Example 5

Life Data Analysis

Maintenance Optimization

Engineered Software Home Page

Nine samples were tested for 3 million cycles without failure, and 1 sample survived 2.84 million cycles before failing.  Given a Weibull shape parameter of 3.8, what is the lower 95% confidence limit for reliability at 2 million cycles?  What is the lower 95% confidence limit for the time to fail when the reliability is 99%?

Solution

1. Enter the data into the individual data entry grid as shown below.
   
   
   
2. Select "Weibull" then   "Bayesian Estimation" from the "Parameter Estimation" menu.
3. Enter the shape parameter of 3.8, the confidence level of 0.95, and click the "Compute" button.
4. In the text box to the right of "Time" enter 2.
5. In the text box to the right of "Reliability" enter 0.99.
6. The 95% lower confidence limit for reliability at 2 million cycles is 0.9016.  The lower 95% confidence limit for the time to fail when the reliability is 99% is 1.082 million cycles.  This is shown in the figure below.