Issue 46

A. Kostina et alii, Frattura ed Integrità Strutturale, 46 (2018) 332-342; DOI: 10.3221/IGF-ESIS.46.30 339 (a) (b) Figure 6 : Temperature rise at the crack obtained by isotropic damping model and Maxwell’s model: (a)  =10 -4 , v  =5.5*10 -10 s (solid line – isotropic damping model, dashed line – visco-elastic Maxwell’s model); (b)  =10 -5 , v  =5.5*10 -11 s (solid green line – damping model, the magnitude of the surface load is 100 MPa; solid blue line – damping model, the magnitude of the surface load is 10 MPa; cyan dotted line – Maxwell’s model, the magnitude of the surface load is 100MPa; red dotted line – Maxwell’s model, the magnitude of the surface load is 10 MPa). The more pronounced dependence the obtained results have upon the applied loading frequency. Fig. 7 presents temperature rise at the crack tip for the four values of the loading frequency: 10000 Hz, 20000 Hz, 30000Hz and 50000 Hz. It can be seen that the increase in the loading frequency gives approximately twofold increase in the maximum value of the temperature rise at the crack tip. Therefore, the increase in the value of the loading frequency can help to improve the visibility of the crack. Figure 7 : Temperature rise at the crack tip under various frequency loading (solid line – 50000 Hz, dotted line – 30000 Hz, dashed line – 20000 Hz, dash-dot line – 10000 Hz). The way in which the load is applied to the specimen is also affects the visibility of the crack. Figs. 8 and 9 show the distribution of the temperature rise in case when the applied load is directed parallel to the crack plane. In this case, the crack is rotated on 90 degrees with regard to the case presented in Fig. 2. The surface load is applied to the opposite end of the specimen. This kind of loading leads to the stationary wave, whose peak amplitude does not move in space. The crack tip location coincides with nodes of the wave. On the initial stage of the loading process, the crack tip is visible (fig. 8(a), 9(a)). Further loading leads to the heating of the whole specimen (fig. 8(b), 9(b)) and blurring of the temperature localization at the crack tip. The maximum temperature values are in the antinodes of the wave under such loading. The obtained results also shows that Maxwell’s model gives more pronounced crack tip compared to the isotropic damping model.