Crack Paths 2012

well as the whole testing for SEB2was performed in a servo-hydraulic machine at a

frequency of 5 Hz. In contrast, all SE(T) specimens were tested in the resonant testing

machine at a frequency of about 110 Hz, at gradually decreasing load amplitude to

attain moderate crack growth rates. Both fatigue pre-cracking and crack growth tests

were performed at the load ratio of R = 0.1, at room temperature.

Table 1. Geometrical parameters and test conditions for SE(B) specimens

Span

FreqHuzency S

Lomaoddineg Specimen, test phase

amin m…mamax

parameters, m m s1 s2

loUapd,pekrN Nominal tensile

stress, M P a

SEB1

6 … 2 4

110

90

12

SEB2 3

6 … 2 4 6…10/10…27.5 110/5 160 80 80 5

36 24

I

270 18

SEB5

6…18.7/ 18.7…30.5

90

110/5

24

SEB6 7

36 48

I+II

6…12.1/ 12.1…26.5 6…26 2

110/5 5

160 40 120

135 80

SEB4/1

90

32

90

6…12.6

110

120 30

(2 sIt+aIgIes)

SEB4/ 2 8

135 90

12.6…23.5 12.5…26

110

80 40 40

36 24

SEB8/1

6…12.5

90

110

160 40 120

24

Table 2: Geometrical parameters and test conditions for SE(T) specimens

Hole parameters, m m Ø (graUdupaplleyrldoeacd,reaksiNng)eNominal tensile

Lomaoddineg Specimen amin m…mamax FreqHuzency

stress, M P a

SET1

6.1…30.6

110

10

10

24.6 Æ 10.6

61.5 Æ 26.5

SET2 3

6.1…29.9 6 3 0

I+II

110

10

10 8

I

SET4

6 … 2 5

110

-

-

26 Æ 10

65 Æ 25

Both SE(B) and SE(T) specimens shown in Figure 1 allow for testing at mode I and

mixed mode loading conditions. Three bend specimens referred to as SEB1, SEB2and

SEB3were tested under pure mode I loading with symmetrically positioned supporting

rollers (s1=s2 = 80 mm). Further three specimens denoted as SEB5, SEB6and SEB7

were subject to mixed mode loading by asymmetrically placing the lower rollers with

the span values equal to S = s1 + s2 = 160 m mand s2/s1 = 3. Twoadditional specimens,

SEB4and SEB8, were tested following two consequent steps: first, asymmetric loading

with s2/s1 = 3 was applied up to a crack depth of some 12.5 m m proceeded by

symmetrical loading of a resulting curved crack at s1 = s2 = 40 mm.

Mixed mode loading for the SE(T) specimens was achieved by machining a hole of

10 m mdiameter in the central part of the specimens after pre-cracking, similar to the

approach in [12]. The hole was centred with respect to the specimen width but shifted

some distance with respect to the original crack plane. The eccentricity parameter e, i.e.

the distance from the hole centre to the pre-crack plane, was equal to e = 10 m mfor the

specimens SET1 and SET2, and e = 8 m mfor the specimen SET3, respectively.

Additionally, one specimen without hole drilling, denoted as SET4, was tested under

pure modeI conditions.

Geometrical parameters and loading conditions for the bend and tension specimens

considered in this study are summarized in Table 1 and Table 2, respectively. Note that

throughout the paper the crack size a represents the projection of the crack path on the

initial pre-crack plane.

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