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Open AccessFeature PaperArticle

Comparing In Situ DIC Results from an Etched Surface with a Gold Speckled Surface

1,2,*,†, 2,3,†, 2,3,† and 1,2,†
1
Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway
2
Centre for Advanced Structural Analysis (CASA), NTNU, NO-7491 Trondheim, Norway
3
Structural Impact Laboratory (SIMLab), Department of Structural Engineering, NTNU, NO-7491 Trondheim, Norway
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Metals 2019, 9(8), 820; https://doi.org/10.3390/met9080820
Received: 22 June 2019 / Revised: 16 July 2019 / Accepted: 22 July 2019 / Published: 25 July 2019
(This article belongs to the Special Issue Quasi-Static and Dynamic Testing of Metallic Materials)
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Abstract

A ferrite-pearlite two-phase steel was investigated using in situ scanning electron microscope (SEM) tensile testing combined with digital image correlation (DIC). Two different speckled patterns were used and compared. The first pattern was achieved by etching a polished surface in order to reveal the microstructural features. Second, a gold speckled pattern was obtained. Here, a continuous layer of gold was applied to a polished surface. This continuous layer was remodeled into gold nanoparticles by keeping the specimen at 180 °C for 96 h with an Ar/Styrene mixture flowing across the specimen surface. The result is randomly distributed gold nanoparticles on the surface. These particles and the etched microstructure were then used by the DIC software to correlate an image series to obtain the local strain field of the material. The differences between the two techniques are numerous. Considering the etched surface, most microstructural features were grain boundaries and pearlite lamellas. As a consequence, large areas within grains did not provide sufficient contrast for DIC, thus restricting maximum resolution. However, the technique is fast and does not expose the material to any elevated temperatures. In contrast, the gold remodeling method provides a finely dispersed gold speckle pattern on the surface, giving excellent contrast across the recorded area. DIC with gold particles achieved a spatial resolution of 0.096 µm, compared to 2.24 µm in the DIC for the etched specimen. As a result, DIC with gold speckles can resolve slip lines. Conversely, DIC with etched microstructure resolves local strains on grain level. However, it is less cumbersome and faster to perform the test on the etched specimen. View Full-Text
Keywords: digital image correlation; in situ testing; scanning electron microscopy; strain localization digital image correlation; in situ testing; scanning electron microscopy; strain localization
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Paulsen, C.O.; Fagerholt, E.; Børvik, T.; Westermann, I. Comparing In Situ DIC Results from an Etched Surface with a Gold Speckled Surface. Metals 2019, 9, 820.

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