### DESIGN OF MACHINE ELEMENTS Questions Bank 2014

Anna University, Chennai 16 MARKS

DESIGN OF MACHINE ELEMENTS

UNIT- I (STEADY STRESSES AND VARIABLE STRESSES IN MACHINE MEMBERS)

1. (a) A piston of a reciprocating compressor has a diameter of 60mm. The

maximum pressure on the piston fall is 1.25MN/m2.Assuming the gudgeon

pin passing through the small end of the connecting rod can be safely loaded

in shear up to 10MN/m2, Calculate the minimum diameter of the gudgeon

pin. (8)

(b) Explain with mathematical expressions. Maximum principal stress theory

and Von-Mises-Henky theory (8)

2. (a) Determine the diameter of the steel bar, which is a ductile in a nature

subjected to an axial load of 60KN and torsional moment of 1600N-m.Use

the factor of safety 2.5.E=200GPa. (8)

(b) Explain with mathematical expressions. Maximum shear theory and

Venant's theory (8)

ME2303– DESIGN OF MACHINE ELEMENTS

3. A steel member is subjected to a 3-D stress system and resulting principal

stress are 120N/mm2 tension, 80N/mm2and 40N/mm2 compression. If the

proportional limit of the material in simple tension is 280N/mm2 and its

poison's ratio is O.3.Determine the factor of safety according to (a)

Maximum principal stress theory (b) Maximum principal strain theory (c)

Maximum shear stress theory. (16)

4. A bolt is subjected to a tensile load of 25KN and a shear load of 10KN.

Determine the diameter of the bolt according to (a) Maximum principal

stress theory (b) Maximum principal strain theory (c) Maximum shear stress

theory. Assume factor of safety 2.5, Yield point stress in simple tension

300N/mm2, Poisson's ratio is 0.25. (16)

5. Taking stress concentration in to account find the maximum stress

induced when a tensile load of 20KN is applied to (i) A rectangular plate

80mm wide and 12mm thick with a transverse hole of 16mm diameter.(ii)A

stepped shaft of diameters 60mm and 30mm width a fillet radius of

6mm.(16)

6. A circular bar is simply supported with a span of 0.5mand is subjected to

a concentrated cyclic load at its midspan. The load varies from a minimum

value of20KN to maximum value of 45 KN. The load 3 direction is transverse

to the shaft axis. Decide upon the diameter of the bar taking a factor of

safety of 1.5 and factor of 0.85 and 0.89 respectively for size effect and

surface finish. Take often following values for material properties. Ultimate

strength = 650N/mm2, Yield strength = 450N/mm2

Endurance strength =350N/mm2 (16)

7. The bending stress in a machine part fluctuates between a tensile stress

of 280N/mm2 and a compressive stress of 140N/mm2. What should be the

minimum ultimate tensile strength of this part to carry this fluctuation

indefinitely according to (i) Goodman's formula (ii) Soderberg formula Factor

of safety is 1. 75. Assume that the yield point is never likely to be less than

55% of the Ultimate tensile strength or greater than 93 % of it. (16)

8. Determine the thickness of a 120mm wide uniform plate for safe

continuous operation if the plate is to be subjected to a tensile load that has

a maximum value of 1000N.The properties of the plate materials are as

follows. Endurance limit stress is 225MPa and yield point stress is

300MPa.The factor of safety based on yield point may be taken as 1.5. (16)

9. A hot rolled bar of steel is subjected to a torsional load varying from-

150N-m to 450N-m. Determine the required diameter of the bar using a

factor of safety of 1.7. Properties of the material may be assumed as follow.

