Final Exam 033

8/8/2019 Final Exam 033

http://slidepdf.com/reader/full/final-exam-033 1/12

KING FAHD UNIVERSITY OF PETROLEUM &

MINERALS, DHAHRAN, KSA

MECHANICAL ENGINEERING DEPARTMENT

ME 205 : MATERIAL SCIENCE

Summer semester 2003-04 (033)

Final ExamInstructor: Mr. M. Yaqub

Name____________________________Student #__________________________

Tuesday: August 17, 2004 Time Allowed: 2 hours

ME 205.01

Problem # Marks Grade

1 10

2 15

3 10

4 10

5 10

6 10

7 10

Total 75

Close books and handouts

Last page of the exam is a formula sheet

This exam contains twelve (12) pages including the cover page

8/8/2019 Final Exam 033


2

Problem # 1 10 points

Please tick the correct answer.

1. The figure shows a line defect in a crystal. This type of defect is called.

Edge dislocation

Mixed dislocation

Screw dislocation

Point defect

2. For this dislocation, dislocation line is

Inside the paper

Parallel to dislocation

Perpendicular to dislocation

Perpendicular to the paper

3. In inter-diffusion or impurity diffusion,

Atoms of the element forms a dislocation line

Atoms of same metal diffuses in the metal

Atoms of one metal diffuses in another metal

Atoms diffuses in another metal at constant rate

4. Percentage elongation is a measure of

Tensile strength

Toughness

Hardness

Ductility

5. In a slip system, normal to the slip plane and slip direction makes angles of 30

and 45 degree respectively, for this system

λ = 45 and φ = 30

λ = 30 and φ = 45

λ = 45 and φ = 45

λ = 30 and φ = 30

8/8/2019 Final Exam 033


3

6. Adding the impurity atom in pure metal

Decreases the yield strength of the metal

Increases the yield strength of the metal

Have no effect on properties of pure metal

Impurity atom can not add in pure metal

7. Isomorphous alloy systems are those in which

Alloy has more than two components

Two components of the alloy can only mix up to certain percentage

Two components of the alloy can mix in any composition

When alloy has two solid phases α and β

8. In non-equilibrium cooling of an isomorphous alloy

The composition of solid phase is non-uniform

The composition of solid phase is uniform

The composition of solid phase has a single component

The composition of solid phase is difficult to identify

9. In a lead-tin alloy system Eutectic α forms,

When solidification of the alloy starts

When half of the solidification is reached

When solidification comes to an end

None of above

10. In an Iron-Carbon alloy, the mass fraction of total ferrite is 0.93. Proeutectoid

phase for this alloy is

Ferrtire

Austinite

Cementite

Pearlite

8/8/2019 Final Exam 033


4


The wear resistance of a steel gear is to be improved by hardening its surface. This is

to be accomplished by increasing the carbon content within an outer surface layer as a

results of carbon diffusion into the steel; the carbon is to be supplied from an external

carbon-rich gaseous atmosphere at an elevated and constant temperature. The initial

carbon content of the steel is 0.2 wt %, whereas the surface concentration is to bemaintained at 1.00 wt %. For this treatment to be effective, a carbon content of 0.6 wt

% must be established at a position 0.75 mm below the surface. Specify the time

required for this diffusion process at temperature of 1000oC.

8/8/2019 Final Exam 033


5

Problem # 3 15 Points

Stress-Strain behavior for steel is given in the following graph. If the initial length and

diameter of the specimen is 50.8 and 12.8 mm respectively, find the following for the

steel.

8/8/2019 Final Exam 033


6

Continue Problem # 3

a) Tensile strength, fracture strength, and 0.2% yield strength.

b) Young’s modulus

c) Ductility in terms of percentage elongation and final length of the specimen.

d) True strain at necking point and necking diameter.

e) Modulus of resilience for the steel.

f) Strain hardening exponent for the steel.

8/8/2019 Final Exam 033


7

Problem # 4 10 Points

The average grain diameter for a brass material was measured as a function of time at

650oC, which is tabulated below at two different times:

a) What was the original grain diameter?

b) What grain diameter would you predict after 150 min at same temperature?

(Specify clearly any assumption you make to solve this problem)

Time

(min)

Grain Diameter

(mm)30 3.9 x 10

-2

90 6.6 x 10-2

8/8/2019 Final Exam 033


8


Following figure is the copper-nickel phase diagram. For the figure

1) Show the liquid, solid and liquid + solid region.

2) If an alloy of 50 wt % Ni – 50 wt % copper is cooled from 1400o

C, find

a) The temperature where solidification will start and the composition

of liquid and solid phase at this temperature.

b) The temperature where solidification will end and the composition

of liquid and solid phases at this temperature.

c) Weight fraction and compositions of liquid and solid phases

at temperature 1300oC

8/8/2019 Final Exam 033


9

Additional sheet for problem #5

8/8/2019 Final Exam 033


10


For a lead-tin alloy of composition 80 wt % Sn-20 wt % Pb and at 180oC, do the

following.

a) Determine the mass fraction and composition of α and β phase.

b) Determine the mass fraction of primary β and eutectic microconstituents after

solidification.

c) Determine the mass fraction of eutectic β .

8/8/2019 Final Exam 033


11


Consider 1.5 kg of austenite containing 1.15 wt % C, cooled to below 727oC.

a) What is the proeutectoid phase?

b) How many kg of each of total ferrite and cementite form?

c) How many kg each of pearlite and the proeutectoid phase form?

8/8/2019 Final Exam 033


12

)ln(2)1(ln 0

D

D

t =+= ε ε A

F

t =+= )1( ε σ σ

For grain Growth at constant temperature; t k d d n

o

n=−

Final Exam 033

Documents

Transcript of Final Exam 033