13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- 3.2. Meso I level. Analysis of AE registration data Dependences of AE count rate versus loading time dNАE/dt for specimens are shown in fig. 3. This parameter was chosen for the analysis as being most "sensitive" to change of a leading scale level of deformation in a specimen under loading. The point graphs of AE count rate were smoothed by average curves. For both types of specimens it is visible, that generation of AE pulses begins practically from the beginning of loading. However appreciable increment of the AE count rate starts at time related to transition of key role of deformation to the meso-scale level. Fig. 3. Combined dσ/dt - γdif - dNAE/dt graphs: a) specimen with central hole: ∅7 mm; b) specimen with edge crack: 14,5 mm. 3.3. Meso II level. Shear strain intensity The analysis of strain evolution at the meso II level was made by 2 methods of image processing: integral and differential (detailed description of the technique is given in paper [8]). In the first case displacement vectors were mapped by comparison of a first (initial) image with each current ones, while at the differential method of calculation a current and a subsequent images of a deformed specimen surface were compared. Dependences of the shear strain intensity calculated by the differential method of the image processing which is more sensitive to local strain changes, for both types of specimens are presented in fig. 3. These dependences are sectionally-linear approximated. 4. Conclusions Combination of DIC and AE data used in the research allows us to examine stage patterns for deformation development at various scale levels. In our previous investigations aluminum specimens were tested [9]. For aluminum specimens at the initial stages of loading the AE method seems to be the most sensitive to deformation processes. At greater degrees of deformation the method of digital images correlation (DIC) more precisely characterizes the change of the key role from meso- to macroscopic scale of the deformation development. For CRFC specimens AE method have high sensitivity and ability to describe processes inside material, strain gauging characterizes response of specimen on applied stress and allows to identify transition between stages, DIC method can be used to visualize deformation processes with their numerical estimation. The results are offered to be applied for the aims of non-destructive testing of structural materials being based on revealing characteristic stages of strain development and particularly prefracture stage.
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