Product Life Cycle Curve Or Bath Tub Curve
Why the Emphasis on Reliability?
The Consumer Protection Act of 1972 marked a critical turning point in product safety. In 1972, Congress determined that “an unacceptable number of consumer products” presented unreasonable risks of injury to the consumer. This act, along with other government legislative actions, has raised the level of awareness of both manufacturers and consumers in matters related to product performance.
Products as we know them have become increasingly complicated over the years. Manufacturers are racing to add more features and more components. The probability of product failure increases as the number of features increases. Manufacturers are increasingly aware of the challenge of increasing the reliability of their products to match the additional features. In the age of automation, manufacturers grapple with how to design automated products that are still operable manually even when the automatic component fails.
Increased competition has created a barrage of competing products. Product reliability has become a competitive weapon in the battle for market share. Today, many manufacturers have made the goal of increased product reliability part of their strategic plan. History has shown us that when a company consistently produces unreliable products, it would not survive.
Product Life Cycle Curve
Most products go through three distinct phases from inception to wearout. Figure depicts a typical product life cycle curve. The curve,
Product Life Cycle Curve
sometimes referred to as “bathtub” curve, shows a plot of the failure rate λ as a function of time. It consists of the debugging phase, the chancefailure phase, and the wear-out phase.
The debugging phase, which is also called infant-mortality phase, is characterized by a time in the life of the product when there is a drop in the failure rate as early failures are identified and worked out, particularly during prototype testing or pre-shipment testing. During this phase, the curve is exponential. Some of the early failures are due to any number of factors including inadequate materials, incorrect installation, or errors in the manufacturing process.
The chance-failure phase occurs between time t1 and t2, at a constant rate. Failure during this phase occurs randomly, and may be due to misapplication or misuse. The assumption of a constant failure rate is valid for most products; however, some products may have a failure rate that increases with time. The final phase of the cycle is the wear-out phase, and is characterized by a rise in the failure rate that occurs as the product ages and wears out. Normal wear could result in misalignment, loose fittings, and component interference, and could lead to an increase in the failure rate.
Before we introduce the components of reliability, let us first understand the causes of unreliability.
Or in Other Words
DEFINITION
Reliability is the probability that a device will perform its intended function satisfactory without failure, for the stated period of time, under the specified operating conditions. In the above definition, there are 4 factors which are essential to the concept of reliability.
(a) It is a probability.
(b) It is associated with time.
(c) Satisfactory performance is required.
(d) Operating environment should be defined.