Investigation of the speckle pattern effect for displacement assessments by DIC

Abstract

PurposeThis study aims to investigate the effect of speckle pattern on displacement measurements using different speckle diameters and coverage ratios.Design/methodology/approachIn 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.FindingsDuring 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/implicationsIf thick template plates are selected, speckle painting cannot be done properly; therefore, template thickness shall also be assessed before operation.Practical implicationsFor randomly distributed DIC templates, increasing coverage beyond 50% does not make sense due to difficulties in the production process in the punch press.Originality/valueEvaluating DIC results via templates manufactured in a punch press with different speckle diameters and coverage ratios is a new topic in literature.