Page 272 - Handbook of Materials Failure Analysis

268 CHAPTER 11 The reliability design of mechanical system

Existing products New products Rival products
AB series PA series C series

Compare Compare

Expected problem Comparative advantage for
Existing product
(15 items) for new design performance and reliability
(10 items) (10 items)

Total 35 items

Performance Reliability
(15 items) (20 items)

Usual Special
performance performance Reliability marginal Reliability quantitative
specifications specifications test specifications test specifications
RM (15 items) RQ (5 items)
UP (10 items) SP (5 items)
FIGURE 11.7
Complete testing sets of verification specifications for quality assurance.

time, it is a reliability issue; if not, it is a performance issue. The specifications are
further divided into four categories: usual performance (UP) specifications, special
performance (SP) specifications, reliability marginal (RM) test specifications, and
reliability quantitative (RQ) test specifications.
UPs check the expected performance by the usual operator or consumer. SPs
check performance under extraordinary environments, such as tropical heat or ele-
vated electromagnetic fields. RMs are used for identifying physical changes under
severe or peculiar conditions, including unusual usage environments like electro-
static overstress or lightning surges. Finally, RQs are for reviewing the product state
under normal conditions and for estimating the product lifetime, the BX life (lifetime
of the cumulative failure rate X%), and the annual failure rate within lifetime. Note
that the lifetime index MTTF refers to the time-point at which about 60% of the pro-
duction lot fails, which is an unacceptable rate.

5 CASE STUDY OF VERIFICATION SPECIFICATION: ROBOTICS
The purpose of this classification is to assign appropriate specialists to check whether
requisite specifications have been evaluated sufficiently. Consider the format for
Robot A in Table 11.1. Each line in the table represents one specification, which
should be recorded. Specialists can browse the list, reviewing brief summaries for
the adequacy of the verification specifications.