Issue 46

V. E. Wildemann et alii, Frattura ed Integrità Strutturale, 46 (2018) 295-305; DOI: 10.3221/IGF-ESIS.46.27 300 (a) (b) Figure 5 : The ' P u  ’ and ‘ M   ’ curves obtained in tension-torsion test of specimen with embedded defects ( 0.028 k  ): (a) type 1, (b) type 2. It is of interest to analyze the evolution of inhomogeneous longitudinal deformation fields on the surface of the studied specimens under loading. Fig. 6 shows the time dependence of the axial load for a specimen with a defect of 20×20 mm 2 (Fig. 7). For the points 0 4 t t  the evolution of the longitudinal deformation fields ( ε yy ) is presented in Fig. 7. The axis Oy is directed along the loading axis of the specimen. It is worth mentioning that there is an insignificant increase of thickness in the region of the defect, which is associated with the characteristic property of the “delamination type” defect development on the specimen’s surface. This thickening is recorded by the video system and illustrated in Fig. 7 as an image of the distribution of the coordinate z (the axis Oz is perpendicular to the plane of the specimen). Points 1 3 t t   correspond to the specimen’s reloading instances at 10 P  kN. In the region of the defect, the presence of inhomogeneity of the longitudinal deformation fields was observed, while in this zone the level of longitudinal deformation is below the average value over the whole specimen. The degree of inhomogeneity increases in the process of loading. To illustrate the observed defect, the dependences of longitudinal deformations were built along the specimen (along the axis Oy ) for points 0 4 t t  (Fig.8). The level of the axial load ( P ) in the specified points is equal to 10, 20, 30, 40 and 50 kN respectively. Vertical dashed lines show the boundaries of the defect. Fig. 9 shows similar dependences of longitudinal deformations, built for points 0 t and 1 3 t t   . It should be noted that the configuration of the curves ε yy y  at the instants of the specimen’s reloading at the level of axial load 10 P  kN does not change, which indicates that the internal defect does not develop during the test.