Page 94 - Shigley's Mechanical Engineering Design

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Materials 69
2–13 A gray cast iron part has a Brinell hardness number of H B = 200. Estimate the ultimate strength
of the part in kpsi. Make a reasonable assessment of the likely grade of cast iron by comparing
both hardness and strength to material options in Table A–24.
2–14 A part made from 1040 hot-rolled steel is to be heat treated to increase its strength to approxi-
mately 100 kpsi. What Brinell hardness number should be expected from the heat-treated part?
2–15 Brinell hardness tests were made on a random sample of 10 steel parts during processing. The
results were H B values of 230, 232(2), 234, 235(3), 236(2), and 239. Estimate the mean and
standard deviation of the ultimate strength in kpsi.
2–16 Repeat Prob. 2–15 assuming the material to be cast iron.
2–17 For the material in Prob. 2–6: (a) Determine the modulus of resilience, and (b) Estimate the mod-
ulus of toughness, assuming that the last data point corresponds to fracture.
2–18 Some commonly used plain carbon steels are AISI 1010, 1018, and 1040. Research these steels
and provide a comparative summary of their characteristics, focusing on aspects that make each
one unique for certain types of application. Product application guides provided on the Internet
by steel manufacturers and distributors are one source of information.
2–19 Repeat Prob. 2–18 for the commonly used alloy steels, AISI 4130 and 4340.
2–20 An application requires the support of an axial load of 100 kips with a round rod without exceed-
ing the yield strength of the material. Assume the current cost per pound for round stock is given
in the table below for several materials that are being considered. Material properties are avail-
able in Tables A–5, A–20, A–21, and A–24. Select one of the materials for each of the following
additional design goals.
(a) Minimize diameter.
(b) Minimize weight.
(c) Minimize cost.
(d) Minimize axial deflection.

Material Cost/lbf
1020 HR $0.27
1020 CD $0.30
1040 Q&T @800°F $0.35
4140 Q&T @800°F $0.80
Wrought Al 2024 T3 $1.10
Titanium alloy (Ti-6Al-4V) $7.00

2–21 to A 1-in-diameter rod, 3 ft long, of unknown material is found in a machine shop. A variety of
2–23 inexpensive nondestructive tests are readily available to help determine the material, as described
below:
(a) Visual inspection.
(b) Scratch test: Scratch the surface with a file; observe color of underlying material and depth
of scratch.
(c) Check if it is attracted to a magnet.
(d) Measure weight (±0.05 lbf ).
(e) Inexpensive bending deflection test: Clamp one end in a vise, leaving 24 in cantilevered.
Apply a force of 100 lbf (±1 lbf). Measure deflection of the free end (within ±1 32 in).
( f) Brinell hardness test.