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NOVEMBER 2008 SUPPLEMENTARY EXAMINATION

SUBJECT NAME: STRENGTH OF MATERIALS II

CODE: SMT211T/SMT101T

DURATION: 3 HOURS

TOTAL MARKS: 100

FULL MARKS: 100

SPECIAL REQUIREMENTS:NON-PROGRAMMABLE POCKET CALCULATORS

INSTRUCTIONS TO CANDIDATES: ANSWER ALL THE QUESTIONS

NUMBER OF PAGES (COVER PAGE INCLUDED) : 3+ APPENDIX

COURSE:

ND: ENGINEERING : MECHANICAL

FIRST EXAMINER:

DA DESAI

SECOND EXAMINER:

MODERATOR:

FM MASHILE

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QUESTION 1

The results of a tensile test on a mild steel specimen are as follows:

original diameter = 20 mm; original gauge length = 40 mm; proportional limit load = 80 kN;

extension at proportional limit = 0.048 mm; yield point load = 85 kN; maximum recordedload = 150 kN; final length between gauge points = 55.6 mm and final minimum diameter

(neck) = 15.8 mm. Calculate:

a) the modulus of elasticity for mild steel;

b) the proportional limit stress;

c) the ultimate tensile stress;

d) the percentage elongation; ande) the percentage reduction in area.

/15/QUESTION 2

Two vertical wires are suspended a distance of 450 mm apart. Their lower ends support a

rigid horizontal bar, which carries a load W. The left-hand wire is made of copper and has a

diameter of 3 mm. The right-hand wire is made of steel and has a diameter of 2 mm.

a) Determine the position ofWfrom the copper wire if the elongation in both wires is the

same.

b) If both wires are initially 3.5 m long, determine the load carried by each wire and the totalelongation ifW= 350 N

Esteel = 200 GPa and Ecopper = 100 GPa.

/15/QUESTION 3

A hollow box beam ABCof length L is supported at end A by a 20 mm diameter pin that

passes through the beam and its supporting pedestals (see figure). The roller support a B islocated at distanceL/3 from endA.

a) Determine the average shear stress in the pin due to a load P= 10 kN.

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b) Determine the average bearing stress between the pin and the box beam if the wall

thickness of the beam = 12 mm.

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QUESTION 4

A solid steel shaft, 100 mm in diameter and 1 m long, is to be coupled in series to a hollow

shaft with an external diameter of 125 mm and an internal diameter of 100 mm. The length

lof the hollow shaft is to be such that when a torque of 15 kN.m is transmitted, the totalangle of twist shall not exceed 2.5o. Determine the maximum permissible value ofland the

torsional stiffness of the compound shaft. G = 80 GPa.

/10/QUESTION 5

A thin rim with a mean diameter of 1.2 m and a cross-section of 15 mm x 200 mm rotates at

800 r/min. Calculate the

a) magnitude of the force and the stress in the rim if the density of the material is 7.8 Mg/m3,and

b) change in diameter due to rotation. E = 200 GPa.

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QUESTION 6

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For the beam ABCDEF shown below:

a) Determine the reactions at the supports; 6b) Draw the Shear Force diagram; 5

c) Draw the Bending Moment diagram; 4

d) Find the maximum Shear Force and maximum Bending Moment; 2e) Determine the point(s) of contraflexure. 8

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