PSI - Issue 5

Takahide Sakagami et al. / Procedia Structural Integrity 5 (2017) 1370–1376 Takahide Sakagami / Structural Integrity Procedia 00 (2017) 000 – 000

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3. Stress intensity factor evaluation based on the TSA technique

Fig. 1 Coordinates near crack front.

For a crack existing in semi-infinite plate as shown in Fig. 1, the equation of the sum of principal stresses around crack tip under mode I loading is given by the series expansion formula as follows. + = (√ 2 cos 1 2 ) + 2 + (√ cos 1 2 ) 3 + ⋯ (2) In this study, the first term coefficient K in Eq. (2) was calculated by the least square fitting using numerous data of the sum of principal stresses obtained by TSA technique, thus stress intensity factors K can be determined. Experimental studies were conducted for a steel plate specimen having an out-of-plane gusset plate as shown in Fig. 2. This specimen modeled a part of the orthotropic steel deck structure constituted by the deck plate and the vertical stiffener. The specimen was loaded by a fatigue testing machine as shown in Fig. 3 developed by Yamada et al. (2007). A plate bending loading was applied to the specimen being fixed one end of the specimen on the trestle. The other end of the specimen was subjected to cyclic loading by the shaker with a decenterizing spindle. Constant amplitude loading was applied to the specimen. The applied stress range was measured by the strain gauge installed on the specimen. The stress ranges initially applied to the specimen were set at 60, 80, 100 and 120 MPa with a stress ratio R =0. Crack propagation test was conducted before the fatigue crack penetration to the back surface. Crack penetration was detected by the breaking of fine copper wire installed on the back surface. Flat black paint was applied to the specimen surface to avoid reflection and to increase the emissivity. An infrared camera with a QVGA InSb array detector (Type SC7500 by FLIR company, NETD: 20mK) was employed for the infrared measurement. The stress intensity factors were calculated from stress distributions measured by TSA technique, and the relationship between stress intensity factor ranges and crack propagation rates were obtained. The obtained results are shown in Fig. 4. It is found that the obtained relationship shows a good correspondence with the Paris law. 4. Experimental study for laboratory specimen

Fig. 2 Steel plate specimen having an out-of-plane gusset plate