Application of the mean intensity of the second derivative in evaluating the speckle patterns in digital image correlation

• The effects of speckle pattern quality on DIC measurement accuracy were investigated.
• A new global parameter was proposed to evaluate the quality of the speckle patterns.
• High quality speckle patterns should have a large MIG and a small MIOSD.

In this work, the mean intensity of the second derivative of speckle pattern was used to quantify the quality of the speckle patterns for digital image correlation. Numerical experimental studies were performed to justify the correctness and effectiveness of this new global parameter. The results indicate that the measured displacement error was related to the mean intensity of the second derivative of the speckle patterns when they had equal mean intensity gradients. The results also indicate that the measurement accuracy was affected by both the mean intensity gradient and the mean intensity of the second derivative. Therefore, high quality speckle patterns should have a large mean intensity gradient and a small mean intensity of the second derivative.