200 P. Tayefi et al. Fig. 26.4 Post-crush of ‘perfect’ specimen As Fig. 26.3 shows evidence of bonding beginning to take place it was assumed that the crack growth would be visible if non-destructive methods of analysis were used to observe the crack growth (i.e. leak paths) of joints failed to the fatigue testing regime highlighted in Fig. 26.2. 26.4 Ultrasound Experiment A rig was designed and built to observe the leak paths of failed joints. The rig consisted of an ultrasonic focussing lens attached to a stepper motor stage (Fig. 26.5). The stepper motor stage allowed for line scans to be performed. Joints that have been tested to failure in the fatigue programme (Fig. 26.2) were cut in half using a bandsaw, along the centre line of the pipe. This left the internal bore and the underside of the tapping tee exposed so that the ultrasonic transducer could focus on the internal bore of the pipe. Furthermore, the focussing lens transmitted pulses perpendicular to the internal bore of the PE pipe and fitting assembly. Preliminary line scans were conducted on the internal bore of the pipe in order to observe the delaminated surface of the fusion interface. The line scans were then knitted together to create a map of the fusion zone thus observing the leak path (Fig. 26.6). Once the map was created, the predicted leak path was confirmed by applying a flow of water through the EF tapping tee fitting. This was achieved using a basic hand pump.
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