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Metal 259 - Fall-1998 - Exam 3

Par time - 17.5 min. (Time required to read questions, think a little, and write answers)

Only answers placed in the space provided will be considered.

Diagrams and drawings, where appropriate, are welcome.

1. (0) Put your social security no. on the line above now.

2. (6) One of the objectives in the design of and materials selection for bicycles is light weight. Choose three of the candidate materials for bicycle frames discussed in class, discuss briefly one or two key attributes (properties) which are considered in the choice of materials for lightweight frames (write about the role of these factors in the design process). 2 min.

3. (10) Draw a cross-section of the structure of a weldment in a chrome-moly bicycle frame. Name the various regions and describe the microstructure in these regions by giving the phases and/or constituents present. Tell why these constituents are present. Use a simple configuration like that shown below; the cross-section of the walls of two tubes are welded together in the middle are to be shown. 2 min.

4. (6) Two ways in which sensitization in stainless steels can be defeated are (explain why they work): 1.5 min.

5. (12) List four types of "micro" corrosion cells ("macro" cells, such as those involving dissimilar metals, non-homogeneous stress distribution, concentrations, active/passive metals, etc., don't qualify). Describe an example of each. Drawings helpful. 3.5 min.

6. (10) List two positives and two negatives in the use of Ti and its alloys. 0.5 min.

Positives:

Negatives:

7. (10) Below are listed the design criteria for a precision spur gear. 5 min.

Precision spur gear - 6" diam., 1" face

Must: no scoring, low wear, cyclic loading
from rest to 3000 rpm every 3 min.,
low tooth load (<50 lb)

Nice: high finish attainable by grinding, high
precision shape

Quantity: 2 sets

Delivery: 6 months max.

Life: 4 hrs./day for 5 years

Expected cost: $300 each

a. Choose four materials from different classes in the list below which are possible candidates for this gear.

b. List four general areas for consideration in choosing which of your four materials would be the best one for the gear.

c. Now make a choice and give an extensive discussion on the bases of how you made it.

8. (12) For each of the four examples of different corrosion cells listed below, describe a different method for the suppression of the corrosion. Tell what part of the galvanic cell is removed by each method. Use a completely different method of suppressing corrosion for each example. There are frequently some tradeoffs involved in suppressing corrosion; discuss where appropriate. Drawings helpful. 3 min.

a. Soldered Cu tubing joints in a plumbing installation. Pb-Sn solder was used. (Dissimilar metals cell)