Page 44 - Analysis and Design of Machine Elements

Analysis and Design of Machine Elements
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Table 1.4 Selected conversion relationships.
Quantity ips to SI conversion Formula
Force 1 lb = 4.448 N 1 N = 1kgm s −2
Length 1 in. = 25.4 mm
Mass 1 lb = 0.454 kg
6
Modulus of elasticity 10 psi = 6.895 GPa
Moment or torque 1 lb in = 0.1138 N m
Power 1 hp = 550 lb ft s −1 = 745.7 W(watts) 1 W = 1J s −1 = 1N ms −1
Pressure 1 psi = 6895 Pa 1 Pa = 1N m −2
Stress 1 psi = 6.895 × 10 −3 MPa 1 Pa = 1Nm −2
Work or energy 1 lb in. = 0.1138 N m 1 J = 1Nm

system. If mass, length and time are base units, the system is an absolute system of units,
such as the International System of Units (SI) [8]. The unit system used in this book is SI.
In engineering design, any set of calculations must employ a consistent system of
units. Table 1.3 lists typical units associated with these systems and their standard
abbreviations.
Sometimes a unit has to be converted from one system to another. Their conversion
factorsare listed in Table1.4.

1.6 Standards and Codes

A standard is a set of specifications for elements, materials or processes formulated
through a cooperative effort among industrial organizations, with an aim to achieve
interchangeability, compatibility and uniformity for elements within a country or among
cooperating countries [5]. The adoption of standards ensures high design efficiency by
avoiding repetitive calculations, providing interchangeable elements on the spot with
minimum downtime [1]. It permits convenient manufacture with standard machines
and tooling.
Currently used standards are established by organizations or societies of various coun-
tries, such as the ANSI by the American National Standards Institute, BS by the British
Standards Institute, EN by the European Committee for Standardization, DIN by the
German Institute for Standardization, GB by the Standardization Administration of
the People’s Republic of China and ISO by the International Organization for Stan-
dardization. Other commonly used standards also include the AISI developed by the
American Iron and Steel Institute, ASME by the American Society of Mechanical Engi-
neers, ASTM by the American Society for Testing and Materials, SAE by the Society of
Automotive Engineers and so on.
A code is a set of specifications for analysis, design, manufacture and construction
[8]. Codes are legally binding documents, complied by a governmental agency, with an
aim to achieve a specified degree of safety, efficiency and performance or quality, and to
prevent damage, injury or loss of life [5, 8].