PSI - Issue 2_A

Toshihiko Amano et al. / Procedia Structural Integrity 2 (2016) 422–429 Author name / Structural Integrity Procedia 00 (2016) 000–000

424

3

100 150 200 250 300 350 400 450

100

20 Shear area fraction ［ % ］ 40 60 80

Absorbed energy ［ J ］

0 50

0

-140 -120 -100 -80 -60 -40 -20 0 20 40

-140 -120 -100 -80 -60 -40 -20 0 20 40

Temperature ［ O C ］

Temperature ［ O C ］

Fig. 1. Charpy test results for base metal of the pipe; (a) absorbed energy and (b) shear area fraction

2.2. Drop-weight tear test (DWTT)

In order to investigate the effect of notch configurations on DWTT results with respect to the brittle-to-ductile transition curves, the shear area and the abnormal fracture appearances, three kinds of DWTT specimens were prepared. Fig. 2 shows the specimen configurations and notch types. The pressed notch DWTT (PN-DWTT) specimen is a standard specimen in API 5L/DNV standard. The chevron notch DWTT (CN-DWTT) is also standardized in API. The static pre-cracked DWTT (SPC-DWTT) is prepared using PN-DWTT specimen by conducting static three-point bending test. The details for static pre-cracking method are shown in following section. All DWTT specimens have initially same notch depth. All specimens were flattened and taken from transverse direction of pipe. Fracture surfaces were observed to evaluate shear area fraction and abnormal fracture appearances.

(a)

(b)

Notch Angle 45 o ± 2 o

PN

notch ((b))

Notch Depth 5.1 ± 0.51

CN

76.2 ± 3

Radius 0.025

Notch Depth 5.1 ± 0.51

90 o

305

SPC

19.1

Notch Depth 5.1 ± 0.51

Unit:mm

Static pre-crack

Fig. 2. (a) Dimension of DWTT specimens and (b) notch configurations; PN, CN and SPC

2.3. Static three-point bending test

The static three-point bending tests were conducted at room temperature in order to prepare the SPC-DWTT and the pre-strained materials. Fig. 3 shows a method of statically pre-cracking and measuring degrees of pre-straining. Static pre-crack was induced in the standard DWTT specimens with pressed notch (PN-DWTT) which had dimensions of 76.2 x 305 x 19.1 mm in transverse direction (Fig. 2 (a)). As shown in Fig. 3 (b), the load was applied until a drop in maximum load of approximately 1.25 % (Wilkowski et al., 2012). The surface of the PN-DWTT specimens was electrolytically-etched to print circle patterns with 5 mm in diameter in order to measure the plastic strain (Fig. 3 (c)). Fig. 4 shows an example of the strain distribution after the static three-point bend test in terms of (a) the plastic strain in the traverse direction, (b) the plastic strain in the propagation direction and (c) the equivalent plastic strain. The equivalent plastic strain  eq was evaluated from the strain components by Eq. (1);