Issue 35

G. Meneghetti et alii, Frattura ed Integrità Strutturale, 35 (2016) 172-181; DOI: 10.3221/IGF-ESIS.35.20 178 (a) 0° -45° -90° -135° 180° 135° 90° 45°  K=26.3 MPa·m 0.5  K=28.4 MPa·m 0.5  K=35.6 MPa·m 0.5  K=49.6 MPa·m 0.5  K=64.1 MPa·m 0.5 V_3 specimen 10 2 10 3 10 4 4·10 4 h [W/m 2 ] Crack (b) -45° -90° -135° 180° 135° 90° 45° 10 2 10 3 10 4 5·10 4 h [W/m 2 ]  K=31.5 MPa·m 0.5  K=36.7 MPa·m 0.5  K=78.7 MPa·m 0.5  K=98.0 MPa·m 0.5 V_4 specimen 0° Crack (c)  K=30.3 MPa·m 0.5  K=36.9 MPa·m 0.5  K=45.7 MPa·m 0.5  K=53.2 MPa·m 0.5  K=66.9 MPa·m 0.5 V_5 specimen 10 3 10 4 6·10 4 0° h [W/m 2 ] -45° -90° 180° Crack -135° 135° 90° 45° (d) 10 2 10 3 2·10 3 q [J/(m 2 ·cycle)]  K=30.3 MPa·m 0.5  K=36.9 MPa·m 0.5  K=45.7 MPa·m 0.5  K=53.2 MPa·m 0.5  K=66.9 MPa·m 0.5 V_5 specimen 0° -45° -135° 135° 90° 45° -90° Crack 180° 10 Figure 5 : Distribution of the thermal flux h along the boundary of the control volume for different  angles for (a) V_3, (b) V_4 (c) V_5 specimen and (d) and corresponding energy flux per cycle q of V_5 specimen. C OMPARISON BETWEEN EXPERIMENTAL AND THEORETICAL TEMPERATURES CLOSE TO THE CRACK TIP n analytical solution is available in order to evaluate the time-dependent temperature field in the case of a homogeneous and isotropic infinite plate with a time-independent heat generation h L distributed along a line in the thickness direction [18]. At the time t=0 when the heat generation starts, the temperature is supposed homogeneous and equal to T 0. Between time t=0 and t, the temperature variation  T(r,t)=T(r,t)-T 0 can be expressed by Eq. (11) [18]: 2 ( , ) 4 4 L h r T r t Ei t c                      (11) where Ei is the integral exponential function given by u x Ei e u du      and x= 2 4 r t c            . Since the major source of heat power is the cyclic plastic zone, the linear heat generation h L was applied in its centre, according to [3]. Fig. 6a shows the cyclic plastic zone idealised as a circle having radius r p . According to Irwin [20], the cyclic plastic zone radius in the plane stress condition is equal to: 2 ' ,02 1 2 2 p p K r               (12) A