Crack Paths 2009

10μm

(b)803K, K max =53MPam1/2

(a)443K,Kmax=16MPam1/2

Fig.9 Effect of tempering temperature on fracture

surface for triangular stress R=0.6, t=1800s

which is a very hard material, the morphology was intergranular. On the contrary, the

morphology in other materials was quasi cleavage.

In the case of 843k tempered material which has medium strength, the sudden

acceleration was experienced only at high stress ratio as shown above. This kind of

acceleration is expected even at lower stress ratio in harder materials. Therefore, tests at

various stress ratios including low stress ratio were done using 443K and 803K

tempered materials. Test results are shown in Fig.10 and 11. Sudden acceleration was

experienced at all stress ratios including R=0. The acceleration ratio compared to the

10-3

( 10-43

/yc c le )

S C M 4 4 0 H Temperedat 803K

R0.246705

Temperedat 443K S C M 4 4 0 H

( 10-4

▲〇 0R0.4

/yc c l)e

m

m

10

100

10-87

Tempered ■at 8403.7K5

-6 10-5

200

o n r a te , d

pa g a o n r a t e , d t i

R

Uncharged

Uncharged R=0

10

20

Tempered at 843K R=0

t i

10-876

5

50

ag a

prpo

R=0.6

por

a c k

0

a c k

R=0.6

0.4

C r

10-5 100 Maximumstress intensity factor,Kmax (MPam1/2) C r 0.75

20

50

)

Maximumstress intensity factor, Kmax (MPam1/2

Fig.11 Effect of stress ratio on crack

Fig.10 Effect of stress ratio on crack

propagation of material tempered at

propagation of material tempered at 443K

803K(triangular stress, t=1800s)

(triangular stress, t=60s)

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