In a bathtub curve, what does the Y-axis typically represent?

In a bathtub curve, the Y-axis typically represents the failure rate. This graphical representation illustrates the life cycle of a product or system, showcasing the rate of failure over time. The curve is characterized by three distinct phases: the initial steep decline during the infant mortality phase, the flat middle section representing the steady state, and the eventual increase during the wear-out phase.

During the infant mortality phase, products may fail at a higher rate due to manufacturing defects or early-life issues. Once these initial failures are resolved, the failure rate becomes stable during the flat phase, where the reliability of the system is at its highest. Finally, as the product ages, wear and tear lead to an increased failure rate in the wear-out phase, reflecting the diminishing reliability.

Understanding the Y-axis as the failure rate is crucial for reliability engineers as it helps them analyze the reliability performance of systems over time and implement strategies to manage or mitigate failures. This insight supports informed decision-making in maintenance, design improvements, and resource allocation to enhance overall system reliability.