Normally the strain field is indirectly determined by differentiating the displacement fields. This indirect method always suffers from noise, and the shear strain accuracy is poor due to the rigid body rotation effect. In this paper, a direct strain measurement method based on affine transform matrix decomposition is introduced. A new method for strain matrix inversion without determining the rotation is proposed. This can be used for both local and global 2D/3D strain determination. A uniaxial tensile test with grid measurement technique is carried out to validate this method.

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