Fatigue Crack Paths 2003

Table 2. The curve fitted coefficients A DOB,i and exponents ai , bi and ci in Eq 6, when

Δσm≥0.

i

1

2

3

4

5

6

7

8

9 10

A0,i

4.01 -7.71 33.04 -144.2 7.35 -33.20 64.45 192.5 -17.68 -0.438

A± ,i

-3.27 11.78 -2.25 -0.22 -4.11 12.66 -55.80 23.57 8.90 4.96

A0.5,i

-2.18 -3.18 -3.00 16.76 -4.48 -18.71 34.67 -35.73 8.61 1.80

A-0.5,i

-3.1 -2.72 -45.67 208.1 -7.63 -6.23 20.86 -311 21.16 -4.03

ai

1

0

0

0

1

0

0

0

1

2

bi

0

1

0

0

1

2

1

0

0

0

ci

2

2

3

2

1

1

1

1

1

1

i

11 12 13 14 15 16 17 18 19 20

A 0,i

-21.27 -116.6 315.1 -286.7 18.98 -2.44 -15.89 8.88 10.51 -2.99

A ± ,i

-106.0 12.50 27.55 -73.99 103.8 38.10 44.87 -10.00 25.23 -22.71

A 0.5,i

-24.95 -107.8 285.6 -264.0 33.07 0.378 95.44 -8.30 12.63 -6.29

A -0.5,i

11.15 234.7 -365.0 46.54 16.57 -6.56 220.6 -42.27 48.66 -17.64

ai

1

0

0

0

1

2

0

1

2

3

bi

2

3

2

1

1

1

0

0

0

0

ci

0

0

0

0

0

0

0

0

0

0

DISCUSSIOANN DC O N C L U S I O N S

The fatigue behaviour of one-sided partially penetrating butt weld in corner was

investigated by using the 2D linear elastic fracture mechanics calculations. The J

integral method, maximumtangential stress criterion, and Paris' crack growth law were

used to predict the fatigue strength. It was assumed that the fatigue life of the joint could

be described by the propagation of pre-existing straight-fronted cracks. The initiation

period, the semi-elliptic crack-front shape of an initial fatigue crack and the threshold

value of stress intensity factor were not taken into account. The whole stress range was

assumed to be effective. This should lead to conservative fatigue strength estimates. An

initial crack depth of 0.2 m mwas assumed for the toe cracks. In finite element model

the main plate is free to bend inside the base plate. This should take into account the

effect of possible small cap between the plates. Identical fatigue behaviour was assumed

for both the weld metal and the parent material. On the basis of these assumptions and

fracture mechanics analyses, the following conclusions can be drawn:

(1) Theoretical fatigue strength values for the weld root crack length to plate thickness

ratios of w/t = 0.008 - 1.0, for weld height to plate thickness ratios of h/t = 0 - 1.25, and

for base plate thickness to main plate thickness ratios of T/t = 1.0 – 2.0 were calculated.

The load condition was varied from pure tension loading to pure bending loading and to

the combined tension/bending momentloading. Both bending directions were analysed

for Δσm≥ 0 and for Δσm< 0.