Failure Times - Duane Example

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This example appears in the Reliability Growth and Repairable System Analysis Reference book.

A prototype of a system was tested with design changes incorporated during the test. A total of 12 failures occurred. The data set is given in the following table.

Developmental Test Data

Failure Number	Cumulative Test Time(hours)
1	80
2	175
3	265
4	400
5	590
6	1100
7	1650
8	2010
9	2400
10	3380
11	5100
12	6400

1. Estimate the Duane parameters.
2. Plot the cumulative and instantaneous MTBF curves.
3. How many cumulative test and development hours are required to meet an instantaneous MTBF goal #of 500 hours?
4. How many cumulative test and development hours are required to meet a cumulative MTBF goal of 500 hours?

Solution

1. The next figure shows the data entered into RGA along with the estimated Duane parameters.

Entered data and the estimated Duane parameters.

2. The following figure shows the cumulative and instantaneous MTBF curves.

The cumulative and instantaneous MTBF curves.

3. The next figure shows the cumulative test and development hours needed for an instantaneous MTBF goal of 500 hours.

Required test time for an instantaneous MTBF of 500 hours.

4. The figure below shows the cumulative test and development hours needed for a cumulative MTBF goal of 500 hours.

Required test time for a cumulative MTBF of 500 hours.