Page 16 - Marks Calculation for Machine Design

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PREFACE
maximum-normal-stresstheory,themaximum-shear-stresstheory,andthedistortion-energy
theory are presented with examples. Similarly, for brittle materials, the maximum-normal-
stress theory, the Coulomb-Mohr theory, and the modified Coulomb-Mohr theory are pre-
sented with examples. The discussion on stress concentration factors provides how to use the
stress-concentration factors found in Marks’ Standard Handbook for Mechanical Engineers
and other references. In the discussion on column buckling, the Euler formula is presented
for long slender columns, the parabolic formula for intermediate length columns, the secant
formula for eccentric loading, as well as a discussion on how to deal with short columns.
Chapter 7, Fatigue and Dynamic Design, contains information on how to design for
dynamic conditions, or fatigue. Fatigue associated with reversed loading, fluctuating load-
ing, and combined loading is discussed with numerous examples. The Marin equation is
provided with examples on the influence of its many modifying factors that contribute to
establishing an endurance limit, which in turn is used to decide whether a design is safe.
Extensive use of the Goodman diagram as a graphical approach to determine the safety of
a design is presented with appropriate examples.
Beginning Part 2, Chapter 8, Machine Assembly, discusses the two most common ways
of joining machine elements: bolted connections and welded connections. For bolted con-
nections, the design of the fastener, the members, calculation of the bolt preload in light of
the bolt strength and the external load, static loading, and fatigue loading are presented with
numerous examples. For welded connections, both butt and fillet welds, axial, transverse,
torsional, and bending loading is discussed, along with the effects of dynamic loading, or
fatigue, in shear.
Chapter 9, Machine Energy, considers two of the most common machine elements
associated with the energy of a mechanical system: springs and flywheels. The extensive
discussion on springs is limited to helical springs, however these are the most common
type used. Additional spring types will be presented in future editions. In the discussion
on flywheels, two system types are presented: internal combustion engines where torque is
a function of angular position, and electric motor driven punch presses where torque is a
function of angular velocity.
Chapter 10, Machine Motion, covers the typical machine elements that move: linkages,
gears, wheels and pulleys. The section on linkages includes the three most famous designs:
the four-bar linkage, the quick-return linkage, and the slider-crank linkage. Extensive calcu-
lations of velocity and acceleration for the slider-crank linkage are presented with examples.
Gears, whether spur, helical, or herringbone, are usually assembled into gear trains, of which
there are two general types: spur and planetary. Spur gear trains involve two or more fixed
parallel axles. The relationship between the speeds of these gear trains, based on the num-
ber of gear teeth in contact, is presented with examples. Planetary gear trains, where one
or more planet gears rotate about a single sun gear, are noted for their compactness. The
relative speeds between the various elements of this type of design are presented.
While much has been presented in these ten chapters, some topics had to be left out
to meet the schedule, not unlike the choices and tradeoffs that are part of the day-to-day
practice of engineering. If there are topics the reader would like to see covered in the second
edition, the author would very much like to know. Though much effort has been spent in
trying to make this edition error free, there are inevitably still some that remain. Again, the
author would appreciate knowing where these appear.
Good luck on your designs. It has been a pleasure uncovering the mystery of the prin-
ciples and formulas in machine design that are so important to bringing about a safe and
operationally sound design. It is hoped that the material in this book will inspire and give
confidence to your designs. There is no greater reward to a machine designer than to know
they have done their best, incorporating the best practices of their profession. And remem-
ber the first rule of machine design as told to me by my first supervisor, “when in doubt,
make it stout!”