Analysis of the Deformation Behavior of Materials During Indentation Using Digital Image Processing Methods

The combination of indentation with high-quality imaging of a tested sample is applied to obtain new data on deformation processes in materials through the implementation of a digital processing method for a series of sequential images. This work involves the analysis of residual indentations that occur in the material after the indentation of a Vickers diamond pyramid. The study focuses on the deformation behavior of a steel sample of grade 40Kh2N2MA with graphite inclusions and an aluminum alloy modified with fullerene. Testing is conducted using a NanoScan-HV device and observations are made in the dark-field mode, chosen to enhance image contrast. The testing scheme corresponds to State Standard GOST R ISO 6507–1–2007 and the obtained images of the indentations are analyzed using software implemented in Python. Displacement field maps are constructed, and the dependencies of the residual displacement of points on the indented surface relative to the initial image are calculated. Image-processing recommendations are put forward that will allow for the implemented algorithm to be applied to the study of materials that are heterogeneous in structure and appearance. In the first step of the algorithm, a Hanning window is applied to eliminate edge effects during the subsequent two-dimensional Fourier transform. Then, the direct Fourier transform is computed for the image before and after indentation. Following this, the spatial shifts in the microregion of the image are determined using mutual spectral analysis. The algorithm employs the fast Fourier transform to accelerate calculations. After determining the shift value with maximum correlation in its vicinity, the coordinates of the weighted centroid are calculated based on correlation values for nearby displacements. This allows for subpixel accuracy. The resulting maps and dependencies of residual deformations with respect to distance are informative for analyzing the dominant mechanisms of the influence of local mechanical pressure on the plastic deformation of the tested material.