Crack Paths 2009

uncharged material was about one thous nd. The critical c nditio mapthat caused sudden accelerati n

1020

923K

S C M 4 4 0 H Hcharged Temper(K)4 3

80

8038473 3

is shown in Fig.12. The acceleration wa dependent on temperi g

903

temperature and stress ratio. Popularly used medium strength steel s well as hard material was enhanced by hy rogen. Soft material which was t pered at 923K as not enhanced by

2460

843

923

903K

84043K

0

0.2

0.4

0.6

0.8

1

hydrogen.

Stress ratio, R

Fig.12 Onset of acceleration of crack

Time-dependent Crack Growth Crack propagation test using

propagation under triangular stress

trapezoidal stress pattern shown in

σ

tH

60s

Fig.13 was done to examine the participation of tim -dependent crack growth in the sudden

m a x σ min

min R σ

σ

=

m a x σ

time

acceleration. Test result is shown in

Fig.13 Stress pattern for time-dependent

Fig.14 for R=0.6. Hold time was

crack propagation

Hold

Hold

Fig.15 Effect of tempering temperature SCM440H 20 50 Temper(K) 80473 )

Tempered at 843K R = 0.6 20 Uncharged H cTrairagnegdle t= 1800s Hold tH 72 H 180 S C M 4 4 0 H

50

17182800s0s

/yc c le

10-3 10 1 87654

923K 100

200

803K

843K

980733KK

903

(m

a c k p r o p ag t i o n r a t e , d

a c k p r o p ag t i o n r a t e , d

923 Temper(K) Triangle

89047023

( t=1800s,R=0.6)

C r

10-2 200 Maximumstress intensity factor, Kmax (MPam1/2) C r

Maximumstress intensity factor, Kmax (MPam1/2)

Fig.14 Time-dependent crack propagation n material tempered at 843Kunder stress hold 10 100 10-87 -6 543

on time-dependent crack propagation

under stress hold (t=1800s, R=0.6)

1030