Bathtub curve

Definition

The bathtub curve is a graphical representation that illustrates the failure rates of a product over time, characterized by three distinct phases: early failures, a period of normal life, and wear-out failures. This curve helps in understanding the reliability of a system or component, showing how failure rates change as a product ages. The name comes from its shape, which resembles a bathtub, indicating low failure rates after the initial phase and increasing rates as the product approaches the end of its useful life.

5 Must Know Facts For Your Next Test

1. The bathtub curve has three segments: infant mortality (early failures), normal life (constant failure rate), and wear-out period (increasing failure rate).
2. The initial phase shows a high failure rate due to manufacturing defects or early-life failures, which tend to decrease as these units fail.
3. The middle section represents the normal operational phase where the failure rate stabilizes and remains relatively constant.
4. The wear-out phase indicates that as products age, they experience an increasing rate of failure due to wear and tear or obsolescence.
5. Understanding the bathtub curve is crucial for designing maintenance schedules and improving product reliability over its life cycle.

Review Questions

• How does the bathtub curve illustrate the relationship between time and failure rates in product reliability?
  • The bathtub curve visually represents how failure rates change over a product's lifecycle. In the early stage, known as infant mortality, there is a high failure rate due to defects, which decreases as those faulty units are eliminated. The curve then levels off during the normal operational phase where the failure rate stabilizes, before rising again in the wear-out phase when components begin to fail due to aging and deterioration.
• What implications does understanding the bathtub curve have for maintenance strategies in engineering?
  • Recognizing the phases of the bathtub curve allows engineers and maintenance teams to develop effective maintenance strategies. Early in the product's life, proactive measures can address infant mortality issues, while during normal life, routine maintenance can help sustain performance. As the wear-out phase approaches, more frequent inspections and potential replacements can minimize downtime and reduce costs associated with unexpected failures.
• Evaluate how the bathtub curve can inform decisions related to product design and longevity in engineering practices.
  • The bathtub curve provides valuable insights for engineers when designing products with longevity in mind. By understanding that products will face varying failure rates throughout their lifecycle, engineers can incorporate robust materials and manufacturing processes to minimize early failures. Additionally, design considerations such as modularity can facilitate easier repairs or upgrades during the normal life phase, while also planning for obsolescence in the wear-out phase can ensure a smoother transition to newer technologies without significant disruptions.

Related terms

Reliability Function: A function that provides the probability that a system or component will perform its intended function without failure for a specified period.

Mean Time Between Failures (MTBF): A measure used to predict the average time between failures of a system or component during its operational life.

Failure Rate:

The frequency with which an engineered system or component fails, typically expressed as failures per unit of time.