PSI - Issue 6

Tonsho Fumiaki et al. / Procedia Structural Integrity 6 (2017) 269–275 Author name / Structural Integrity Procedia 00 (2017) 000 – 000

271 3

30

A

350

EBW

500

B

149[mm]

C

>1500 >300

Fig. 1 Configuration of whole specimen

1000 1200 1400 1600 1800 2000

1000 1200 1400 1600 1800 2000

1000 1200 1400 1600 1800 2000

the obvious crack bifurcation starts to generate

0 200 400 600 800 Crack velocity, v [m/s]

0 200 400 600 800 Crack velocity, v [m/s]

0 200 400 600 800 Crack velocity, v [m/s]

Fig. 2 Schematic illustration of the instrumentation

specimen #5 homogenousmaterial

soft welded joint specimen #2

specimen #3 soft welded joint

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Crack length, a [m]

Crack length, a [m]

Crack length, a [m]

Fig. 3 Comparison of crack propagation velocity

Table 3 Test conditions

Part B

Homogenous /Soft welded joint Soft welded joint Soft welded joint

#

Part A

Experimental Condition

100MPa/-100 °C 300MPa/-100 °C

Material

Width[mm]

#2 #3 #5

High-nickel steel High-nickel steel

N30 N30 N30

30 20 30

Homogenous 300MPa/-100 °C Crack gauges and strain gaugescan detect the passage of thecrack, so from these gauges the crack propagation velocity was calculated (Fig.3). The velocity measured in the material with soft welded joint is lower in the beginning of the propagation and higher in the end of the propagation than the velocity measured in the homogenous material. Final speed in the material with soft welded joint is accelerated to more than 1800m/s. This is thought to be the result of concentration of the strain in the soft material centered in the specimen. Fig.4 shows the schematic picture of the crack path in each specimen. The point is observed on the way of propagation where the fracture surface becomes uneven and the obvious crack bifurcation starts to generate . Surface roughness was measured with the laser displacement meter (Fig.5). Surface roughness is valued by standard deviation. It is shown that surface roughness gets more apparent after the crack bifurcation. From these data, the meandering of the crack and surface roughness occurs when the crack speed gets around 800m/s. However, according to the previous study on elastic dynamic fracture theory, crack branches at subsonic speed. To examine N30