Fatigue Crack Paths 2003
same, that is, the SIFs tend to increase because of the notch presence. Such an increase
varies with the crack geometry. The maximumvalue of SIF, along the crack front, is
attained at either the deepest point (A) or the near-surface point (C), depending on the
values of both ξ and α.
The dimensionless SIFs for both tension and bending are shown against
t K in Fig. 4,
for different crack configurations. It can be noted that, depending on both crack
geometry and loading conditions, SIF values may either increase, or decrease or have a
non-monotonic trend with increasing
t K , the values of the other parameters being the
same.
1.2
20
ξ= 0.8
ξ= 0.5 P O I N T A(ζ∗=1.0) N T C( 0.1
0.α60
4.0
16
P O I N T (Aζ∗=1.0)
P O I N T (Cζ∗=0.1)
1.0
0.0
3.0
α
ξ= 0.1 P O I N T (Aζ∗=1.0) N TC ( 0 1
0.0
α
0.4
0.0 0.6
1.0
0.0
0.6
0.6
0.0
0.8
12
2.0
1.0
F
=KI,
1.0
0.6
0.6
/
1.0
F
K*I,
0.6
48
01.0
1.0
(c)
(a)
(b)
1.0
345
α
ξ=0.1 P O I N T A(ζ∗=1.0) C 0.1)
α
1.25
ξ=0.5 P O I N T A(ζ∗=1.0) T (Cζ∗= 0.1
0.6
0.0 0.6
0.0
0.0
1.0
1.0
α 0.0
0.0
01.60
0.6
0.6
/
0.8
ξ= 0.8
0.0
x
1.0
I , M
P O I N T (Aζ∗=1.0)
K
P O I N T (Cζ∗=0.1)
=
0.6
x
,M
12
*I
(e)
1.0 K1.2
(d)
(f)
1.0
1.5
2.0
2.5
3.0
S T R E SCSO N C E N T R A TF IA COTNO RK,t
0.46
1.0
1.0 3.0 S T R E SCSO N C E N T R A TFIAOC TNO RK,t 1.5 2.0 2.5
01.0257005050
1.0
1.0 2.5 3.0 S T R E SCSO N C E N T R A TFIA OC TNO RK,t 1.5 2.0
Figure 4. Dimensionless SIF vs SCFat point A and point C on the crack front:
(a) to (c) tension; (d) to (f) bending.
F A T I G UCE R A CGKR O W T H
N o wthe fatigue propagation paths of the above surface flaws in notched bars under
tension or bending loading are determined by applying a two-parameter theoretical
model [7]. According to such a model, the crack front lying on an ellipse with semi
axes a and b grows after one cyclic loading step to a new configuration described by the
following equation :
2
2
x
+ y
1
(3)
=
*)( b
*)( a
2
2
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