Ultimate tensile stress = 450MPa Yield stress = 300MPa (16)

10.A transmission of shaft made C45 steel subjected to a fluctuating torque

varying from -100N-m to +500N-m.Also a fluctuating bending moment acts

on the shaft which varies from +500N-m to -500Nm. Let the stress

concentration factor be 2. The shaft is machined for a factor of safety

1.5.Determine the required diameter of the shaft. (16)

UNIT -II (DESIGN OF SHAFTS, KEYS AND COUPLINGS)

1. A line shaft rotating at 200rpm is to transmit 20KW power. the allowable

shear stress for the shaft material is 42N/mm2.If the shaft carries a central

load of 900N and is simply supported between bearing 3meters apart

determine the diameter of the shaft. The maximum tensile or compressive

stress is not to exceed 56N/mm2 (16)

2. An electric generator rotates at 200rpm and receives 300KW from the

driving engine. The armature of the generator is 60cm long and located

between bearing 120cm center to center. Owing to the combined weight of

armature and magnetic pull, the shaft is subjected to 9000kg acting at right

angles to the shaft. The ultimate stress for the shaft is 4480kg/cm2 and

shear stress is 3920kg/cm2.Find the diameter of the shaft for a factor of

safety of 6. (16)

3. A mild steel shaft transmit 23KW to 200rpm.It carries a central load of

900N and is simply supported between the bearing 2.5meters apart.

Determine the size of the shaft, if the allowable shear stress is 42MPa and

the maximum tensile or compressive stress is not exceed 56MPa. What size

of the shaft will be required, if it is subjected to gradually applied load? (16)

4. A shaft to transmit 50KW at 1200rpm.It is also subjected to a bending

moment of 275NNm.Allowable shear stress is 60N/mm2.The shaft is not to

twist more than 20 in a length of 2m.G=80XI03N/mm2.Design a shaft. (16)

. A factory line shaft is 4.5m long and is to transmit 75KW at

200rpm.The allowable stress in shear is 45MPa and maximum

allowable twist is 10 in a length of 20mm diameter. Determine the

required shaft diameter. (16)

8. Design and draw a cast iron flange coupling for a mild steel shaft

transmitting 90KW at 250rpm. The allowable shear stress in the shaft

is 40MPa and the angle of twist is not to exceed 10mm in a length of

20mm diameters. The allowable shear stress in the coupling bolt is

30MPa. (16)

9. Design a cast iron protective type flange coupling to transmit 15KW at

900rpm from an electric motor to a compressor. The service factor may

be assumed as 1.35. The following permissible stress may be used: Shear

stress for the shaft, bolt and key material=40MPa Crushing stress for bolt

and key=80Mpa Shear stress for cast iron=8Mpa (16)

10. A rigid type coupling is used to connect two shaft transmit 15KW at

200rpm.The shaft, key and bolts are made ofC45 steel and the coupling is

of C.I. Design the coupling. (16)

11. Design and sketch protective type C.I flange coupling to transmit

10KW at 250rpm. The permissible shear stress for key, shaft, and bolt as

50N/mm2.Take crushing stress of key as 90N/mm2 and shear stress for

C.I as 14N/mm2.Assume maximum torque is 30% higher than mean

torque.

(16)

12. A knuckle joint is to transmit a force of 140KN.Allowable stresses in

tension, shear and compression are 75N/mm2, 65N/mm2 and 140N/mm2

repectively.Design the joint. (16)

UNIT-III (DESIGN OF FASTNERS AND WELDED JOINTS)

I. The cylinder head of a steam engine with 250mm bore is fastened by

eight stud bolts made of 30C8 steel. Maximum pressure inside the cylinder is

1MPa.Determine the bolt size and approximate tightening torque. Take 20%

over load. Assume _y=300MPa. (16)

2. A steam of effective diameter 300mm is subjected to a steam pressure of

1.5N/mm2.The cylinder head is connected by 8 bolts having yield point

330MPa and endurance limit at 240MPa.The bolts are tightened with an

initial per load 1.5 times the steam load. A soft copper gasket is used to

make the joint leak proof. Assuming a factor of safety 2, find engine size of

bolt required. The stiffness factor for copper gasket may be taken as 0.5.

(16)

3. A steam engine cylinder has an effective diameter of350mm and the

maximum steam pressure acting on the cylinder cover is 5N/mm2.calculate

the number and the size of studs are required to fix the cylinder cover.

