Optical method for monitoring deformations when processing cylindrical workpieces

The article discusses a method for monitoring deformations to study the features of their localization along the length of axisymmetric long samples under tension. This is relevant for the process of thermal power processing, which consists in using a given force and temperature influence on the workpiece to ensure its straightness with equalization of residual technological stresses. Since the process takes place in the plastic loading zone and the workpiece is pulled out during transverse deformation along sections, in order to form a given dimensional accuracy and uniformly distribute the allowance for subsequent machining, it is necessary to know the patterns of changes in deformations taking into account the loading parameters. To record the distribution of displacement fields during loading, an optical method is used to control deformation on the surface based on the digital image correlation method. Based on the analysis of a series of sequential digital images of a deformable sample, previously prepared for shooting by applying speckle on it in the form of randomly distributed black dots of paint on a white matte surface, using a local gradient method of digital image correlation, a field of displacements and deformations is recorded for given areas. The results of a study of the influence of the type of speckle on the accuracy of determining displacements and deformations are presented. The technique of obtaining and processing digital images is considered, including conversion to a halftone image, distortion correction and image sharpening using filters. The results of studies on determining deformations using the optimal parameters of the size of the correlation window, the step of its displacement, the sensitivity threshold for the illumination gradient, and the parameter of the Gaussian filter used are presented. The use of the proposed control method provides the ability to monitor with the required accuracy deformations along the length of long cylindrical workpieces, which facilitates the selection of technological modes of thermal power processing in terms of the magnitude and rate of deformation in order to ensure the most uniform distribution of plastic deformation.