Issue 36

A. Sedmak et alii, Frattura ed Integrità Strutturale, 36 (2016) 63-68; DOI: 10.3221/IGF-ESIS.36.07 64 23% and 27%), while two other had significantly lower values of elongation (A 5 = 8% and 9%). Obtained values of fracture mechanics parameters (critical stress intensity factor - K Ic , critical fatigue crack length - a c , fatigue threshold - ΔK th , coefficient in Paris equation - C, exponent in Paris equation - m p , fatigue crack growth rate - da/dN) are presented in Tab. 1, as shown also in [1,2]. Specimen K Ic [MPa  m] a c [mm] ∆K th [MPa  m] C m p da/dN [m/cycle] With reduced plasticity 46.3 9.3 7.4 5.7·10 -11 3.15 6.36·10 -08 With adequate plasticity 50.4 8.7 3.0 3.0·10 -11 3.02 5.11·10 -08 Minimum allowed value of K Ic for 20GSL at temperature below 0°C is K Ic = 41 - 44 MPa·m 1/2 Table 1 : Fracture mechanics parameters at 23°C, for the stress intensity factor range ΔK = 10 MPa  m. S TRESS STATE urbine runner cover at the hydro power plant ''Djerdap 1'' is presented in Fig. 1. Loading is defined for normal operation conditions, comprising combined action of pressure, axial force and torsion moment, as explained in [1]. Finite element mesh for axisymmertic model is shown in Fig. 2. The results, indicating max. stress 81.1 MPa, is shown in Fig. 3. a) q2 q q1 q q q2 q q1 b) Figure 1 : Vertical Kaplan turbine, with nominal output power of 200 MW. Figure 2 : Finite element mesh for axisymmetric model. T