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DEPARTMENT OF MECHANICAL ENGINEERING

MARCH 2010 SEMESTER TEST 1

SUBJECT : SMT 101T/211T/SMM201T

DURATION : 90 MINS

TOTAL MARKS : 50

FULL MARKS : 50 2 = 100

REQUISITES : Non-programmable pocket calculators and drawing instruments may be

used.

NUMBER OF PAGES (INCLUDING THIS PAGE) : 2ANNEXURES ATTACHED : 0

EXAMINERS: D DESAI, L BENEKE

INSTRUCTIONS:

ANSWER ALL QUESTIONS.

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QUESTION 1

a) Explain briefly what you understand by the term creep. (3)

b) Define the termPoissons ratio. (2)

c) Explain the difference between true stress and engineering stress. (3)

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QUESTION 2

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 recorded

load = 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; (6)

b) the proportional limit stress; (3)

c) the ultimate tensile stress; (4)

d) the percentage elongation. (2)

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QUESTION 3

The inclined ladderAB supports a house painter (82 kg) at Cand the self weight (q = 36 N/m)

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of the ladder itself. Each ladder rail (tr= 4 mm) is supported by a shoe (ts = 5 mm) which is

attached to the ladder rail by a 8 mm diameter bolt (dp = 8 mm).

a) Find the support reactions atA andB (note: directions of reactions are assumed in the figure). (6)

b) Find the resultant force in the shoe bolt atA. (3)

c) Find the maximum average shear and bearing stresses in the shoe bolt at A. (6)

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QUESTION 4

A rigid bar of weight W= 800 N hangs from three equally spaced vertical wires (lengthL = 150 mm, spacing a = 50 mm): two of steel and one of aluminum. The wires also support

a loadPacting on the bar. The diameter of the steel wires is ds= 2 mm, and the diameter

of the aluminum wire is da= 4 mm. AssumeEs= 210 GPa andEa= 70 GPa.

(a) What loadPallow can be supported at the midpoint of the bar(x = a) if the allowable stress in

the steel wires is 220 MPa and in the aluminum wire is 80 MPa? (See figure below).

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TOTAL MARKS = (50)

FULL MARKS = 50 2 = [100]

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MEMORANDUM

MARCH 2010 SEMESTER TEST 1

QUESTION 1

a) When some materials are loaded for long periods of time, they develop additional strains.

This phenomenon is known as creep. (3)

b) The ratio of lateral strain to axial (longitudinal) strain. (2)

c) True stress : The actual cross-sectional area at the narrow part of the neck is

used to calculate the stress. Engineering stress :The initial (original) cross-sectional area

at the narrow part of the neck is used to calculate the stress (3)

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