EAS107 Tensile tests were conducted on four cylindrical metallic specimens, A, B, C and D: introduction to engineering materials and Aeromaterials Assignment, SUSS, Singapore

Question 1a
Tensile tests were conducted on four cylindrical metallic specimens, A, B, C and D. The initial diameter of the specimens was measured to be 10.0 mm and the tensile test results is shown in Figure Q1a.

Interpret Figure Q1a to answer Q1a(i) to Q1a(v).

Question 1a(i)
Identify the specimen that is least tough. Justify your choice.
Question 1a(ii)
Calculate the ultimate tensile strength for specimen B.
Question 1a(iii)
Calculate the percentage reduction in area for specimen D if its cross sectional area after test was measured to be 50.5 mm2
.Question 1a(iv)
A force of 24 kN was applied to specimen A. State the elastic extension recorded and calculate its Young’s modulus in MPa.
Question 1a(v)
If cold working were to be performed on Specimen C, recommend an appropriate load to be applied. Justify your choice.

Question 1b
A steel sheet, 1.5 mm thick, has nitrogen atmosphere on both sides at 1200oC and is assumed to behave in accordance to Fick’s first law.
Question 1b(i)
Describe the assumption(s) for this steel sheet to behave in accordance to Fick’s first law.
Question 1b(ii)
The distance from the high-pressure surface and its concentration of nitrogen are measured for two positions in the steel sheet as listed in Table Q1b(ii).

Interpret the data in the table to calculate the concentration gradient of nitrogen in the steel sheet.

Question 1b(iii)
The diffusion coefficient for nitrogen in steel at 1200oC is 6 x 10-11 m 2 /s. Calculate its diffusion flux and state its units.
Question 1b(iv)
If the steel sheet in the above scenario is assumed to behave in accordance to Fick’s second law, is the assumption described in Question 1b(i) valid? Justify your answer.

Question 2a
List THREE (3) powder processing methods to shape ceramics powders into ‘green ceramics’.
Question 2b
Compare the properties of thermoplastics and ceramics as listed in Table Q2b. Copy Table Q2b and describe each property with one of the following: ‘higher’, ‘lower’ or ‘same’

Question 2c
Recall the repeating units of polyethylene and polystyrene and explain why polystyrene is stronger and stiffer than polyethylene.
Question 2d
Analyse the key differences between thermoplastics and thermosets based on the three perspectives listed in Table Q2d. Copy Table Q2d to answer the question.

Question 3a(i)
Calculate the critical radius for nickel using the data in Table Q3a(i).

Question 3a(ii)
Explain what will happen to a nickel nucleus of radius 2.50 x 10-10 cm present in the molten nickel.
Question 3a(iii)
If there is no undercooling due to slow cooling rate, recall an alternative foundry practice to refine the grain in the nickel casting during solidification.
Question 3b
Refer to Figure Q3b for Q3b(i) to Q3b(iv)

Question 3b(i)
Locate the eutectic point in the phase diagram. State the eutectic reaction and the temperature at which it occurs.
Question 3b(ii)
Apply the Lever rule to execute a calculation on the percentage of β phase present in the eutectic mixture. Show your working.
Question 3b(iii)
Describe the changes taking place as the alloy with 10%Sn is cooled slowly from 350°C to room temperature i.e. from Point 1 to Point 5 in the phase diagram.
Question 3c
With the aid of a schematic diagram to indicate the relationship between solubility of gas in metal with temperature, identify why it is important to remove the dissolved gas before solidification of the casting.

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