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Unformatted text preview: Sec_3.3.qxd 9/27/08 1:27 PM Page 253 253 SECTION 3.3 Circular Bars and Tubes Solution 3.3-2 Torsion of a drill bit
(b) RATE OF TWIST
From Eq. (3-14):
u d 4.0 mm T 0.3 N m G 75 GPa (a) MAXIMUM SHEAR STRESS u From Eq. (3-12):
tmax 16T u pd3 T
0.3 N # m
(75 GPa) a
b (4.0 mm)4
0.1592 rad/m 9.12°/m ; 16(0.3 N # m)
23.8 MPa ; Problem 3.3-3 While removing a wheel to change a tire,
a driver applies forces P 25 lb at the ends of two of the arms
of a lug wrench (see figure). The wrench is made of steel with
shear modulus of elasticity G 11.4 106 psi. Each arm of
the wrench is 9.0 in. long and has a solid circular cross section
of diameter d 0.5 in.
(a) Determine the maximum shear stress in the arm
that is turning the lug nut (arm A).
(b) Determine the angle of twist (in degrees)
of this same arm. P 9.0 in. A 9.0 in. d = 0.5 in.
P = 25 lb ...
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