Page 95 - Shigley's Mechanical Engineering Design

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70 Mechanical Engineering Design
Choose which tests you would actually perform, and in what sequence, to minimize time and
cost, but to determine the material with a reasonable level of confidence. The table below pro-
vides results that would be available to you if you choose to perform a given test. Explain your
process, and include any calculations. You may assume the material is one listed in Table A–5. If
it is carbon steel, try to determine an approximate specification from Table A–20.

Test Results if test were made
Prob. 2–21 Prob. 2–22 Prob. 2–23
(a) Dark gray, rough surface Silvery gray, smooth surface Reddish-brown, tarnished,
finish, moderate scale finish, slightly tarnished smooth surface finish
(b) Metallic gray, moderate Silvery gray, deep scratch Shiny brassy color, deep
scratch scratch
(c) Magnetic Not magnetic Not magnetic
(d) W = 7.95 lbf W = 2.90 lbf W = 9.00 lbf
(e) d = 5 16 in d = 7 8 in d = 17 32 in
(f) H B = 200 H B = 95 H B = 70

2–24 Search the website noted in Sec. 2–20 (http://composite.about.com/cs/software/) and report your
findings. Your instructor may wish to elaborate on the level of this report. The website contains a
large variety of resources. The activity for this problem can be divided among the class.
2–25 Research the material Inconel, briefly described in Table A–5. Compare it to various carbon and
alloy steels in stiffness, strength, ductility, and toughness. What makes this material so special?
2–26 Consider a rod transmitting a tensile force. The following materials are being considered: tung-
sten carbide, high-carbon heat-treated steel, polycarbonate polymer, aluminum alloy. Using the
Ashby charts, recommend one or two of the materials for a design situation in which failure is by
exceeding the strength of the material, and it is desired to minimize the weight.
2–27 Repeat Prob. 2–26, except that the design situation is failure by excessive deflection, and it is
desired to minimize the weight.
2–28 Consider a cantilever beam that is loaded with a transverse force at its tip. The following materials
are being considered: tungsten carbide, high-carbon heat-treated steel, polycarbonate polymer,
aluminum alloy. Using the Ashby charts, recommend one or two of the materials for a design
situation in which failure is by exceeding the strength of the material and it is desired to minimize
the weight.
2–29 Repeat Prob. 2–28, except that the design situation is failure by excessive deflection, and it is
desired to minimize the weight.
2–30 For an axially loaded rod, prove that b = 1 for the E r guidelines in Fig. 2–16.
b
2–31 For an axially loaded rod, prove that b = 1 for the S r guidelines in Fig. 2–19.
b
2–32 For a cantilever beam loaded in bending, prove that b = 1 2 for the E r guidelines in Fig. 2–16.
b
2–33 For a cantilever beam loaded in bending, prove that b = 2 3 for the S r guidelines in Fig. 2–19.
b
2–34 Consider a tie rod transmitting a tensile force F. The corresponding tensile stress is given by
σ = F/A, where A is the area of the cross section. The deflection of the rod is given by Eq. (4–3),
which is δ = (Fl)/(AE), where l is the length of the rod. Using the Ashby charts of Figs. 2–16
and 2–19, explore what ductile materials are best suited for a light, stiff, and strong tie rod.
Hint: Consider stiffness and strength separately.