1.6. RELIABILITY HISTORY 13
reliability in engineering design was initiated and established by the AGREE report [10] in
1957. e method of reliability in engineering has become extremely important. e importance
of reliability in engineering design can be expressed and explained through the following four
aspects.
• Reliability in engineering design is a more scientific and advanced relative measure of the
status of a component, device, or system. In reality, all design parameters such as ma-
terial strength, working load, and component geometric dimensions have some inherent
uncertainty. Per the definition of reliability, reliability considers all these uncertainties of
design parameters in engineering design and systematically links them together through a
probability theory to conduct engineering design.
• Reliability in engineering design is a more practical measure of the status of a component,
device, or system because it admits that any designed component could fail no matter how
we design it. e reliability R is designed into the components per design specification, is
an attribute of the component, and can be used to predict the percentage of failure of the
designed component. e percentage of failure of the component will be equal to .1 R/.
• Reliability is directly and tightly related to the reputation of a company and a product. In
today’s competitive market, every device and system is expected to perform satisfactorily
throughout its expected life span. Usually, the value of reliability is proportional to the
price of the product. e higher reliability the product has, the higher the cost needed to
manufacture it. Product with higher reliability might affect company markets. However,
the lower the reliability of the product indicates a higher percentage of failure. Although
the manufacturer gives a warranty to cover the failures of the product during its early stages
of life, too many failures during the warranty period not only cause inconvenience to the
customer and high cost of repair to the manufacturer but also mean a loss of reputation
and market share.
• Reliability in engineering design is a systematic tool for designing a complicated product
or system with the required reliability. Generally, no device or system will perform reliably
unless it is designed specifically for reliability. e complicated system typically includes
many subsystems, and each subsystem can have thousands of components. Reliability in
engineering design intends to design the reliability into each component or to predict the
percentage failure of each component. e proper arrangement or allocation of reliability
into each component can design each subsystem with the required reliability.
1.6 RELIABILITY HISTORY
Reliability in engineering design is an application of probability theory. Ancient mathematicians
such as Italian mathematician Gerolamo Cardano in the 16th century, and French mathemati-
cians Pierre de Fermat and Blaise Pascal in the 17th century, studied and researched probability
14 1. INTRODUCTION TO RELIABILITY IN MECHANICAL DESIGN
theory, which was mainly about gambling. However, the reliability in engineering emerged as
a separate discipline in the 1950s due to the extensive research and study on military electronic
equipment.
During World War II, Germans applied basic reliability concepts to improve the reliabil-
ity of their V1 and V2 rockets [3]. e following are some unbelievable facts about electronic
equipment during World War II [3].
• During 1941–1945, 60–75% of vacuum tubes in communication equipment failed.
• During 1941–1945, nearly 60% of the airborne equipment shipped to the Far East was
damaged on arrival.
• During 1941–1945, nearly 50% of the spare parts and equipment in storage became un-
serviceable before they were ever used.
• In 1947, nearly 70% of the electronic equipment possessed by the Navy was not operating
properly.
Such extremely high percentages of electronic equipment failures, in reality, resulted in
great attention and extensive research activities in the United States. In 1950, the Air Force
formed the ad hoc Group on Reliability of Electronic Equipment to study the situation and
recommend measures that could increase the reliability of equipment. In 1951, the Navy began
an extensive and lengthy study on vacuum tubes. In 1951, the Army started a similar investi-
gation. Due to such an extensive study, in 1952, the Department of Defense established the
Advisory Group on Reliability of Electronic Equipment (AGREE) to coordinate the research
activities of the Air Force, Navy, and Army. In June 1957, AGREE published its first report:
“Reliability of Military Electronic Equipment” [10]. Two of their many conclusions and rec-
ommendations in the AGREE report were: (1) reliability testing must be made an integral part
in the development of a new system and (2) procuring agencies should accept the equipment
only after getting the reliability demonstrated by a manufacturer. It is widely accepted that this
AGREE first report in 1957 is the foundation of the reliability in engineering design.
e extensive research on the reliability of electronic equipment in the 1950s formed the
first set of reliability-related standards. Some examples of these military standards are listed in
the following.
• In 1952, the AGREE established a military standard MIL-STD-781 “Reliability Quali-
fication and Production Approval Test,” which was revised as MIL-STD-781b in 1967.
• In 1955, the AGREE established military standards MIL-STD-441 “Reliability of Mil-
itary Electronic Equipment.”
• In 1961, MIL-STD-756 for reporting prediction of weapons’ system reliability.
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