17_ch 07 Mechanical Design budynas_SM_ch07

# 17_ch 07 Mechanical Design budynas_SM_ch07 -...

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194 Solutions Manual • Instructor’s Solution Manual to Accompany Mechanical Engineering Design From Figs. 6-20 and 6-21, q = 0 . 75 and q s = 0 . 92 , K f = 1 + 0 . 75(1 . 9 1) = 1 . 68, and K fs = 1 + 0 . 92(1 . 32 1) = 1 . 29 . From Eq. (7-11), with M m = T a = 0, 1 n = 16 π (0 . 04) 3 ± 4 ² 1 . 68(326 . 67) 174(10 6 ) ³ 2 + 3 ² 1 . 29(107) 390(10 6 ) ³ 2 ´ 1 / 2 n = 1 . 98 At x = 330 mm: The von Mises stress is the highest but it comes from the steady torque only. D / d = 30 / 20 = 1 . 5, r / d = 2 / 20 = 0 . 1 K ts = 1 . 42, q s = 0 . 92 K fs = 1 . 39 1 n = 16 π (0 . 02) 3 ( 3 ) ² 1 . 39(107) 390(10 6 ) ³ n = 2 . 38 Check the other locations. If worse-case is at x = 210 mm, the changes discussed for the slope criterion will im- prove the strength issue. 7-11 and 7-12 With these design tasks each student will travel different paths and almost all details will differ. The important points are • The student gets a blank piece of paper, a statement of function, and some constraints–explicit and implied. At this point in the course, this is a good experience.
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