Characteristics of the Weibull Distribution
In the last several issues of Reliability HotWire, we looked at how distributions are defined and how common reliability metrics are derived. In this issue, we will take a closer look at a specific distribution that is widely used in life data analysis - the Weibull distribution. Named for its inventor, Waloddi Weibull, this distribution is widely used in reliability engineering and elsewhere due to its versatility and relative simplicity. 

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• Introduction to Accelerated Testing Types - For a variety of reasons, manufacturers may wish to obtain reliability test results more quickly than they can when the data comes from products operating under normal use conditions. They may use accelerated life tests to capture life data for the product under accelerated stress conditions, which cause the units to fail more quickly. Performed correctly, accelerated testing can significantly reduce test times, resulting in reduced time to market, lower product development costs and lower warranty costs, as well as other benefits. See http://www.ReliaSoft.com/newsletter/4q2001/accel_tests.htm.
• Limitations of the Exponential Distribution for Reliability Analysis - The unsupported assumption that most reliability engineering problems can be modeled well by the exponential distribution is still widely held. In a quest for simplicity and solutions that we can grasp, derive and easily communicate, many practitioners have embraced simple equations derived from the underlying assumption of an exponential distribution for reliability prediction, accelerated testing, reliability growth, maintainability and system reliability analyses. However, the situations in which the exponential distribution may be appropriately applied are not as common as some would have you believe. See http://www.ReliaSoft.com/newsletter/4q2001/exponential.htm.