TABLE OF CONTENTS Three life periods may be detected generally for most components and products: (1) early life, (2) useful life, and (3) wear-out life. During early life two types of failures may occur: (1) early failures and (2) chance failures. The early failures may be caused by poor manufacturing techniques, poor workmanship, poor quality control: insufficient burning in, debugging, and breaking in; etc. The chance failures may be caused by the interference or overlap of the designed in strength and the experienced stress during operation, due to insufficient design safety factors or margins, occurrence of higher than expected random loads, occurrence of lower than expected random strengths, etc.
The useful life period is characterized by the occurrence of chance failures only, which yield the lowest failure rate in the life of the component or product.
The wear-out life period is characterized by the occurrence of two types of failures: (1) chance failures and (2) wear-out failures. The wear-out type of failure may be caused by aging, degradation, wear, creep, fatigue, short designed in life, and poor service, maintenance, repair, and replacement practices.
In this chapter the times-to-failure distributions best suited to describe early failures alone, chance failures alone, and wear-out failures alone will be presented, and techniques for determining their distribution function, reliability function, conditional reliability function, and the failure rate function will be developed.
It was stated previously that early failures are the result of the production of weak or substandard components. These...
