Wear-Out

A graph of the hazard rate versus time that describes the typical life cycle of a population of items, characterized by three distinct phases: (1) Infant Mortality — a decreasing failure rate period caused by manufacturing defects, installation errors, or design weaknesses; (2) Useful Life — a period of approximately constant, low failure rate representing random failures; (3) Wear-Out — an increasing failure rate period caused by age-related degradation mechanisms.

The early-life period of a component or system characterized by a higher-than-normal failure rate that decreases over time (Weibull beta < 1). Infant mortality failures are caused by latent defects introduced during manufacturing, installation, or commissioning — they are not age-related degradation but rather quality problems that manifest early. Common causes include material defects, welding flaws, installation errors, contamination, and incorrect settings.

A failure that occurs with approximately constant probability per unit time, independent of the item's age or accumulated operating time (Weibull beta approximately 1). Random failures are caused by unpredictable combinations of stress and strength, external events, or operating conditions that cannot be anticipated by age-based inspection or maintenance. They are equally likely to occur at any point during the useful life period.

The Weibull shape parameter (beta, also written as b or k) that determines the form of the failure distribution and the nature of the failure rate over time. Beta < 1 indicates decreasing failure rate (infant mortality); beta = 1 indicates constant failure rate (random failures, equivalent to exponential distribution); beta > 1 indicates increasing failure rate (wear-out). The value of beta reveals the physics of the dominant failure mechanism.

The time by which a specified percentage of a population is expected to have failed, derived from the Weibull distribution parameters. B10 life is the time by which 10% of the population has failed (90% survival); B50 is median life (50% survival); B90 is the time by which 90% have failed. B-life values are used to set preventive replacement intervals and warranty periods.

Maintenance performed at predetermined intervals or according to prescribed criteria to reduce the probability of failure or functional degradation. Preventive maintenance includes time-based activities (replacement, overhaul, calibration at fixed intervals), usage-based activities (at fixed operating hours or cycles), and condition-based activities (when monitored parameters indicate intervention is needed). The goal is to prevent failures that would otherwise occur.