The mechanism of strain influence on interpolation induced systematic errors in digital image correlation method

Abstract Digital image correlation methods are widely used in displacement and strain measurements nowadays. Although the influence of strain on measurement accuracy has been extensively discussed, its mechanism is still unknown. In this work, numerical simulations using first-order shape functions are carried out to calculate the displacement of uniform tensile and compressive deformation, and the systematic errors corresponding to different strain values are illustrated and compared. An obvious reduction in the systematic errors can be observed when the strain value is greater than 0.01. The subset size also has an impact on the systematic errors; in particular, systematic errors can be eliminated using a suitable subset size. Furthermore, the mechanism of the influence of strain and subset size on systematic errors is revealed: the sub-pixel interpolation errors in deformed subsets bring forth systematic errors, and the existence of strain contributes to the sizes of the induced systematic errors. An analytical formula describing the relationship between systematic errors and strain/subset size is deduced and verified. This work can help researchers predict systematic errors for certain strains and subset sizes, while furthering our understanding of the role of strain in correlation calculations.