Crack Paths 2012

Fig. 4b, in order to introduce the fatigue crack starter notch (1) inside the Base Material

(BM), (2) in the Weld Metal (WM)centre, (3) in the Heat Affected Zone (HAZ)along

the weld bead. After machining, the specimens were grinded and polished to facilitate

the monitoring of the crack advance.

Figure 4. (a) Geometry of C(T) specimens used in this study. (b) Extraction scheme

from the welded plates.

Fatigue CrackGrowthTesting

The fatigue crack growth testing was performed according to the standard A S T ME647

08. The experiments were conducted in the laboratory environment on a servo-hydraulic

testing machine. A sinusoidal pulsating (load ratio R = 0.1) load waveform was applied

at a frequency of 30 Hz. During fatigue testing, optical microscopy (travelling

microscope) was used for crack length monitoring.

Fracture Toughness (J-Integral) Testing

The fracture toughness testing was performed according to the standard A S T ME1820

09. The specimens were fatigue pre-cracked in the laboratory environment using a

resonant testing machine with load ratio R = 0.1 keeping the maximumstress intensity

factor less than 24 M P a m T.he initial crack length to specimen width ratio (a/W) was

about 0.45. Subsequently, to enforce the plane strain condition, 20%side grooves were

introduced, resulting in a net thickness (BN) of 12 mm.The single specimen method was

adopted to determine the J-resistance curve JR. The crack opening displacement was

recorded by a C M O Dclip gauge during constant displacement rate (0.5 mm/min–

under displacement gauge control). The crack length was measured by the compliance

technique and verified by post-test optical crack size measurements. For this purpose, in

order to minimize the effect of load relaxation on the compliance measurements,

causing a time-dependent nonlinearity in the unloading slope, the specimen was held at

a constant C M O fDor 1 min dwell time up to force stabilization prior to initiating the

unloading.

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