Location was determined from the difference in times of arrival of the two outer sensors, t. In addition, the speed of sound of the extensional wave or the time it takes for sound to travel between the outer sensors, tx, was required, where x is the distance between the two outer sensors. The speed of sound (tx/x) increases throughout the test as damage develops [6,24]. This was accounted for by determining the tx from events which occurred outside the outer sensors, presumably in the grips [25]. There was a period of no AE activity between 100,000 and 130,000 s (Figure 4a). For the following, only the location **data** after 130,000 s is presented since it leads up to failure. The location of the events prior to 100,000 s were evenly distributed across the gage section. The AIC derived t values typically differed less than 1 s of the actual first peak t. However, to get the most accurate t, the times of arrival of the first peaks on sensors 1 and 2 for events which occurred after 130,000 s were determined manually [13] and used to determine location. Examples of valley and peak waveforms are shown in Figure 6 with arrows indicating first peaks for sensors 1 and 2, top and bottom, respectively. Note that the first peak for the valley event on the top and bottom sensor is negative and the first peak for the peak event is positive; this is significant and is explained below.  