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Proceedings 2018, 2(8), 451; https://doi.org/10.3390/ICEM18-05311

Using 3D Digital Image Correlation (3D-DIC) to Measure CTOD in a Semi-Elliptical Surface Crack

Department of Electrical Energy, Metals, Mechanical Construction and Systems (EEMMeCS), Soete Laboratory, Ghent University, 9052 Zwijnaarde, Belgium
Presented at the 18th International Conference on Experimental Mechanics (ICEM18), Brussels, Belgium, 1–5 July 2018.
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Published: 8 June 2018
PDF [3032 KB, uploaded 22 June 2018]

Abstract

The subsurface nature of Crack Tip Opening Displacement (CTOD) makes its direct measurement very difficult, if not impossible. During fracture toughness testing, CTOD is commonly calculated by applying a plastic hinge model using externally applied clip gauges. However, clip gauge CTOD calculations merely provide information relating to the center of the defect (which is typically the most critical point, but not always). For the case of a finite-length surface defect, CTOD will be variable over the defect front. Exact knowledge of CTOD over the entire front is useful for detailed calculations, such as crack profile evolution due to ductile tearing or calculations involving interacting defects. To experimentally measure the CTOD at locations other than the center of the crack, the authors propose a technique based on full field three-dimensional profile measurement of the notched surface by means of stereoscopic Digital Image Correlation (3D-DIC). The method is based on the plastic hinge model assuming that the crack flanks rotate in a rigid manner around a plastic hinge point in the un-cracked ligament. Having measured full-field out-of-plane displacement at the surface of the specimen around the crack using the 3D-DIC method, CTOD can be inferred over the entire crack front. Results show that, due to the acceptable agreement between the DIC based calculation and CTOD measured from cast replicas, the proposed technique has a sufficient accuracy to measure CTOD on the entire crack front in plastically deforming specimens.
Keywords: CTOD; Digital Image Correlation; replica; ductile tearing; crack front; semi-elliptical CTOD; Digital Image Correlation; replica; ductile tearing; crack front; semi-elliptical
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Samadian, K.; Hertelé, S.; Waele, W.D. Using 3D Digital Image Correlation (3D-DIC) to Measure CTOD in a Semi-Elliptical Surface Crack. Proceedings 2018, 2, 451.

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