They follow what is known in engineering and risk assessment circles as the bathtub curve
Burn-in testing (BIT) is supposed to detect and eliminate such "freaks," so that the final bathtub curve
of a product that underwent BIT does not contain the infant mortality portion.
A bathtub curve
is the corresponding cumulative distribution function (CDF) evaluated in two parts: one for the lower half of the PDF, integrated from left to right, and one for the upper half, integrated from right to left.
The failure rate is historically modelled (Crowe & Feinberg, 2001; Moubray, 1997; Andrews & Moss, 1993) using the traditional bathtub curve
shown in Figure 1.
Wg Cdr Bromehead, in evidence, said: "The bathtub curve
is a general engineering principle that is when something gets old, it is more likely to break.
A lot of facilities equipment has failure characteristics that are shaped in a pattern like a bathtub curve
(see Figure 1), meaning that it begins with a high incidence of failure (known as infant mortality); is followed by a lower, constant probability of failure; and is then followed by a wear-out zone where failure probability is high again.
With that in mind, the observed failure rate of the test population can be expressed on the Bathtub Curve
as the result of the composition of three prominent failure types: early life failure, constant (random) failure and wear-out failure.
The Q-Scale plot provides a visual representation of jitter breakdown, which is a more intuitive presentation of the nature of the jitter components than a traditional bathtub curve
If we experience a bathtub curve
, with a steep decline followed by a sustained period of low economic activity, then supply chain executives will face a challenge most have never faced before: how to manage supply chains in a no-growth or slow-growth economy efficiently and effectively.
Component failure rates have been shown to follow the traditional bathtub curve
[ILLUSTRATION FOR FIGURE 5 OMITTED] which depicts component life in three stages.