Issue 46

V. E. Wildemann et alii, Frattura ed Integrità Strutturale, 46 (2018) 295-305; DOI: 10.3221/IGF-ESIS.46.27 297 At the initial stage specimen blades without defects with proportional tension with torsion were tested with the control of position and torsion angle at different ratios of the given displacement and the torsion angle ( k u   ). The testing parameters are given in Tab. 2. The specimens with defects were loaded at the selected ratio of the predetermined displacement to the torsion angle ( 0.028 k  ) until ultimate fracture. (a) (b) Figure 1 : (a) Sketch and (b) photo of specimen with embedded defect ‘delamination’. № Torsion rate, °/min Tension rate, mm/min k u   1 0 60 0 2 5.0 60 0.083 3 5.0 90 0.056 4 2.5 90 0.028 Table 2 : Test parameters for proportional tension with torsion. During loading, the displacement and deformation fields were registered on one of the surfaces of the specimens by using the contactless three-dimensional digital optical system Vic-3D. The software of the vision-based system is based on the method of digital images correlation [25]. The shooting is realized by a set of high resolution cameras (Prosilica, 16 Mp) with a recording frequency of 3.5 Hz. Post-processing of the obtained images was carried out using the criterion of the normalized sum of squared differences (NSSD); to calculating the fields of longitudinal ( ε yy ), transverse ( ε xx ) and shear deformations ( ε xy ), the finite strain tensor in the Lagrange representation is used. Whereas the axis Oy is directed along the specimen (along the axis of tension), the axis Ox is perpendicular to the axis of loading in the specimen’s plane. To identify the location and geometric parameters of technological defects of the “delamination type”, the method of active infrared thermography was used, while the temperature fields were registered with the infrared thermal imaging system Flir SC7700M. The thermal imager is equipped with a detector of the “cadmium-mercury-tellurium” type, has a resolution of 640 × 512 pixels, a recording rate of 115 Hz (at full resolution) and a sensitivity of <0.025 °C.