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A new product is required to demonstrate 99% reliability at 1.5 million cycles with 80%
confidence. Given a Weibull shape parameter of 2.8, how long must 8 units be tested
to demonstrate the required reliability assuming no failures?
Solution
 Select "Testing" from the menu, and the following screen appears.
 Enter the shape parameter of 2.8, a sample size of 8, a confidence level of 0.8,
reliability of 0.99 and a time of 1.5. Click the "Test Duration" radio
button, and the test duration will be computed. To demonstrate 99% reliability with
80% confidence at 1.5 million cycles requires testing 8 units for 4 million cycles with no
failures. This is shown in the figure below.
 Change the Test Duration to 1.5, and click the "Sample Size" radio button.
To demonstrate 99% reliability with 80% confidence at 1.5 million cycles requires
testing 161 units for 1.5 million cycles with no failures. By testing a sample size
of 8 for 4 million cycles ( a total of 32 million test cycles) instead of
161 samples for
1.5 million cycles ( a total of 241.5 million test cycles), the total number of test cycles
is reduces by 80%. If the shape parameter is greater than 1, the total number of
test cycles decreases as the test duration increases.
