PSI - Issue 13

Yasuyuki Furuta et al. / Procedia Structural Integrity 13 (2018) 110–115 Furuta / Structural Integrity Procedia 00 (2018) 000 – 000

111

2

The above technology should be studied by relevant engineers and students. However, a pipe burst test costs 10 4 to 10 6 US dollars; it is almost impossible to conduct it as an educational purpose. From this standpoint, the authors have developed a simulated running ductile fracture experiment using rubber tubes. The experiments have been conducted as project-based learning programs in Brazil and Japan. The present paper describes an outline of the experiment and discuss the mechanism of propagation and arrest of running crack in rubber tubes. Crack propagation behaviors of rubber balloons or tubes were studied by Stevensen and Thomas (1979), Moulinet and Adda-Bedia (2015) and Lawrence et al. (2015). Lawrence et al. (2015) found that crack velocity agreed with terminal crack velocity which is close to the transverse wave velocity; it changed with circumferential stress due to non-linear elastic behavior of rubber. Dependence of the terminal crack velocity on elastic modulus is discussed in detail by Broberg (1999). But, their experiment was conducted at sufficiently high pressure and they did not discuss crack propagation well below the terminal crack velocity or crack arrest in rubber tubes. The present experiment is aimed at understanding the interaction between gas decompression and crack propagation at relatively low pressure so as to simulate crack propagation and arrest in actual pressurized pipes. Commercial rubber tubes, Qualatex 350Q TM , were used for this purpose. The tube was pressurized by a manual pump and static pressure was measured and controlled by a digital pressure gauge. Note that relative pressure is used throughout the present study. Tube diameter and length was 60 to 85 mm and 1 m or more, respectively at pressure of 0.003 to 0.013 MPa. Crack was initiated by stinging the tube by a needle. The crack propagation was monitored by high-speed camera, PHOTORON SA-1.1, with 20,000 to 100,000 frames per second. The pressurizing gas was essentially the air, but helium gas was also used. 2.2. Experimental result Figure 1 shows behavior of crack propagation in the air test at initial pressure 0 = 0.0067 MPa. The crack propagated in the axial direction through the whole tube length. Average crack velocity between 200 to 500 mm crack length was 229 m/s. Figure 2 shows crack propagation behavior in the helium gas test at initial pressure 0 = 0.006 MPa. Average crack velocity was 174 m/s, which was smaller than that of the air test. It should be noted that crack opening profiles were similar to those of full-scale burst tests of pipelines although radial movement of pipe wall is significant in the full-scale tests. 2. Experiment 2.1. Experimental method

Fig. 1 Crack propagation behavior, air test, 0 = 0.0067 MPa.