ST. MOTHER THERESA ENGINEERING COLLEGE, VAGAIKULAM.
B.E.,/B.Tech.,DEGREE EXAMINATION
DEPARTMENT OF MECHANICAL ENGINEERING
MODEL EXAMINATION
Third year/Fifth Semester
ME 6503 – DESIGN OF MACHINE ELEMENTS
1. List the important factors that influence the magnitude of factor of safety. (Nov 2011)
i) Material properties
ii) Nature of load
iii) Presence of localized stresses
iv) Presence of initial stress
v) Mode of failure.
2. State the various methods of finding stresses concentration factors?
a. Photo elasticity method
b. Grid method
c. Brittle coating method
d. Strain gauge method
e. Finite element techniques
3. Definethe term criticalspeed of a shaft.
The speed at which the shaft runs so that the additional deflection ofthe shaft from the axis of
rotation becomes infinite, is known as critical speed.
4. What is shock factor and what does it indicate?
During operation, the shaft is subjected to shock due to bending and twisting conditions. The
shock factor should be multiplied with twisting and bending moments in order to find the equivalent
twisting and bending moments.
5. Give some examples for temporary joints and permanent joints?
Some examples for temporary joints and permanent joints are,
Permanent joints – Riveted joints, Welded joints, bonded joints
Temporary joints – Threaded joints, cotter joints, knuckle joints.
6. Determine the safe tensile load for a bolt of M20, Assume a safe tensile stress of 40 Mpa?
From PSGDB 5.42, for M20,
Stress area Ac = 245 mm2,
= P / Ac => P = Ac = 40 x 245 = 9800 N.
7. Whatarethe endconditionsofthe spring?
(i) plain end
(ii) plain and ground end
(iii) squared end
(iv) Squaredandgroundend.
8. Howdoes the function of flywheel differfrom that ofgovernor?
A governor regulates the mean speed of an engine when there are variations in the mean loads.It
automatically controls the supply of working fluid to engine iththe varying load condition and keeps the
mean speed with in the limits.It does not control the speed variation caused by the varying load.A
flywheel does not maintain constant speed.
9. Listanyfour advantages to rollingcontact bearings over slidingcontact bearings?
Startingfriction is low
Lubrication is simple
It requires lessaxial space and morediametric space
Heavierloads and higherspeeds arepermissible
10. Define static capacity of bearing.
It is defined as load acting on a non-rotating bearing under which permanent deformation is
0.0001 times the ball or roller diameter.
Part-B (5X13=65 Marks)
11)A) A hollow circular column of external diameter 250mm and internal diameter
200mm carries a projecting bracket on which a load of 20kN rests, as shown.
The centre of the load from the centre of the column is 500mm. Find the stresses at the
sides of the column All dimensions are in mm. (Nov/Dec2016)
Ans:
11) B) A C- Clamp is subjected to maximum load of W, as shown in fig. If the maximum tensile
stress in the clamp is limited to 140MPa. Find the value of load W.
12) A) The shaft of length 1 m carrying two pulleys 1 and 2 at its left and right ends respectively and it is supported on
two bearings A and B which are located 0.25 m from the left end and the same 0.25 m from the righ end respectively. The
shaft transmits 7.5 kW power at 360 rpm from pulley 1 to pulley 2. The diameters of pulley 1 and 2 are 10 kg and 30 kg
respectively. The belt tension act vertically downward and ratio of belt tensions on tight side to slack side for each pulley
is 2.5:1. The yield strength of the shaft material σ y = 380 MPa and factor of safety is 3. Estimate the suitable diameter of
the shaft.
12) B) Design a bushed pin type of flexible coupling for connecting a motor and a pump shaft. The following data are
provided: Power transmitted = 20 kW; speed = 1000 rpm; Diameter of the motor and pump shafts = 50 mm.
Allowable bearing pressure in the rubber bush = 0.3 MPa.
13)A) A rectangular cross-section bar is welded to a support by means of fillet welds as shown in Fig. Determine the size
of the welds, if the permissible shear stress in the weld is limited to 75 MPa.
13) B) Design and draw a cotter joint to support a load varying from 30 kN in compression to 30 kN in tension. The
material used is carbon steel for which the following allowable stresses may be used. The load is applied statically.
Tensile stress = compressive stress = 50 MPa; shear stress = 35 MPa and crushing stress = 90 MPa.
14)A) Design and draw a cast iron flywheel used for a four stroke I.C engine developing 180 kW at 240 rpm. The hoop or
centrifugal stress developed in the flywheel is 5.2 MPa, the total fluctuation of speed is to be limited to 3% of the mean
speed. The work done during the power stroke is 1/3 more than the average work done during the hole cycle. The
maximum torque on the shaft is twice the mean torque. The density of cast iron is 7220 kg/m 3.
14)B) A helical compression spring made of oil tempered carbon steel, is subjected to a load which varies from 400 N to
1000 N. The spring index is 6 and the design factor of safety is 1.25. If the yield stress in shear is 770 MPa and
endurance stess in shear is 350 MPa, find: 1. Size of the spring wire, 2. Diameter of the spring, 3. Number of turns of the
spring, and 4. Free length of the spring. The compression of the spring at the maximum load is 30 mm. The modulus of
rigidity for the spring material may be taken as 80 kN/mm 2.
15. (a) Design a journal bearing for a centrifugal pump with the following data:
Diameter of the journal = 150 mm
Load on bearing = 40 kN
Speed of journal = 900 rpm
15) B)Following data is given for a 360o hydro dynamic bearing:
Journal diameter = 100 mm, Radial clearance = 0.12 mm, Radial load =50 kN,
Bearing length = 100 mm, Journal speed = 1440 rpm, Viscosity of lubricant = 16 centipoise.
Calculate: 1. Minimum film thickness 2. Co-efficient of friction 3. Power cost in friction.
PART-C (1X15=15)
16)A) A single row deep groove ball bearing no: 6002 is subjected to an axial thrust load of 1000N and
a radial load of 2200N. find the expected life that 50% of the bearing will complete under this
condition.
16)B) Design a close coiled helical compression spring for a service load ranging from 2250 N to 2750 N. The axial
deflection of the spring for the load range is 6 mm. Assume a spring index of 5. The permissible shear stress intensity is
420 MPa and modulus of rigidity, G = 84 kN/mm 2. Neglect the effect of stress concentration. Draw a fully dimensioned
sketch of the spring, showing details of the finish of the end coils.
