Crack Paths 2009

These results allow drawing a material failure curve called also material master curve. A

linear relationship was found

aT

K

cef c = + ,

b

(12)

,ρ

with a and b material constants which are a = -0.069 and b =77.28 for X52 steel. The

master curve is a way to take into account the constraint effect on the fracture toughness

and is associated with the driving force diagram in order to establish fracture conditions.

W e have analyzed the measured fracture toughness for different precracked

specimen geometries published in 4 references [11, 20-22]. Results are presented in

table 3 which includes our results obtained for notched specimens. All results are

coherent and indicate the following: tensile specimens have always higher fracture

toughness than bending specimens. This is due to high negative T-stress values for

tensile specimens and consequently lower constraint.

Table 3. Comparison of the fracture toughness for different specimen geometries.

references

specimens

Fracture toughness

[11] A S T M719 Grade A steel

CT(a/W=0.5), S E N B(a/W=0.5)

S E N B > C T

[19] ASI 1405- 180

SENT(a/W=0.5); SENB(a/W=0.5) D E N T(a/W= 5), C C T W=0.5), C T (a/W=0.6),

D E N T> C C T > S E N T

>SENB~ C T

[20] F Y OH Y 10 Alloy steel

S E N T(a/W=0.65), SENB(a/W=0.61), D E N T

SENT>SENBD>E N T

(a/W=0.61),

C T ~ D C B > S E N T

[21] P M M A SENT(a/W=0.3-0.6), C T(a/W=0.3- 0.7), D C B(a/W=0.1-0.7),

S E N T(a/W=0.5), C T(a/W=0.1;0.3; 0.5), D C B(a/W=0.5), T R(a/t= 4 ;

Present results

SENT>CT>RT>D C B

0.5 ; 0.6)

Crack stabilisation or bifurcation according to the Tef -stress

range for each specimen type is reported in table 4 (yσ is the yield stress).

The cefT,

range for different specimen configuration.

Table 4. T ce, f

Specimen SENT C T

R T

D C B

range -0,74

y σ ; - 0.53

y σ ; - 0.25

y σ ; 0.19

cefT,

y σ ;

-0.80

-0.67

-0.30

0.21

y σ

y σ

y σ

y σ

211