In reliability engineering, what does the typical product reliability life cycle (the classic “bathtub curve”) indicate about failure rates over time?

Introduction / Context:
Reliability engineers commonly model failure behavior with the bathtub curve. This conceptual model shows how the failure rate of many products changes throughout their lifespan, informing warranty policies, maintenance schedules, and design-for-reliability strategies. Understanding the pattern is foundational in electronics, mechanical systems, and safety-critical industries.

Given Data / Assumptions:

• We consider a typical population of units under normal conditions.
• Failure rate refers to the rate parameter over time, not a single probability.
• Environmental conditions and usage can alter parameters, but the canonical pattern persists.

Concept / Approach:
The classic bathtub curve has three phases: (1) early failures (infant mortality) where failure rate decreases as weak units fail; (2) useful life with an approximately constant failure rate; and (3) wear-out period where failure rate increases due to aging, fatigue, or material degradation. This model helps plan burn-in, preventive maintenance, and end-of-life replacement.

Step-by-Step Solution:

Verification / Alternative check:
Empirical field data for electronics and mechanical parts often fit this three-phase pattern, though exact shapes vary with design quality and environment.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming constant failure rate across all life phases; ignoring environment-induced acceleration that shifts the curve.

Final Answer:
It has three distinct rates of failure over its life.