Issue34

K. Nowak, Frattura ed Integrità Strutturale, 34 (2015) 34 (2015) 507-514; DOI: 10.3221/IGF-ESIS.34.56 510 (a) (b) (c) (d) Figure 2 : Initial uncracked structure (a) , structure with edges cracks (b) , with central cracks (c) and with both cracks types (d) . Dimensions are in millimetres. Due to symmetry the calculations are performed in the greyish quadrant of the plate. A NALYSIS OF A PLATE WITH SINGLE INITIAL CRACK Edge crack or the structure with edge crack (Fig. 2b) the time of first failure occurrence is found to be t 1e =99.1h. Then the crack develops due to damage growth and finally spans the width of the plate in time t 2e =795h. As the damage is driven by the maximum principal stress (  = 1.0) the path of the crack is straight. The rate of the crack growth at the beginning is equal to 1.84E-5m/h and it is increasing as the crack becomes longer. When the crack length achieves its critical value in creep condition the rate of the growth becomes relatively high and is equal to 1.22E-2m/h (marked in Fig. 3 by a red point). The critical length of the crack at this instant is close to 68mm. 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0 200 400 600 800 t [h] locus of the crack tip [m] Figure 3 : Development in time of the edge crack. Small variations of the curve shown in Fig. 3 is because the crack growth rate is subjected to small fluctuations as the constitutive model consists of two parts, elastic and creep ones. The elastic stress is very high at crack tip and due to relaxation this high value is decreasing in time. Simultaneously the damage is developing, the crack tip changes its position and new elastic stress is raised. F