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Tec 111:Introduction To Material Science Question Paper
Tec 111:Introduction To Material Science
Course:Bachelor Of Electrical And Electronics Engineering
Institution: Moi University question papers
Exam Year:2012
COURSE CODE: TEC 111
COURSE TITLE: INTRODUCTION TO MATERIAL SCIENCE
FIRST SEMESTER 2011/2012
Answer all five questions. All questions carry equal marks
Question one
a. Give two reasons why it is important for an engineering student to study material science and engineering course. (2mks)
b. Calculate the number of atoms in 1 cubic mm of copper given that the relative density of copper is 8.96 and its atomic mass is 63.546 (Avogadro’s number = 6.02232x10^23 atoms/mole)
c. Give the reason why Chromium (Cr) 24 and Copper (Cu) 29 have irregularities during the filling of the 3d shell in the periodic table of elements. (2mks)
d. Briefly discuss Rutherford experiment, 1911, which explains the structure of atoms. (4mks)
e. When is the greatest reinforcing effect and maximum strength obtained in a fiber reinforced composite material (2mks)
Question two
a. Give two reasons why different polymers have different properties. (2mks)
b. What do you understand by the following terms as used in material science (4mks)
i. Condensation polymerization
ii. Degree of polymerization
iii. Amorphous ceramic
iv. Particle composites
c. Wood being fibrous in nature is highly anisotropic. Explain (2mks)
d. Explain clearly how a pre-stressed concrete works. (6mks)
Question three
a. How in reference to engineering materials do the terms stress and strain differ? (2mks)
b. A mild steel bar of 25mm diameter, 20 cm gauge length has an extension of 0.15mm under the load of 7.5 tonnes. Load at elastic limit is 16 tonnes and maximum load is 25 tonnes. Total extension is 5.5 cm. Diameter of the rod at fracture is 1.85 cm. Find:
i. The elastic limit stress. (2mks)
ii. Young’s modulus (2mks)
iii. Percentage elongation (1mk)
iv. Percentage reduction in area. (1mk)
c. A round bar of a metal which is 9mm in diameter and 250mm in length extends by an amount of 0.225 mm under a load of 11.8kN. At the same time, its diameter contracts by 0.00227. determine;
i. Young’s modulus (3mks)
ii. Shear modulus (3mks)
Question four
a. A 20,000N load is applied to a steel bar of cross-sectional area of 6 square cm. when the same load is applied to an aluminum bar it is found to give the same elastic strain as the steel. Calculate the cross-sectional area of the aluminium bar. Young’s modulus of steel is 2.1x10^5 MN/square meter and for aluminium is 0.703x10^5 MN/square meter. (3mks)
b. A 6m long hollow bar of circular cross section area has 140 mm diameter for a length of 4m, while it has 120 mm diameter for a length of 2m. The bore diameter is 80mm throughout the length. Find the elongation of the bar, when it is subjected to an axial tensile force of 300kN. Take modulus of elasticity for the bar material as 200GPa. (4mks)
c. A hollow steel tube 3.5 m long has an external diameter of 120mm. in order to determine the internal diameter, the tube was subjected to a tensile load of 400kN and extension was measured to be 2mm. if the modulus of elasticity for tube material is 200,000 N/square mm, determine the internal diameter of the tube (in mm) (4mks)
d. A reinforced concrete circular section of 50,000 square mm cross-section area carries 6 reinforcing bars whose total area is 500 square mm. find the safe load the column can carry if the concrete is not to stress more than 3.5MPa. Take modular ratio for steel and concrete as 18.
Question five
a. In a tension test on a mild steel rod of 16 mm diameter using 80mm gauge
Length, the following observations were made:
i. Extension under load of 150kN – 0.28mm
ii. Load at yield point – 311kN
iii. Ultimate load – 300kN
iv. Breaking load – 290kN
v. Length between the gauge marks after fracture – 7.40mm
The diameter at fracture was 12.4 mm.
From the above data compute the following engineering material properties:
i. Young’s modulus (1mk)
ii. Yield stress (1mk)
iii. Ultimate stress (1mk)
iv. Engineering stress (1mk)
v. True stress (1mk)
vi. Percentage elongation (2mks)
vii. Percentage reduction in area (2mks)
b. A steel wire ABC 16 m long having cross-sectional area of 4 square mm weighs 20 N. the distance between A and B is same as distance between Band C and is 8m. if the modulus of elasticity of the wire material is 200GPa, find the deformations (in mm) at C and B. (5mks)
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