Name ___________________________

MAE 454 – Machine Design and Manufacturing

Exam 2

November 12, 2012 The exam is closed notes and book. Calculators are not permitted nor are any other electronic

devices; cell phones, iPods, etc. must be removed from the desk. The exam is worth 100 points;

individual problems are worth the points indicated. Place your answer for the multiple choice

questions next to the problem number in the space provided. Note that Problems 9 and 28

are worth 31% of the exam grade.

1. There are five major design considerations for shafts. List three of these five considerations (6

Points)

a) Material, layout/geometry, stress, deflection, critical speed/resonance.

b) Also acceptable Component connection/couplings, limits and fits.

c)

2. What is the difference between a shaft and an axle? (2 Points)

An axle is a non-rotating member that carries no torque and is used to support other

components. A shaft is a rotating member used to transmit power.

3. What is an approximate value for the maximum allowable transverse deflection for spur

gears in shaft design? (2 Points)

a) < 0.0001 in.

b) <0.001 in.

c) <0.01 in.

d) <0.1 in.

4. What is an approximate value for allowable shaft slope for spherical ball bearings in

shaft design? (2 Points)

a) < 0.005 rad.

b) <0.05 rad.

c) <0.5 rad.

d) <5.0 rad.

5. What type of screw thread is found in passenger vehicle scissor jacks in the US? (2 Points)

A power or lead screw with ACME or square threads.

See Chapter 7

Pg. 360

Pg. 379

C

B

Pg. 379

Name ___________________________

P

P

6. For a threaded (nut and bolt) connection, there are five different stresses examined. List three

of these five stresses. Use words and not schematics for your answer and provide where

each stress acts. (6 Points)

a) Torsional shear stress main body of screw.

Axial compression stress (buckling too) main body of screw.

b) Thread bearing stress thread to bolt surface interface.

Thread bending stress thread root diameter.

c) Thread shear stress thread root diameter.

7. In practice, how is a bolt’s preload actually set? (2 Points)

A torque wrench is used.

8. In bolted connections, what level (as a fraction of proof load (Fp)) of preload (Fi) should be

applied for the following two different applications: (2 Points)

a) Fi = * Fp (non permanent connections, reused fasteners)

b) Fi = * Fp (permanent connections)

9. The bracket shown is bolted to a column with an

external load P acting at the right pin joint. (i) Draw

a free body diagram of the bracket. (ii) What type

of stress(es) act on the bracket? (iii) What type of

stress(es) act on the bolts at the bracket location?

(12 Points)

(i)

(Note: R=1/2P)

(ii) Bearing at force P hole and at both bolt holes locations. Axial tension in bar. Shear tear out.

(iii) Bearing at both bolts. Transverse shear at both bolts. May also have axial tension if there is

a preload applied.

Pg. 417

Pg. 442

0.75

0.90

P

R R

Name ___________________________

10. What were the three different types of welding techniques discussed in class? (3 Points)

a) Arc

b) TIG

c) MIG

11. What is the approximate maximum single pass weld thickness that can be applied in

practice as discussed in class? (2 Points)

a) <0.005 in.

b) <0.01 in.

c) <0.1 in.

d) <0.5 in.

e) No limit.

12. Provide the welding symbol that would be

used on a technical drawing for the

hollow tube welded to the flat plate with

a 5 mm weld shown. (2 Points)

13. For the horizontal bar welded to the vertical

member shown, draw and label the type of

stress(es) acting on the critical point(s) for the

weld. (4 Points)

14. In a helical coil compression spring, where does the spring generally fail? Provide a written

response and not a graphical image. (2 Points)

In the main body of the spring (due to combined torsional and transverse shear).

d

Pg. 518

Name ___________________________

15. Provide a common, every-day application where a helical coil compression spring is used. (2

Points)

Many are possible.

16. Identify the type of bearing in the figure. (2 Points)

Straight roller or needle roller.

17. What type of rolling contact bearing can take radial and significant thrust loads? (2 Points)

Tapered roller.

18. How is failure defined for rolling contact bearings? (2 Points)

Spalling or pitting area.

19. For rolling contact bearings with combined radial and thrust loads, how is the equivalent

radial load determined? Provide a short description of the general procedure. (4 Points)

The equivalent load is determined by comparing the axial load to the radial load. If the

ratio is above a defined value (e), then the axial load is combined with the radial load using

weighting factors for the effect of the radial load and the effect of the axial load. These

weighting factors depend on the ratio of the axial load to the maximum static axial load.

20. In the analysis of journal bearings, what differentiates hydrodynamic lubrication analysis

from boundary-lubrication analysis? (2 Points)

The difference between these two analyses is based upon the relative film thickness. If

there is insufficient film thickness such that there is asperity-to-asperity contact then a boundary

lubrication analysis is performed. If there is sufficient film thickness, then a hydrodynamic

analysis is performed.

Pg. 572

Pg. 573

Pg. 579

Name ___________________________

21. In boundary-lubricated bearings, there were four different operating limits to selecting the

bearing. List three of the four types of limits. (6 Points)

a) Maximum Pressure, Maximum Velocity, Maximum Pressure*Velocity, and Temperature

b)

c)

22. In the design of a journal bearing, what is the range of length-to-diameter ratio that is

suggested to be used? (2 Points)

≤ L/D ≤

23. List two advantages of plain (journal) bearings over roller element bearings. (2 Points)

a) Lower cost, smaller diameter, higher speed, …

b)

24. List two advantages of roller element bearings over plain (journal) bearings. (2 Points)

a) Manufacturer interchangeability, narrower width, better stop/start life, noise indicates

failure, …

b)

25. What is the typical efficiency range of a bevel gear mesh during power transmission? (2

Points)

a) ~20 to 90%

b) ~90 to 95%

c) ~95 to 98%

d) ~98 to 99%

e) 100%

26. Provide an advantage of a helical gear over a spur gear. (2 Points)

Larger power transmission, lower noise, …

27. What type(s) of gear(s) can provide intersecting shafts? (2 Points)

Bevel

c or d

1/2 2

Pg. 661

Pg. 664

Name ___________________________

28. For the gear train shown below, shaft a is rotating at 1000 rpm with a

torque of 100 in-lb. Determine (a) the output speed at shaft c, (b) the

output torque at shaft c, and (c) the center-to-center distance between

shafts a and c. The efficiency of each gear mesh is 98% and the

gear pitch is 10 teeth/in. (19 Points)