PSI - Issue 42

Litton Bhandari et al. / Procedia Structural Integrity 42 (2022) 529–536 Bhandari et al. / Structural Integrity Procedia 00 (2019) 000–000

534

6

Fig. 6. Defects based stress-life curve

(a)

(b)

(c)

(e)

(f)

(d)

Fig. 7. Fatigue fracture features (a) Crack initiation zone (b) Crack propagation zone (c) Fast fracture zone ; Frequently observed defects (d) Porosity (e) Unmelted powder particles (f)) Lack of fusion

concentration associated with them (Gaur et al. (2018, 2020)). Majority of the fracture area was covered by the crack propagation zone. The fast fracture zone is characterized by the dimples occurred due to coalescences of microvoids. The Gumbel distribution has been employed to evaluate the extreme value statistics of the crack initiating defects. The defect parameters ( √ area ) were arranged in increasing order. The maximum crack initiating defects’ size was then evaluated using Gumbel extreme value statistics (Features et al. (2014))). The reduced variate to represent the cumulative extreme value statistics is given by :

V i = − ln ( − ln ( R i ))

(1)

Where, R i = i / (n + 1), n is the total number of fractured specimens and i is the rank of the defects arranged in ascending order. The relation between reduced variate ( V i ) and defect parameter is almost linear with R 2 of 0.902 as shown in Figure 8 and thus, indicates that the distribution of crack initiating defects follows Gumbel distribution. The maximum crack initiating defects’ size was found to be 137 µ m.