Issue34

A. Tajiri et alii, Frattura ed Integrità Strutturale, 34 (2015) 347-354; DOI: 10.3221/IGF-ESIS.34.38 350 crack as 0.5 (semicircular crack), and using Newman-Raju equation [9]. It should be noted that crack growth rates become higher in the as-received, L and H specimens in the increasing order. Based on the S-N diagram (Fig.3), it can be said that the crack initiation resistance of the as-received material was improved by FSP, while d a /d N - K max relationship (Fig.6) reveals FSP has detrimental effects on the crack growth resistance. Figure 4 : Fracture surfaces near crack initiation site in the as-received material ( σ a =140MPa, N f =2.81×10 5 ). Figure 5 : Fracture surfaces near crack initiation site in the FSPed materials; (a) L specimen ( σ a =170MPa, N f =1.62×10 5 ), (b) H specimen ( σ a =180MPa, N f =4.23×10 4 ). Figure 6 : Relationship between crack growth rate, d a /d N , and maximum stress intensity factor, K max . 100  m 50  m 50  m (a) (b) 1 2 3 4 5 6 7 10 −6 10 −5 10 −4 H as−received Crack growth rate da/dN (mm/cycle) Maximum stress intensity factor K max (MPa √ m) L A356 Plane bending R = −1