Issue 43

F. Berto et alii, Frattura ed Integrità Strutturale, 43 (2018) 1-32; DOI: 10.3221/IGF-ESIS.43.01

Figure 10: Through-the-thickness SED distribution for t/a = 0.50, 1, 2, 3. Control radius R 0

= 1.00 mm.

Some FE analyses were carried out under plane strain conditions by modelling cracks of different length in an infinite plate and using two values for the radius R 0 , 0.02 mm and 0.2 mm, respectively. Elastic properties were kept constant, E = 206000 MPa and ν =0.3. The toughness is thought of as correlated to the inverse of the mean value of strain energy, 1 W . Fig. 11 plots 1/ 1 W as a function of the crack amplitude a. The plateau on the left hand side of Fig. 2 is due to the fact that the small cracks are fully embedded in the elementary structural volume, so that the value of 1 W coincides with that of the points far away from the crack, )E2/() 1( 2 2 0   , where (1-ν 2 ) is due to plane strain conditions in the FE model.

Figure 11: Influence of crack amplitude on finite-volume-energy (plane strain, infinite plate).

where Δ σ 0

Under fatigue limit conditions we introduce ∆K th

and Δσ 0

into Eq.(1) ,

is the plain specimen fatigue limit and

Δ K th the threshold value of the stress intensity factor range for long cracks under Mode I conditions. Now the critical radius becomes:

10