processing; 10% (resp. 15%) uncertainty on
KI
is achieved based on 1 × 1 μm
2
(resp. 200 × 200 nm2) images.