Examples provided here are purely for illustrating software features and functionality.

Weibull++ Example 3 – Analyzing Sudden Death Data

Download Example File for Version 10 (*.rsgz10) or Version 9 (*.rsr9)

Background

The reliability requirement for a new roller assembly is a reliability of 95% for 50,000 cycles at a 70% lower one-sided confidence level. The objective is to demonstrate this reliability goal through testing. The test lab at the manufacturing facility can test only 5 units at a time, so a test is set up for a sample size of 20 components (4 groups of 5 units each), to be run sequentially until the first failure in each group. In other words, the first group of 5 units is tested until one of the 5 units fails. After that, the second group is tested until the first failure and so forth.

Experiment and Data

The following data are recorded during the experiment:

Analysis Discussion

Even though the test is performed sequentially, the analysis can include all data as follows:

Analysis

Step 1: Using Weibull++, the first step is to create a new standard folio for grouped times-to-failure (in cycles) with suspensions data.

Figure 1: Data Sheet Setup window.

Step 2: The next step is to enter the life data from the test in the second table above. The data set is then analyzed using the 2-parameter Weibull distribution and MLE. The results are shown next.

Figure 2: Standard folio with data and results.

Step 3: The remaining task is to determine the demonstrated reliability at 50,000 cycles and at a 70% confidence level. The QCP in Weibull++ is used to compute this value, as shown next. In this case, the demonstrated reliability at the desired confidence level is found to be 96.41%, which is greater than the requirement, thus demonstrating the requirement.

Alternatively, a probability plot can be obtained, which shows the same result. This is shown next. Note that range of the x-axis scale has been changed to 45,000 – 70,000.

Supplemental Discussion