The Bathtub Curve
The bathtub curve is an equipment failure-rate curve with an initial sharply declining failure rate, followed by a prolonged constant-average failure rate, after which the failure rate again increases sharply. Bathtub Curve shows the lifetime of the population of the products through graphical representation. Bathtub contains three contents or periods: Infant Mortality, Normal Life and End of Life Wear-Out. When all of these periods combine, it creates the product failure. Below is the diagram of Bathtub Curve. There are three components of the Bathtub Curve. The first stage of Bathtub Curve is Early Life which is also called Infant Mortality Failure. Early Life is the phase where there is decreasing failure rate. In this stage, usually product failure occurs not because of the usages but rather of lack of proper manufacturing process, defect products or designs and lack of quality control. Similarly, the second period is Useful Life or Normal Life in which the product has comparatively steady failure rate. Usually in this stage product failure occurs due to normal wear and tears and random defects, stress of the product. As shown in the figure, Useful life is longer and stable other two stages indicated by two lines on the left and right lines. Third stage is wear-out period where the failure rate is high because of the excess use of the product leading to wear out of critical parts of the product for example breaking Vacuum rubber or oil reduction in car. In order to make the product run through its intended life cycle, manufacturer must make sure that the resources or materials he uses are adequate in quality.
In the case scenario 2, the automakers have extended the warranty at wear-tear period of the product life cycle. I think the automakers have extended their warranty from three year to seven to ten years because of the facts that as