Issue34

A. Tajiri et alii, Frattura ed Integrità Strutturale, 34 (2015) 347-354; DOI: 10.3221/IGF-ESIS.34.38

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.

100  m

Figure 4 : Fracture surfaces near crack initiation site in the as-received material ( σ a

=140MPa, N f

=2.81×10 5 ).

(b)

(a)

50  m

50  m

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 ).

10 −4

A356 Plane bending R = −1

10 −5 Crack growth rate da/dN (mm/cycle)

H as−received L

10 −6

1

2

3 4 5 6 7

Maximum stress intensity factor K max (MPa √ m)

Figure 6 : Relationship between crack growth rate, d a /d N , and maximum stress intensity factor, K max .

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