TABLE OF CONTENTS A number of failure distribution models are available. Among these are the exponential, gamma, pareto, Weibull, normal or Gaussian, lognormal, Birbaum-Saunders, inverse Gaussian, and extreme value distributions. Further details about these distributions are available in Hoyland and Rausand[3] or other texts on reliability theory.
Weibull [5] published a generalized equation to describe lifetime distributions in 1951. The two-parameter version of the Weibull equation is simpler and is suitable for many applications. The three-parameter version of the equation is suitable for situations where there is a clear threshold period before commencement of deterioration. By selecting suitable values of these parameters, the equation can represent a number of different failure distributions. Readers can refer to Davidson[6] for details on the actual procedure to follow in doing the analysis.
The Weibull distribution is of special interest because it is very flexible and seems to describe many physical failure modes. It lends itself to graphical analysis, and the data required is usually available in most history records. We can obtain the survival probability at different ages directly from the analysis chart. We can also use software to analyze the data. Figure 3.15 shows a Weibull plot made using a commercial software application.
It is fairly easy to gather data required to carry out Weibull analysis, since time-to-failure and preventive replacement details for the failure mode are nearly all that we need. For this we need a record of the date and description of...
