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. 2018 Sep 29:5:1166-1177.
doi: 10.1016/j.mex.2018.09.012. eCollection 2018.

Fracture toughness testing using photogrammetry and digital image correlation

Wen Hao Kan  1   2 , Carlos Albino  3 , Daniel Dias-da-Costa  4 , Kevin Dolman  5 , Timothy Lucey  5 , Xinhu Tang  5 , Julie Cairney  1   2 , Gwénaëlle Proust  4
Affiliations

Fracture toughness testing using photogrammetry and digital image correlation

Wen Hao Kan et al. MethodsX. .

Abstract

Digital image correlation (DIC) is an optical technique commonly used for measuring displacement fields by tracking artificially applied random speckle patterns, which can sometimes be a problem for tracking small-scale displacements. DIC is particularly useful for tracking the crack mouth opening displacement (CMOD) of a notched metallic specimen subjected to three-point bending for fracture toughness determination because the edges of the notch provide the required textural features for DIC without the need for speckle patterns. This simplifies the set-up process as the specimen and stage geometries do not need to account for the placement of a strain gauge. To enhance the accuracy of DIC, this study then successfully downscaled a photogrammetry technique commonly used to track crack propagation in large scale concrete tests so that the pixel coordinates of the captured images can be automatically related to their real-world coordinates, allowing for small scale displacements to be accurately tracked.

Keywords: Digital image correlation (DIC); Digital image correlation with photogrammetry; Fracture toughness; High chromium white cast iron; Metal matrix composite; Photogrammetry.

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Figures

None
Graphical abstract
Fig. 1
Fig. 1
Typical three-point bending set-up: (a) schematic of the set-up, (b) actual specimen with attached photogrammetric targets, (c) schematic of the specimens showing dimensions.
Fig. 2
Fig. 2
Representation of the ROI: (a) initial reference image before deformation; (b) stage monitored after significant displacements occurred.
Fig. 3
Fig. 3
(a) CMOD measured during the test, with an onset of plasticity at approximately 6.9 kN and tested up to a load of 10.2 kN; and validation using SEM (b) before and (c) after the test.
Fig. 4
Fig. 4
Typical Load vs. CMOD data obtained using the proposed image processing technique. The extrapolation of results in between points is shown by the black line. 95% secant slope shown by the red dashed line. PQ and Pmax values are marked on the plot.
See this image and copyright information in PMC

References

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