MECH325 - Homework Hints, Answers, and Extra Requirements

Homework 7 (Chapters 9 and 10)

TO ENHANCE YOUR LEARNING, PLEASE TRY TO WORK THE PROBLEMS FIRST WITHOUT LOOKING AT THE HINTS AND ANSWERS BELOW.

MAKE SURE YOU SATISFY ALL REQUIREMENTS LISTED BELOW AND IN THE ORIGINAL PROBLEM STATEMENTS (UNLESS INDICATED OTHERWISE BELOW).

NOTE - BECAUSE MOST ANSWERS ARE PROVIDED, IT IS VERY IMPORTANT THAT YOU SHOW ALL STEPS IN YOUR WORK.  THE GRADING WILL BE BASED ON THE COMPLETENESS, CLARITY, AND CORRECTNESS OF YOUR WORK, NOT JUST THE ANSWERS YOU PROVIDE.

9.21
[10 pts]
  • Δ = 1.25 x 10-11
  • po = 336 MPa
9.23
[20 pts]
  • Δ = 1.11 x 10-11
  • diam = 8.4 mm
10.5
[20 pts]
  • (a)  d = 1.125 in
  • (b)  Traise = 2070 in-lb
  • (c)  min coef friction required = 0.08
10.6
[25 pts]
  • Do not neglect collar friction.
  • (a)  p = 0.2 in,  L = 0.4 in,  depth = 0.1 in,  dm = 0.9 in,  λ = 8.05 deg
  • (b)  assume starting friction is 1/3 higher than running friction
    • Traise = 2810 in-lb
    • Tlower = 1490 in-lb
  • (c) efficiency = 28%
10.20
[10 pts]
  • (a)  min preload = 6860 lb
  • (b)  plate force = 1640 lb
10.41
[15 pts]
  • (a)  use SF=20 or above (justify this choice based on Section 6.12, impact considerations, and safety concerns)
    • thread choice: M36X4
  • (b)  balance the bolt tensile strength and the thread stripping strength
    • t = 33.8 mm
    • number of threads required = 9