Describe the typical phases of failure rate over a product's life (the bathtub curve).

• A. Early-life (infant) failures with decreasing hazard, a middle 'useful life' with roughly constant hazard, and wear-out failures with increasing hazard.
• B. Early-life (infant) failures with increasing hazard, a middle 'useful life' with roughly constant hazard, and wear-out failures with decreasing hazard.
• C. Hazard remains constant throughout life.
• D. Early-life failures with constant hazard, middle-life decreasing hazard, wear-out with constant hazard.

Answer: (A)

The typical failure-rate pattern over a product’s life is a bathtub curve: high at the start, dipping to a relatively constant level in the middle, and rising again as the product ages. Early-life failures are common because manufacturing defects, assembly issues, or latent flaws cause many units to fail soon after deployment; over time, those defective items are removed from the population, so the hazard decreases. In the middle period, the surviving population experiences failures mostly due to random, wear-insensitive causes, so the failure rate stays roughly constant. As the product wears out, aging, fatigue, and cumulative wear push the hazard upward again, leading to more failures in the final phase.

This view aligns with real-world testing and reliability data, and it explains why designs and maintenance strategies often focus on reducing early-life defects, monitoring performance during the useful life, and planning end-of-life replacements as wear-out approaches. Other patterns—such as a hazard that stays constant for all life or one that increases earlier or decreases later—don’t reflect how defects, random failures, and aging typically interact over time.