Issue 53

E. M. Strungar et alii, Frattura ed Integrità Strutturale, 53 (2020) 406-416; DOI: 10.3221/IGF-ESIS.53.31 408 distribution for the possibility of conclusive identification of local areas from the image. At smaller parameter size  , the unaffordable correlation ratio values are observed. Based on the study conducted it is observed that the selection of parameters should be performed in consideration of the size of structural non-homogeneity of the material; in view of this fact, the scale level of deformation registration is selected. To assess the structural specificity of the material, to study the processes of origin and development of defect structures and damage, the analysis of behavior in the stress concentration zones it is necessary to establish the step value consistent with the structural non-homogeneity size [21]. Figure 1: The effect of subarea size on the results of calculation of correlation ratio; non-homogeneous longitudinal strain fields at a fixed size of subarea and various step values. Due to the fact that the video-system precision is not a fixed value but depends on various mathematical parameters, the authors conducted a study to confirm the precision of the measurements obtained using a three-dimensional optical system, a series of tests for uniaxial stretching of a fiberglass flat sample was carried out using amounted extensometer Instron 2620-601 and additional Vic-3D software module of “virtual extensometer” (Fig. 2). The characteristics of the extensometer Instron 2620-601 are as follows: the maximal possible deviation from the measured value is 0.15%. The measuring base of the mounted extensometer is 50 mm. Figure 2: Longitudinal strain-time diagram. According to the test results, it was concluded that the use of a digital optical system makes it possible to determine the deformation values on a fixed basis, with the accuracy consistent with the data of the mounted longitudinal strain gauge