Budynas ch07

# Shigley's Mechanical Engineering Design (McGraw-Hill Series in Mechanical Engineering)

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Chapter 7 7-1 (a) DE-Gerber, Eq. (7-10): A = ± 4[2 . 2(600)] 2 + 3[1 . 8(400)] 2 ² 1 / 2 = 2920 lbf · in B = ± 4[2 . 2(500)] 2 + 3[1 . 8(300)] 2 ² 1 / 2 = 2391 lbf · in d = 8(2)(2920) π (30 000) 1 + ³ 1 + ´ 2(2391)(30 000) 2920(100 000) µ 2 1 / 2 1 / 3 = 1 . 016 in Ans . (b) DE-elliptic, Eq. (7-12) can be shown to be d = ³ 16 n π · A 2 S 2 e + B 2 S 2 y 1 / 3 = 16(2) π · ¸ 2920 30 000 ¹ 2 + ¸ 2391 80 000 ¹ 2 1 / 3 = 1 . 012 in Ans. (c) DE-Soderberg, Eq. (7-14) can be shown to be d = ´ 16 n π ¸ A S e + B S y ¹µ 1 / 3 = ´ 16(2) π ¸ 2920 30 000 + 2391 80 000 ¹µ 1 / 3 = 1 . 090 in Ans. (d) DE-Goodman: Eq. (7-8) can be shown to be d = ´ 16 n π ¸ A S e + B S ut ¹µ 1 / 3 = ´ 16(2) π ¸ 2920 30 000 + 2391 100 000 ¹µ 1 / 3 = 1 . 073 in Ans. Criterion d (in) Compared to DE-Gerber DE-Gerber 1.016 DE-elliptic 1.012 0.4% lower less conservative DE-Soderberg 1.090 7.3% higher more conservative DE-Goodman 1.073 5.6% higher more conservative

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Chapter 7 179 7-2 This problem has to be done by successive trials, since S e is a function of shaft size. The material is SAE 2340 for which S ut = 1226 MPa, S y = 1130 MPa, and H B 368 . Eq. (6-19): k a = 4 . 51(1226) 0 . 265 = 0 . 685 Trial #1 : Choose d r = 22 mm Eq. (6-20): k b = ± 22 7 . 62 ² 0 . 107 = 0 . 893 Eq. (6-18): S e = 0 . 685(0 . 893)(0 . 5)(1226) = 375 MPa d r = d 2 r = 0 . 75 D 2 D / 20 = 0 . 65 D D = d r 0 . 65 = 22 0 . 65 = 33 . 8mm r = D 20 = 33 . 8 20 = 1 . 69 mm Fig. A-15-14: d = d r + 2 r = 22 + 2(1 . 69) = 25 . 4mm d d r = 25 . 4 22 = 1 . 15 r d r = 1 . 69 22 = 0 . 077 K t = 1 . 9 Fig. A-15-15: K ts = 1 . 5 Fig. 6-20: r = 1 . 69 mm, q = 0 . 90 Fig. 6-21: r = 1 . 69 mm, q s = 0 . 97 Eq. (6-32): K f = 1 + 0 . 90(1 . 9 1) = 1 . 81 K fs = 1 + 0 . 97(1 . 5 1) = 1 . 49 We select the DE-ASME Elliptic failure criteria. Eq. (7-12) with d as d r , and M m = T a = 0, d r = 16(2 . 5) π ³ 4 ± 1 . 81(70)(10 3 ) 375 ² 2 + 3 ± 1 . 49(45)(10 3 ) 1130 ² 2 ´ 1 / 2 1 / 3 = 20 . 6mm
180 Solutions Manual • Instructor’s Solution Manual to Accompany Mechanical Engineering Design Trial #2 : Choose d r = 20 . 6mm k b = ± 20 . 6 7 . 62 ² 0 . 107 = 0 . 899 S e = 0 . 685(0 . 899)(0 . 5)(1226) = 377 . 5MPa D = d r 0 . 65 = 20 . 6 0 . 65 = 31 . 7mm r = D 20 = 31 . 7 20 = 1 . 59 mm Figs. A-15-14 and A-15-15: d = d r + 2 r = 20 . 6 + 2(1 . 59) = 23 . 8mm d d r = 23 . 8 20 . 6 = 1 . 16 r d r = 1 . 59 20 . 6 = 0 . 077 We are at the limit of readability of the ﬁgures so K t = 1 . 9, K ts = 1 . 5 q = 0 . 9, q s = 0 . 97 K f = 1 . 81 K fs = 1 . 49 Using Eq. (7-12) produces d r = 20 . 5mm . Further iteration produces no change. Decisions : d r = 20 . D = 20 . 5 0 . 65 = 31 . , d = 0 . 75(31 . 5) = 23 . Use D = 32 mm, d = 24 mm, r = 1 . Ans. 7-3 F cos 20°( d / 2) = T , F = 2 T / ( d cos 20°) = 2(3000) / (6 cos 20°) = 1064 lbf M C = 1064(4) = 4257 lbf · in For sharp ﬁllet radii at the shoulders, from Table 7-1, K t = 2 . 7, and K = 2 . 2 . Examining Figs. 6-20 and 6-21, with S ut = 80 kpsi, conservatively estimate q = 0 . 8 and q s = 0 . 9 . These estimates can be checked once a speciﬁc ﬁllet radius is determined. Eq. (6-32): K f = 1 + (0 . 8)(2 . 7 1) = 2 . 4 K = 1 + . 9)(2 . 2 1) = 2 . 1 (a) Static analysis using fatigue stress concentration factors: From Eq. (7-15) with M = M m , T = T m , and M a = T a = 0, σ ± max = ³ ± 32 K f M π d 3 ² 2 + 3 ± 16 K T π d 3 ² 2 ´ 1 / 2

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Chapter 7 181 Eq. (7-16): n = S y σ ± max = S y ± ² 32 K f M π d 3 ³ 2 + 3 ² 16 K fs T π d 3 ³ 2 ´ 1 / 2 Solving for d , d = µ 16 n π S y 4( K f M ) 2 + 3( K T ) 2 · 1 / 2 ¸ 1 / 3 = µ 16(2 . 5) π (60 000) 4(2 . 4)(4257) 2 + 3(2 . 1)(3000) 2 · 1 / 2 ¸ 1 / 3 = 1 . 700 in Ans .
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## This document was uploaded on 01/24/2008.

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Budynas ch07 - Chapter 7 7-1 (a) DE-Gerber, Eq. (7-10): A =...

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