Issue 35

R.A. Cardoso et alii, Frattura ed Integrità Strutturale, 35 (2016) 405-413; DOI: 10.3221/IGF-ESIS.35.46 409 The results from these tests are reported in Tab. 3 and the crack path is described according to the scheme sketched in Fig. 5. Figure 5 : Crack path scheme. AISI 1034 1,000,000 cycles ܽ 1 =68 μm θ 1 * =30° 35NCD16 100,000 cycles ܽ 1 =105 μm θ 1 =17° 250,000 cycles ܽ 2 =130 μm θ 2 =13° 500,000 cycles ܽ 3 =248 μm θ 3 =11° * The angle measured by [14] was established through a series of tests, where an angle of 30° ±3 was observed. Table 3 : Crack path configuration. R ESULTS FOR CRACK INITIATION ORIENTATION Crack initiation direction for AISI 1034 n this case we have a material characteristic length given by 53.5 μm, Eq. (1). The results of the critical direction method are shown in Fig. 6. As can be seen, the estimated angle is very small when the maximum value of Δ σ n,eff (only positives values of normal stress are taken into account) is considered, whereas max(Δ σ n ) and min(Δτ) provide similar results. The range of angles that were investigated were limited to -60° to 60°, as (i) it doesn’t make sense physically to assume crack propagation in directions larger than this (shallow angles practically parallel to the surface) (ii) it reduces the computational cost involved in the calculation when more complicated geometries that requires FEA analysis are assessed. Figure 6 : The critical direction method for AISI 1034 data. Considering the complexity of the stress field and the dispersion involved in the calculation of material parameters as L , the critical direction criteria based on max(Δ σ n ) and min(Δτ) provided quite reasonable results in the estimative of the I