Page 37 - Shigley's Mechanical Engineering Design

bud29281_ch01_002-030.qxd 11/11/2009 5:35 pm Page 12 pinnacle s-171:Desktop Folder:Temp Work:Don't Delete (Jobs):MHDQ196/Budynas:

12 Mechanical Engineering Design
1–6 Standards and Codes

A standard is a set of specifications for parts, materials, or processes intended to
achieve uniformity, efficiency, and a specified quality. One of the important purposes
of a standard is to limit the multitude of variations that can arise from the arbitrary cre-
ation of a part, material, or process.
A code is a set of specifications for the analysis, design, manufacture, and con-
struction of something. The purpose of a code is to achieve a specified degree of safety,
efficiency, and performance or quality. It is important to observe that safety codes do
not imply absolute safety. In fact, absolute safety is impossible to obtain. Sometimes
the unexpected event really does happen. Designing a building to withstand a 120 mi/h
wind does not mean that the designers think a 140 mi/h wind is impossible; it simply
means that they think it is highly improbable.
All of the organizations and societies listed below have established specifications
for standards and safety or design codes. The name of the organization provides a clue
to the nature of the standard or code. Some of the standards and codes, as well as
addresses, can be obtained in most technical libraries or on the Internet. The organiza-
tions of interest to mechanical engineers are:
Aluminum Association (AA)
American Bearing Manufacturers Association (ABMA)
American Gear Manufacturers Association (AGMA)
American Institute of Steel Construction (AISC)
American Iron and Steel Institute (AISI)
American National Standards Institute (ANSI)
American Society of Heating, Refrigerating and Air-Conditioning Engineers
(ASHRAE)
American Society of Mechanical Engineers (ASME)
American Society of Testing and Materials (ASTM)
American Welding Society (AWS)
ASM International
British Standards Institution (BSI)
Industrial Fasteners Institute (IFI)
Institute of Transportation Engineers (ITE)
Institution of Mechanical Engineers (IMechE)
International Bureau of Weights and Measures (BIPM)
International Federation of Robotics (IFR)
International Standards Organization (ISO)
National Association of Power Engineers (NAPE)
National Institute for Standards and Technology (NIST)
Society of Automotive Engineers (SAE)

1–7 Economics

The consideration of cost plays such an important role in the design decision process
that we could easily spend as much time in studying the cost factor as in the study of
the entire subject of design. Here we introduce only a few general concepts and sim-
ple rules.
First, observe that nothing can be said in an absolute sense concerning costs.
Materials and labor usually show an increasing cost from year to year. But the costs