PSI - Issue 13

Tatyana Tretyakova et al. / Procedia Structural Integrity 13 (2018) 1774–1779 Author name / Structural Integrity Procedia 00 (2018) 000–000

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a b Fig. 4. The crack opening v versus load P (a) and the crack opening v versus time t (b) for specimens with the gauge length: 1-250-H ( 1 ), 1-150-H ( 2 ), 2-100-H ( 3 ) and 2-50-H ( 4 ). As can be seen from the P v  curves (see Fig. 4), the stiffness of the loading system influence on the processes of damage accumulation and the crack propagation during loading. The failure of the longer specimen with 0 250.0 l  mm (curve 1 , see Fig. 4) occurred at the load level of 11.6 P  kN, whereas the deformation of the shorter specimen with 0 50.0 l  mm (curve 4 , see Fig. 4) was followed by the stable crack evolution and the decreasing of load to the zero level. From the point of view of the safety and survivability of structures in emergencies, the possibility of stable crack growth processes are extremely important. The use of the Vic-3D system allows to carry out non-contact measurements of the crack opening in different parts of the specimen and on different gage lengths, as well as to investigate the regularities of inelastic strain development in the stress concentrator region during the propagation of cracks. Figure 5 shows the heterogeneous fields of longitudinal ε yy , transverse ε xx and shear strain ε xy extracted at the load level of 16.6 kN. It should be noted the symmetry of the strain fields relative to the stress concentrator.

Fig. 5. Strain maps: ε yy , ε xx and ε xy at the load level of 16.6 kN for the specimen with 0 50.0 l  mm. Figure 5 displays the results of the DIC-measurement. It is a sequence of four images taken at different load level displaying the evolution of the longitudinal strain fields during a tension test on the specimen with the gauge length 0 50.0 l  mm. On the surface of the specimen, it is possible to observe the inhomogeneity of the plastic deformation due to the crack propagation. The same analysis of the longitudinal strain fields was carried out for specimens with different gauge length. In order to track the crack evolution and to estimate intensity of the failure process during tension tests, the temperature fields were extracted (see Fig. 7) by using of the infrared camera FLIR SC7700M. The higher stiffness of the loading system (the shorter gauge length of the specimen) is the more heated material could be observed in the region of the crack tip. It is interesting to notice here that on the surface of specimens with long gauge length, it is estimated the significant increase of temperature due to the high velocity of the crack propagation along the width. The failure process occurs non-equilibrium.