Crack Paths 2009

where the upper index (i) points subsequent specimen; (j) is a total number of

specimens. The estimator Em determines general location of points in 2D space Nexp -

Ncal. The estimator Estd determines magnitude of data scattering. The weight function

parameter ln is analysed in a wide range. For each value of ln integration process is

performed and fatigue estimators (3) are calculated. Figure 4a presents distribution of

estimators (3) over the parameter ln. The higher value of ln the stronger non-locality

effect is considered and as a result longer calculated fatigue life is obtained. The best

estimation ()(mineqlEn ) for AISI steel in (AF) state for both notch radius is received for

ln=0.17 m m(Fig. 4b).

(a)

(b)

5 106

Em = -0.07 std 0.15

Eeq =0.165 ln = 0.17 m m

Kt=2.8

, -

-0-.0101.51501

0.15

0.2

0.25

,yc c l e s

eq

10 4

, E

d

,E s t

N c a l

E m

l n , m m

0.02.523

×2.0 ×2.0

E m Esetqd

104

105

106

K t =1.8

N ,cycles

exp Figure 4. (a) Distribution of fitting estimators, (b) comparison of the e erimental Nexp and calculated Ncal

fatigue lives for AISI 1141 (AF) steel for ln=0.17 m m

Whereas, for AISI steel in (QT) state the best estimation is received for ln=0.43 m m

(Fig. 5).

(a)

(b)

6

10

0.2

E

= -0.04

m

E std =0.12

0.15

E eq

=0.128 ln=0.43mm

0.1

, -

,cycle s

e q

5

10

0.05

, E

s t d

N c a l

0

, E

E m

-0.05

×2.0

E

m

×2.0

4

10

Estd

-0.1

K

=1.8

t

E eq

-0.15

0.35

0.4

0.45

0.5

10 4

10 5

10

6

ln, m m

N exp

, cycles

Figure 5. (a) Distribution of fitting estimators, (b) comparison of the experimental Nexp and calculated Ncal

fatigue lives for AISI 1141 (QT) steel for ln=0.43 m m

The differences in ln parameter must be seen as a result of different material properties

of cyclic plasticity (tab.1). Cyclic hardening curves of AISI steel are different for (AF)

σa AISI steel in (QT) state

and (QT) states (Fig. 6). For the same stress amplitude

exhibits larger strains than in (AF) state. It means that AISI steel in (QT) state has larger

ability to dissipate energy by plastic strains. The field of plastic strains slows downthe

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