Usually, the concept of constant failure rate (i.e., exponentially distributed times to failure) is used to evaluate the reliability of electronic components. This concept may or may not be applicable to mechanical parts. The history of mechanical reliability may be traced back to World War II and the development of V1 and V2 rockets in Germany. However, it was not until the mid-1960s when mechanical reliability received serious attention because of the loss of two spacecrafts (i.e., Syncom I and Mariner III) because of mechanical failures . Consequently, the National Aeronautics and Space Administration (NASA) initiated many projects to improve reliability of mechanical items.