Digital image correlation is widely used in non-contact displacement/strain measurements for numerous engineering applications. Under rigid body rotation or shear deformation, however, the calculated surface strain of specimens is unreliable when camera pixels are characterized by non-square geometry, that is, the width-to-height ratio of pixels is not 1. This study analyzes the computational errors introduced by cameras, and proposes a modified least-squares method that eliminates such errors when the strain field is calculated. Experimental results confirm that the algorithm validly and effectively computes shear strain.
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