Measurement of nonhomogeneous deformations fields by digital image correlation method with multiscale sensitivity

ABSTRACT. A review of progress in numerical synthesis and study of strain sensor patterns, which can be used for realization of the digital image correlation (DIC) method and its applications in engineering practice is made. This method is becoming more popular in the research and monitoring of deformation fields of relatively large parts and structures. In these cases it is necessary to obtain quantitative information not only about the total deformation fields of objects, but for local deformations developing in the vicinity of stress concentrators at observed surfaces, or generally speaking - for the full nonhomogeneous deformations fields. This paper is devoted to solution of problems related to monitoring a large area of the object surface with subsequent increasing the image scale and concentration the observation only to the place where largest deformation has been localized. The strain sensor pattern has to be generated on such a way which will ensure that a change of the image scale will not decrease DIC method sensitivity and spatial resolution. An algorithm for numerical synthesizing of specialized strain sensor patterns is proposed. Theoretical considerations regarding requirements to these patterns for DIC applications are presented and algorithms for their computer generation, as well as for post processing of their images recorded with different zoom are reported. Quality evaluation of this type of patterns is performed and it is compared with the quality of similar images used by other authors. The possibility through DIC and the proposed strain sensor patterns to be measured fields of displacements and deformations at different scales while maintaining appropriate sensitivity and spatial resolution of the method, is shown by numerical experiments. Results from a physical experiment are reported also, which demonstrate the applicability of the introduced approach for measurement of a full nonhomogeneous deformation field through “switching over” the magnification (zooming) of recorded images and localizing the observation only at relatively small zone where biggest deformation is arisen during the experiment. KEYWORDS: Digital image correlation, multiscale, non-homogeneous deformation