PSI - Issue 13

Yoshitaka Nara et al. / Procedia Structural Integrity 13 (2018) 222–225 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

224

3

3. Rock sample

As mentioned before, we used Berea sandstone (Ohio, USA, Mississippian period) as a rock sample in this study. This rock sample has been used in the previous studies (Nara et al., 2011, 2012, 2014). In Fig. 3, photomicrograph of Berea sandstone is shown. This photomicrograph was obtained under crossed nicols. Fig. 4 shows the X-ray diffraction (XRD) pattern for Berea sandstone. From this figure, it is recognized that the distinct peaks of quartz are remarkable. It is also recognized that the peaks of clay minerals are not remarkable. P-wave velocities in Berea sandstone in three orthogonal directions were 2.3, 2.3 and 2.2 km/s, which were measured by the ultrasonic transmission method. Young ’ s modulus and Poisson ’ s ratio were 8.20 GPa and 0.25, respectively, which were measured by uniaxial compression tests at 10 -5 s -1 strain rate with loading parallel to the bedding plane. Porosity was 20.4%, which was measured by water saturation.

Fig.4 XRD pattern of Berea sandstone. 㻌

Fig.3 Photomicrograph of Berea sandstone. 㻌

4. Results

In Fig. 5, the relationships between the crack velocity and the stress intensity factor are shown. In this figure, the relationships obtained in distilled water and the calcium hydroxide solution (Ca(OH) 2 ) with the concentration of 600 mg/L are shown. Figure 5 shows that the crack velocity at a constant stress intensity factor tends to be lower in Ca(OH) 2 .

10 -1

, ,

,

: in distilled water (325K, pH = 5)

: in Ca(OH) 2 (320K, pH = 12)

10 -2

10 -3

10 -4

10 -5

10 -6

Crack velocity [m/s]

10 -7

Berea sandstone

10 -8

0.15

0.2

0.25

0.3

0.35

Stress intensity factor [MN/m 3/2 ]

Fig.5 Relationship between crack velocity and stress intensity factor for Berea sandstone. 㻌