Читать книгу Reliability Analysis, Safety Assessment and Optimization - Enrico Zio - Страница 19

Reliability of an item can be defined as the complement to its probability of failure, which can be estimated statistically on the basis of the number of failed items in a sample. Suppose that the sample size of the item being tested or monitored is n0. All items in the sample are identical, and subjected to the same environmental and operational conditions. The number of failed items is n_f and the number of the survived ones is n_s, which satisfies

(1.1)

The percentage of the failed items in the tested sample is taken as an estimate of the unreliability, ,

(1.2)

Complementarily, the estimate of the reliability, R^(t), of the item is given by the percentage of survived components in the sample:

(1.3)

Example 1.1

A valve fabrication plant has an average output of 2,000 parts per day. Five hundred valves are tested during a reliability test. The reliability test is held monthly. During the past three years, 3,000 valves have failed during the reliability test. What is the reliability of the valve produced in this plant according to the test conducted?

Solution

The total number of valves tested in the past three years is

The number of failed components is

According to Equation 1.3, an estimate of the valve reliability is