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Posted Date: 30 Sep 2009 Posted By: Sree.... Member Level: Platinum
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2007 Andhra Pradesh State Jawaharlal Nehru Technological University Code No: R05312401 III B.Tech I Semester Regular Examinations, November 2007 DESIGN OF MACHINE ELEMENTS [Set No. 2] Question paper
Code No: R05312401 Set No. 2
III B.Tech I Semester Regular Examinations, November 2007
DESIGN OF MACHINE ELEMENTS
(Automobile Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
1. Enumerate the factors to be considered while selecting the materials for machine
parts. Recommend suitable materials for each of the following components :
(a) Crankshaft
(b) Body of electric motor
(c) Worm gear
(d) Piston for motor car engine
(e) Lathe bed
(f) Bearing bush [16]
2. (a) Explain the Modified Goodman’s line theory for designing the components
subjected to fatigue loads
(b) A thin wall cylindrical pressure vessel of mean diameter of 60 cm is subjected
to internal pressure varying from 0 to 40 MPa. Find the required thickness
of the pressure vessel based on yield point of 400 MPa, endurance limit of 22
Mpa, and a factor of safety of 3. Use Soderberg criterion of failure. [6+10]
3. (a) What do you mean by efficiency of riveted joint?
(b) A locomotive boiler of 1.8 m internal diameter is required to generate steam
at 1.4 MPa gauge. Calculate the thickness of the shell plate and design the
triple riveted longitudinal double butt strap joint with unequal straps. Use
the following data:
st= 77 MPa, t= 60 MPa and sc= 135 MPa. Efficiency of triple-riveted lon-
gitudinal butt joint is 84%. [4+12]
4. (a) What is the function of transmission shaft?
(b) A machinery shaft is subjected to torsion only. The bearings are 2.40 metre
apart. The shaft transmits 187.5 kW at 200 rev/min. Allow a shear stress of
42 MPa after an allowance for keyways.
i. Determine the shaft diameter for steady loading
ii. Determine the shaft diameter if the load is suddenly applied with minor
shocks. [2+14]
5. (a) Under What circumstances, concentric springs are preferred?
1 of 2
Code No: R05312401 Set No. 2
(b) A rail carriage weighing 200kN and running at 5 km/hour is brought to rest by
four buffer springs of close coiled helical type during connection with another
carriage which is already at rest. The mean coil diameter is 5 times the wire
diameter. The deflection of each spring is 220 mm, to bring the carriage to
rest. Safe shear stress for the spring material is 400 N/mm2. Calculate the
maximum load on the spring, diameter of wire and coil, number of turns and
free length of spring. Assume the ends of spring are squared and ground. Take
G= 0.8×104N/mm2. [2+14]
6. (a) What are the commonly used materials for sliding contact bearings?
(b) A ball bearing subjected to a radial load of 5kN is expected to have a life
of 8000 hours at 1450 r.p.m with a reliability of 99%. Calculate the dynamic
load capacity of the bearing so that it can be selected from the manufacturer?s
catalogue based on a reliability of 90%. [2+14]
7. Design a connecting rod of I cross section for an automobile diesel engine of the
following specifications.
Diameter of cylinder=100mm
Stroke length =125mm
Maximum combustion pressure =2.8MPa
Maximum engine speed=2000rpm
Weight of the reciprocating parts =1.1kg
Length of connecting rod between centers=31.5cm
Assume an allowable crushing stress =3000kg/cm2. [16]
8. Design a Cast iron piston for a single acting four stroke engine for the following
specifications.
Cylinder bore = 100mm, Stroke = 120mm, Maximum gas pressure = 5N/mm2,
Break mean effective pressure = 0.65N/mm2, Fuel consumption = 0.227kg/kW/hr,
Speed =2200 rev/min, Assume suitable data. [16]
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