the two data curves on the figure illustrate that

They are caused by defects designed into orīuilt into a product. They cause 'dead-on-arrival' products and undermine customer confidence. Infant Mortality What Causes It and What to Do About It?įrom a customer satisfaction viewpoint, infant mortalities are unacceptable. And we don't want any wear-out failures to occur during the expected useful lifetime of the product. Because these failures may incur warranty expense or create service support costs, we want the bottom of the bathtub to be as Relatively constant rate when measured over a long period of time.

Theoretically, the failures during normal life occur at random but with a Significant number of failures occur in a short time, causing early customer dissatisfaction and warranty expense. The infant mortality period is a time when the failure rate is dropping, but is undesirable because a

We are interested in the characteristics illustrated by the entire bathtub curve. It is a period when the failure rate is increasing, and has been observed in products after just a few months of use. Conversely, wear-out will not always happen Infant mortality is the time over which the failure rate of a product is decreasing, and may last for years. Infant mortality does not mean 'products that fail within 90 days' orĪny other defined time period. It is rare to have enough short-term and long-term failure information to actually model a population of products with a calibrated bathtub curve.Īlso note that the actual time periods for these three characteristic failure distributions can vary greatly. Note that the bathtub curve is typically used as a visual model to illustrate the three key periods of product failure and not calibrated to depict a graph of the expected behavior for a A product manufacturer must assure that all specified materials are adequate to function through the intended product life. A product's useful life is limited by its shortest-livedĬomponent. Wear-out is a fact of life due to fatigue or depletion of materials (such as lubrication depletion in bearings). Normal life failuresĪre normally considered to be random cases of 'stress exceeding strength.' However, as we'll see, many failures often considered normal life failures are actually infant mortalityįailures. Units will fail relatively early (infant mortality failures), others (we hope most) will last until wear-out, and some will fail during the relatively long period typically called normal life.įailures during infant mortality are highly undesirable and are always caused by defects and blunders: material defects, design blunders, errors in assembly, etc. The bathtub curve, displayed in Figure 1 above, does not depict the failure rate of a single item, but describes the relative failure rate of an entire population of products over time. The bathtub curve: normal life failures and end of life wear-out. Part Two (presented in next month's HotWire) will address the remaining two periods of (presented in this issue) introduces the bathtub curve and covers infant mortality and burn-in. The material will be presented in two parts. Rate by screening out infant mortality failures. It describes methods to reduce failures at each stage of product life and shows how burn-in, when appropriate, can significantly reduce operational failure This article provides an overview of how infant mortality, normal life failures and wear-out modes combine to create the overall product failure distributions. Rate followed by a normal life period (also known as 'useful life') with a low, relatively constant failure rate and concluding with a wear-out period that exhibits an increasing failure rate. The bathtub curve consists of three periods: an infant mortality period with a decreasing failure Reliability specialists often describe the lifetime of a population of products using a graphical representation called the bathtub curve.

This paper is adapted with permission from work done while at Hewlett-Packard. Retired Hewlett-Packard Senior Reliability Specialist, currently a ReliaSoft Reliability Field Consultant Part One - The Bathtub Curve, Infant Mortality and Burn-in The Bathtub Curve and Product Failure Behavior

The two data curves on the figure illustrate that