Investigation of the speckle pattern effect for displacement assessments by DIC

Abstract

Purpose – This study aims to investigate the effect of speckle pattern on displacement measurements using different speckle diameters and coverage ratios. Design/methodology/approach – In order to compare the coverage ratio and speckle diameter during the evaluation of the correlation of digital images (DIC) study, template speckle plates were produced on a computer numerical control (CNC) punch press with 600 punches per minute. After the speckle plates were manufactured, the speckled pattern was randomly painted on a plain white side through the manufactured template plates, and then tensile tests were performed under the same loading conditions for each sample to observe displacement variation via correlation parameters. Findings – During the manufacturing of templates with thin plates, a punch diameter of less than 1.7 mm will cause tool failure; therefore, uniform speckle size can be assessed before operation. A higher coverage ratio resulted in more accurate and reliable results in displacement data. With smaller coverage, the facet size should be increased to achieve favorable results. Research limitations/implications – If thick template plates are selected, speckle painting cannot be done properly; therefore, template thickness shall also be assessed before operation. Practical implications – For randomly distributed DIC templates, increasing coverage beyond 50% does not make sense due to difficulties in the production process in the punch press. Originality/value – Evaluating DIC results via templates manufactured in a punch press with different speckle diameters and coverage ratios is a new topic in literature.

Keywords

• Aluminum alloy
• Tensile test
• Digital image correlation
• Experimental mechanics
• Speckle pattern