1
1.12 WEB REFERENCES
http://www.onlineconversion.com
Convert just about anything to anything else. Over 5,000 units, and 50,000 conversions.
http://www.katmarsoftware.com/uconeer.htm
Download a free units converter program for engineers.
Search a collection of technical standards with over 500,000 documents available for electronic download.
An online resource for finding companies and products manufactured in North America.
1.13 BIBLIOGRAPHY
For information on creativity and the design process, the following are recommended: J. L. Adams, The Care and Feeding of Ideas. 3rd ed. Addison Wesley: Reading, Mass., 1986.
J. L. Adams, Conceptual Blockbusting. 3rd ed. Addison Wesley: Reading, Mass., 1986.
J. R. M. Alger and C. V. Hays, Creative Synthesis in Design. Prentice-Hall: Englewood Cliffs, N.J., 1964.
M. S. Allen, Morphological Creativity. Prentice-Hall: Englewood Cliffs, N.J., 1962.
H. R. Buhl, Creative Engineering Design. Iowa State University Press: Ames, Iowa, 1960.
W. J. J. Gordon, Synectics. Harper and Row: New York, 1962.
J. W. Haefele, Creativity and Innovation. Reinhold: New York, 1962.
L. Harrisberger, Engineersmanship. 2nd ed. Brooks/Cole: Monterey, Calif., 1982.
D. A. Norman, The Psychology of Everyday Things. Basic Books: New York, 1986.
A. F. Osborne, Applied Imagination. Scribners: New York, 1963.
C. W. Taylor, Widening Horizons in Creativity. John Wiley: New York, 1964.
E. K. Von Fange, Professional Creativity. Prentice-Hall: Englewood Cliffs, N.J., 1959.
For information on writing engineering reports, the following are recommended: R. Barrass, Scientists Must Write. Chapman and Hall: New York, 1978.
W. G. Crouch and R. L. Zetler, A Guide to Technical Writing. 3rd ed. The Ronald Press Co.: New York, 1964.
D. S. Davis, Elements of Engineering Reports. Chemical Publishing Co.: New York, 1963.
D. E. Gray, So You Have to Write a Technical Report. Information Resources Press: Washington, D.C., 1970.
H. B. Michaelson, How to Write and Publish Engineering Papers and Reports. ISI: Philadelphia, Pa., 1982.
J. R. Nelson, Writing the Technical Report. 3rd ed. McGraw-Hill: New York, 1952.
28
MACHINE DESIGN -
An Integrated Approach
1
1.14 PROBLEMS
Table P1-0
Topic/Problem Matrix
1-1 It is often said, “Build a better mousetrap and the world will beat a path to your door. ” Consider this problem and write a goal statement and a set of at least 12 task 1.4 Engineering Model
specifications that you would apply to its solution. Then suggest 3 possible concepts to achieve the goal. Make annotated, freehand sketches of the concepts.
1-1, 1-2, 1-3
1.9 Units
1-2 A bowling machine is desired to allow quadriplegic youths, who can only move a joystick, to engage in the sport of bowling at a conventional bowling alley. Consider 1-4, 1-5, 1-6, 1-7, 1-8
the factors involved, write a goal statement, and develop a set of at least 12 task specifications that constrain this problem. Then suggest 3 possible concepts to achieve the goal. Make annotated, freehand sketches of the concepts.
1-3 A quadriplegic needs an automated page-turner to allow her to read books without assistance. Consider the factors involved, write a goal statement, and develop a set of at least 12 task specifications that constrain this problem. Then suggest 3
possible concepts to achieve the goal. Make annotated, freehand sketches of the concepts.
*1-4 Convert a mass of 1000 lbm to (a) lbf, (b) slugs, (c) blobs, (d) kg.
*1-5 A 250-lbm mass is accelerated at 40 in/sec2. Find the force in lb needed for this acceleration.
*1-6 Express a 100 kg mass in units of slugs, blobs, and lbm. How much does this mass weigh in lbf and in N?
1-7 Prepare an interactive computer program (using, for example, Excel, Mathcad, MATLAB, or TK Solver) from which the cross-sectional properties for the shapes shown on the inside front cover can be calculated. Arrange the program to deal with both ips and SI units systems and convert the results between those systems.
1-8 Prepare an interactive computer program (using, for example, Excel, Mathcad, MATLAB, or TK Solver) from which the mass properties for the solids shown on the page opposite the inside front cover can be calculated. Arrange the program to deal with both ips and SI units systems and convert the results between those systems.
