Special considerations in reflective coherent gradient sensing method for measuring large deformations

In this study, reflective coherent gradient sensing (CGS) method is introduced to measure large deformations of Ni-Cr alloy in instrumented indentation. The effects of grating distance, collimation property of incident beam, camera lens focal length, screen and specimen location are analyzed. The presence or absence of screen and the camera lens focal length are found out to be the most important factors when measuring large deformations with CGS method. Moreover, we develop a method to obtain the 'true' interferograms by Fourier and inverse Fourier transformation algorithms. The measuring scale of reflective CGS method for large deformation is obtained. A criterion is developed to distinguish the boundaries between small and large deformations in measuring inhomogeneous deformations with reflective CGS method.