PSI - Issue 2_A

Jaewoong Jung et al. / Procedia Structural Integrity 2 (2016) 2989–2993 Author name / Structural Integrity Procedia 00 (2016) 000–000

2992

4

(c)

(b)

(a)

Fig. 3. SEM micrographs of the fracture surfaces near crack initiation site: (a) untreated; (b) treated by 90 A/mm 2 ; (c) treated by 150 A/mm 2 . The arrow marks indicate the local melting site.

3.3. Fatigue crack growth behavior Fig. 4 (a) and (b) show the relationship between the fatigue crack growth rates, d a /d N , and maximum stress intensity factor, K max , obtained by applying electric current with the density level of 90 A/mm 2 and 150 A/mm 2 , respectively. In the figures, the arrow marks indicate the application points of the electric current. The fatigue crack growth behavior of the specimen applied electric current was compared to the result of untreated specimen. Every fatigue crack was initiated on the surface of the specimen. In the result with the electric current level of 90 A/mm 2 , the growth rates of fatigue crack were slower than those of untreated one. The significant delay effect just shows after the application of electric current. Especially, in low K max region, the rates were decreased due to the effort of

(a)

(b)

10 −3

10 −3

A6061−T6

A6061−T6

Current level of 150 A/mm 2

Current level of 90 A/mm 2

10 −4

10 −4

−8 Crack growth rate d a / d N (mm/cycle) 10 −7 10 −6 10 −5

−8 Crack growth rate d a / d N (mm/cycle) 10 −7 10 −6 10 −5

Without pulsed electric current With pulsed electric current Current applied point

Without pulsed electric current With pulsed electric current

Current applied point

10

10

0.1

1

10

0.1

1

10

Maximum stress intensity factor K max (MPam ) 1/2

Maximum stress intensity factor K max (MPam ) 1/2

Fig. 4. Fatigue crack growth rates as a function of the maximum stress intensity factor for the specimens with and without electric current: (a) 90 A/mm 2 ; (b) 150 A/mm 2 .