1-9 Convert the program written for Problem 1-7 to have and use a set of functions or subroutines that can be called from within any program in that language to solve for the cross-sectional properties of the shapes shown on the inside front cover.
1-10 Convert the program written for Problem 1-8 to have and use a set of functions or
*
subroutines that can be called from within any program in that language to solve for Answers to these problems are
provided in Appendix D.
the mass properties for the solids shown on the page opposite the inside front cover.
2
MATERIALS AND
PROCESSES
There is no subject so old that something
new cannot be said about it.
Dostoevsky
2.0
INTRODUCTION
Whatever you design, you must make it out of some material and be able to manufacture it. A thorough understanding of material properties, treatments, and manufacturing processes is essential to good machine design. It is assumed that the reader has had a first course in material science. This chapter presents a brief review of some basic metallurgical concepts and a short summary of engineering material properties to serve as background for what follows. This is not intended as a substitute for a text on material science, and the reader is encouraged to review references such as those listed in the bibliography of this chapter for more detailed information. Later chapters of this text will explore some of the common material-failure modes in more detail.
Table 2-0 shows the variables used in this chapter and references the equations, figures, or sections in which they are used. At the end of the chapter, a summary section is provided which groups the significant equations from this chapter for easy reference and identifies the chapter section in which they are discussed.
2.1
MATERIAL-PROPERTY DEFINITIONS
Mechanical properties of a material are generally determined through destructive testing of samples under controlled loading conditions. The test loadings do not accurately duplicate actual service loadings experienced by machine parts except in certain special cases. Also, there is no guarantee that the particular piece of material you purchase for your part will exhibit the same strength properties as the samples of similar materials tested previously. There will be some statistical variation in the strength of any par-29
30
MACHINE DESIGN -
An Integrated Approach
Table 2-0
Variables Used in This Chapter
Symbol
Variable
ips units
SI units
See
2
A
area
in2
m2
Sect. 2.1
A 0
original area, test specimen
in2
m2
Eq. 2.1 a
E
Young's modulus
psi
Pa
Eq. 2.2
el
elastic limit
psi
Pa
Figure 2-2
f
fracture point
none
none
Figure 2-2
G
shear modulus, modulus of rigidity
psi
Pa
Eq. 2.4
HB
Brinell hardness
none
none
Eq. 2.10
HRB
Rockwell B hardness
none
none
Sect. 2.4
HRC
Rockwell C hardness
none
none
Sect. 2.4
HV
Vickers hardness
none
none
Sect. 2.4
J
polar second moment of area
in4
m4
Eq. 2.5
K
stress intensity
kpsi-in0.5
MPa-m0.5
Sect. 2.1
Kc
fracture toughness
kpsi-in0.5
MPa-m0.5
Sect. 2.1
l 0
gage length, test specimen
in
m
Eq. 2.3
N
number of cycles
none
none
Figure 2-10
P
force or load
lb
N
Sect. 2.1
pl
proportional limit
psi
Pa
Figure 2-2
r
radius
in
m
Eq. 2.5 a
Sd
standard deviation
any
any
Eq. 2.9
Se
endurance limit
psi
Pa
Figure 2-10
Sel
strength at elastic limit
psi
Pa
Eq. 2.7
Sf
fatigue strength
psi
Pa
Figure 2-10
Sus
ultimate shear strength
psi
Pa
Eq. 2.5
Sut
ultimate tensile strength
psi
Pa
Figure 2-2
Sy
tensile yield strength
psi
Pa
Figure 2-2
Sys
shear yield strength
psi
Pa
Eq. 2.5c
T
torque
lb-in
N-m
Sect. 2.1
UR
modulus of resilience
psi
Pa
Eq. 2.7
UT
modulus of toughness
psi
Pa
Eq. 2.8
y
yield point
none
none
Figure 2-2
strain
none
none
Eq. 2.1 b
tensile stress
psi
Pa
Sect. 2.1
shear stress
psi
Pa
Eq. 2.3
angular deflection
rad
rad
Eq. 2.3
arithmetic mean value
any
any
Eq. 2.9 b
Poisson's ratio
none
none
Eq. 2.4
ticular sample compared to the average tested properties for that material. For this reason, many of the published strength data are given as minimum values. It is with these caveats that we must view all published material-property data, as it is the engineer’s responsibility to ensure the safety of his or her design.