Crack Paths 2009

polarization. The absorbed hydrogen diffuses in the specimen and reaches the crack.

The concentration of diffusible hydrogen was 1.32ppm at the polarized location and

0.21ppm at crack location. This arrangement enabled the continuous hydrogen charge

keeping the isolation of crack from electrolyte. Sulfuric acid whose pH was 2.0 was

used as the electrolyte. Cathodic polarization was done at current density of 174A/m2.

Crack propagation test was done in air at ambient temperature. The crack length was

measured by back face unloading elastic compliance method [4].

T E S TR E S U L T S

Crack Propagation under Triangular Stress Pattern

Crack propagation tests on material tempered at 843K which has medium strength and

is popularly used in engineering application were done using triangular stress pattern

shown in Fig.4. Loading period t was chosen

as 1800s. Crack propagation rate is shown Fig.5. The crack propagation rate was

σ

t

m a x σ

against stress intensity factor range Δ K in

max σ min σ

R =

accelerated by hydrogen absorption. At

σmin

stress ratio lower than 0.4, moderate acc leration ab ut six times occurr d as shown by open symbols. At stress ratio

time

Fig.4 Triangular stress pattern

10-3

10-3

SCM440H,Tempered at 843K

SCM440H,Tempered at 843K

t = 1800s

t = 1800s

10-4

10-4

H charged

H chargedR=00.4

R = 0

0.4

0.675

0.6

0.75

,d

,d

Uncharged

r 10-5 a t e

r 10-5 a t e

Uncharged

R = 0

R = 0

0.6

ag a t i o n

p ro p ag a o n t i

0.6

10-6

10-6

rpo

kp

10-7

10-7

C r a c k

r a c

C

20

50

5 10-8 100 Stress intensity factor range, Δ K (MPa m1/2) 10 20 50

10 10-8 200 Maximumstress intensity factor,Kmax (MPam1/2) 100

Fig.5 Effect of stress ratio on crack propagation rate und r t iangular st ess

Fig.6 Crack propagation rate under

triangular stress shown against Kmax

shown against Δ K

1027