Birla Institute of Technology & Science, Pilani

**Distance Learning Programmes Division**

**Second Semester 2006-2007**

**Comprehensive Examination (EC-2 Regular)**

Course No. : ENGG ZC232

Course Title : ENGINEERING MATERIALS

Nature
of Exam : Open Book

Weightage :
60%

Duration : 3 Hours

Date
of Exam : 31/03/2007 (FN)

Note:

1.
Please follow all the *Instructions to Candidates* given on the
cover page of the answer book.

2.
All parts of a question should be answered consecutively. Each answer
should start from a fresh page.

3.
Mobile phones and computers of any kind should not be brought inside
the examination hall.

4.
Use of any unfair means will result in severe disciplinary action.

Q.1 (a) Indium has a tetragonal unit cell for which the ‘a’ and ‘c’ lattice parameters are 0.459 and 0.495 nm, respectively.

(i).
If the atomic packing factor and atomic radius are 0.693 and 0.1625 nm,
respectively, determine the number of atoms in each unit cell.

(ii).
The atomic weigh of indium is 114.82 g/mol; compute its theoretical
density.

[8]

Q.1 (b)
A cylindrical specimen of a titanium alloy having an elastic modulus of
107 GPa (15.5 x 10^{6} psi)
and an original diameter of 3.8 mm (0.15 in.) will experience only elastic
deformation when a tensile load of 2000 N (450 lb_{f})
is applied. Compute the maximum length of the specimen
before deformation if the maximum allowable elongation is 0.42 mm (0.0165 in.).
[5]

Q.2 (a)
A 50 wt% Ni-50 wt% Cu alloy is slowly cooled from 1400 ^{0}C
(2550 ^{0}F) to 1200^{0}C (2190 ^{0}F). [6]

(i).
At what temperature does the first solid phase form?

(ii).
What is the composition of this solid phase?

(iii).
What is the composition of this last remaining liquid phase?

Q.2 (b)
Show that the minimum cation-to-anion radius
for a coordination number of 6 is 0.414. [5]

Q.3 (a)
Explain why residual thermal stresses are introduced into a glass piece
when it is cooled.

(i).
Are thermal stresses introduced upon heating? Why or why not?

(ii).
How does the thickness of a glass ware affect the magnitude of the thermal stresses?
Why? [8]

Q.3 (b)
Compute the volume percent of graphite V_{Gr}
in a 3.5 wt% C cast iron, assuming that all the carbon exists as the graphite
phase. Assume densities of 7.9 and 2.3 g/cm^{3} for ferrite and
graphite, respectively. [6]

Q.4 (a)
The density and associated percent crystallinity
for two polypropylene materials are as follows:

__ρ(____g/cm ^{3}) Crystallinity
(%)__

0.904
62.8

0.895
54.4

(i).
Compute the densities of totally crystalline and totally amorphous
polypropylene.

(ii).
Determine the density of a specimen having 74.6 % crystallinity. [8]

Q.4 (b)
Briefly explain how each of the following influences the tensile or
yield strength of a semicrystalline polymer and why:

(a) Molecular weight (b) Degree of crystalline

(c) Deformation by
drawing (d) Annealing
of an undeformed material. [4]

Q.5 (a)
A continuous and aligned fibrous reinforced composite having a
cross-sectional area of 970 mm^{2} (1.5 in.^{2})
is subjected to an external tensile load. If the stresses sustained by the
fiber and matrix phases are 215 MPa (31,300 psi) and 5.38 MPa (780 psi), respectively, the force sustained by the fiber phase is 76,800 N (17,256 lb_{f}) and the total longitudinal composite strain
is 1.56 x 10^{-3}, then determine

(i). The force sustained by the
matrix phse

(ii). The modulus of elasticity of
the composite material in the longitudinal direction.

(iii). The moduli
of elasticity for fiber and matrix phases
[6]

Q.5 (b)
Suggest an appropriate material for each of the following applications,
and, if necessary, recommend corrosion prevention measures that should be
taken. Justify your suggestions.

(i).
Barrels to contain benzene.

(ii).
Pipe to transport hot alkaline (basic) solutions.

(iii).
Underground tanks to store large quantities of high-purity water.

(iv).
Laboratory bottles to contain relatively dilute solutions of nitric
acid. [4]

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