Fracture toughness testing using photogrammetry and digital image correlation

Area of Science:

• Materials Science
• Mechanical Engineering
• Optical Measurement Techniques

Background:

• Digital Image Correlation (DIC) is a key optical technique for measuring displacement fields.
• Traditional DIC relies on speckle patterns, which can limit accuracy for small-scale displacements.
• Notched metallic specimens offer natural features for DIC, simplifying setup for fracture toughness tests.

Purpose of the Study:

• To improve the accuracy of DIC for measuring small-scale displacements.
• To adapt photogrammetry for precise crack mouth opening displacement (CMOD) tracking in metallic fracture tests.
• To eliminate the need for artificial speckle patterns in DIC analyses.

Main Methods:

• Downscaling a photogrammetry technique from large-scale concrete crack tracking.
• Applying the technique to notched metallic specimens under three-point bending.
• Automatically relating pixel coordinates to real-world coordinates for accurate displacement measurement.

Main Results:

• Successfully enabled accurate tracking of small-scale displacements using DIC.
• Demonstrated the efficacy of the downscaled photogrammetry technique for CMOD measurement.
• Validated the method's ability to leverage natural specimen features, negating the need for speckle patterns.

Conclusions:

• The adapted photogrammetry technique significantly enhances DIC accuracy for small displacements.
• This method simplifies fracture toughness testing by utilizing inherent specimen geometry.
• The study presents a robust approach for precise CMOD measurement in metallic materials.