failure rate curve

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Failure rate curveclick for a larger image
Fig. 40 Failure rate curve. Graph showing a typical curve.

failure rate curve

or

‘bath tub curve’

or

Weibull analysis

a curve which reflects the RELIABILITY of a component of a product or machine, measured in terms of the proportion of a sample of that component which fails at different phases of its operational life. Fig. 40 shows a typical failure rate curve for a sample of the component which is divided into three phases:
  1. the ‘infant’ or burn-in period of the component is characterized by an initial high rate of failure. The early failure rate then decreases rapidly as surviving components prove themselves to be reliable;
  2. the adult or normal useful life period of the component is typified by a low and relatively constant rate of component failure;
  3. the ageing or wear-out period of the component is characterized by a rise in the failure rate as the component reaches the end of its designed life.

Each of these phases will reflect the adequacy of the design of the component, the quality of the materials used to make it, and the consistency with which it is manufactured.

In designing finished products, firms may seek to reduce the extent of early failure of components by laboratory testing of new product designs, and by using feedback from consumer panels and test marketing to perfect the design of the product. In determining GUARANTEE or WARRANTY periods for products, firms need to be aware of when the components of the product are likely to reach the end of their normal useful life and begin to experience rising failure rates. Failure rate profiles for components of factory machines can likewise be employed to plan the firm's MAINTENANCE and machine replacement programmes. See QUALITY CONTROL.

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