y-intercept was forced to zero. The resulting slope was 3.6 mm2/sec (R2 = 0.92, 95%
confidence interval = 3.35 to 3.85).
600
y = 4.3301x 52.193
SR 2 = 0.9696 *
C5400 -
300
'200 .
100
0
0 50 100 150
t1/2 (sec)
Figure 6-46. Plot of defect circumference C x depth D vs. tl/2 for all heating methods
(air-filled defects with ATmax > 2.00C)
A similar analysis was performed for the epoxy-filled defects in Series A. The plot
of C x d vs. tl/2 is provided in Figure 6-47. Only defects with ATmax greater than 2.0C
were considered in the analysis. Since ATmax values for epoxy-filled defects tend to be
lower than air-filled defects, the sample size for this analysis was limited to 9
observations. The slope determined by the linear regression analysis was 1.81 mm2/sec
(R2 = 0.99, 95% confidence interval = 1.64 to 1.99).
The physical explanation for why epoxy-filled defects have a longer half-life than
air-filled defects was not found in the literature. A possible explanation is that epoxy-
filled defects store more energy and hence the defect material maintains a higher
temperature for longer periods of time than the air-filled defects. Under this scenario, the
heated epoxy acts like a heat source after the heat stored in the material above the defect
drains away to the perimeter.