Assume the permissible stress in the stud 70N/mm2 (16)

4. A plate 100m wide and 12.5mm thick is to be welded to another plate by

means of two parallel fillet welds. The plates are subjected to a load of

50KN.Find the length of the weld so that the maximum stress does not

exceed 56N/mm2. (Do the calculations under static loading). (16)

5. A plate 75mm wide and 10mm thick is jointed with another plate by a

single transverse weld and double parallel fillet as shown in fig. The joint is

subjected to a maximum tensile force of 55KN. The permissible tensile and

shear stress are 70MPa and 50MPa respectively. Find the length of each

parallel fillet weld. (16)

6. Determine the length of the weld run for a plate of size 120mm wide and

15mm thick to be welded to another plate by means of (1) A single

transverse weld (2) Double parallel fillet welds when the joint is subjected to

variable loads. Assume (Tensile stress =70MPa, shear stress =56MPa.) (16)

UNIT -IV (DESIGN OF SPRINGS AND LEVERS)

1. A helical valve spring is to be designed for an operating load range of 90N

to 135N.The deflection of the spring for this load range is 7.5mm.Assuming

a spring index of 10, a permissible shear stress of 480N/mm2 and a

modulus of rigidity of 0.8Xl 05 N/mm2for the material, determine the

dimensions of the spring. (16)

2. A gas engine valve spring is to have a mean diameter 37.5mm.The

maximum load will have to sustain is 450N with a corresponding deflection

of 12.5mm.The spring is to be subjected to repeated loading and fatigue

must be considered a low working stress of 300N/mm2 will be used. Find the

sizefor the wire and number of coil used. Take rigidity of modulus as 0.8XI05

N/mm2 (16)

3. A compressive helical spring is required to exert a minimum force 250N

and maximum force of 600N and the deflection for this change in load to be

15mm. The spring must fit in a hole of 30mm diameter. The load is static.

Ultimate tensile stress is 1393N/mm2 and shear stress is 606Mpa. (16)

4. A closely coil helical spring is made of 10mm diameter steel wire, the coil

consisting of 10 complete turns with a mean diameter of 120mm.The springs

carries an axial pull of 200N.Determine also deflection in the spring, its

stiffness and strain energy stored by it if the modulus of rigidity of the

material is 80KN/mm2 (16)

5. A helical compression of spring made of oil tempered carbon steel is

subjected to a load which varies from 400N to 1000N. The spring index is 6

and the design factor of safety is 1.25.If the yield stress in shear is 770Mpa

,and endurance stress in shear is 350Mpa,find,(1) Size of the spring wire (2)

Diameter of the spring wire (3) Number of turns of the spring (4) Free

length of the spring. The compression of the spring at the maximum load is

30mm.The modulus of rigidity for the spring material may be taken as

80KN/mm2. (16)

6. A semi-elliptical leaf spring of 1m long and is required to resist a load of

50KN.The spring has 15 leaves of which three are full length leaves. The

width of central band is 100mm. All the leaves are to be stressed to

420MPa.The ratio of total depth to width is 3.Take, =2.1Xl05MPa.Determine,

(i) The thickness and width of the leaves. (ii)The initial gap that should be

provided between the full lengths and graduated leaves before assembly.

(iii)The load exerted on the band for the assembly. (16)

7. A leaf spring for a small trailer is to support a load of 8KN. The spring has

8 graduated leaves and 2 free full length leaves of spring steel of safe stress

380MPa.The over all length 1m and the central band is 80mm wide. Taking

ratio of total depth of leaves as 3.Design the spring and also determine the

deflection of the spring. Take, E=2.1XI05MPa. (16)

8. Design of leaf spring for a truck to the following specifications:

Maximum load on the spring = 140KN No of spring = 4 Material for spring

chromium vanadium steel Permissible tensile stress = 600N/mm2 Maximum

number of leaves =10 Span of spring = 1000mm Permissible deflection =

80mm Young's modulus of the spring = 200N/mm2 (16)

9. Design a cantilever leaf spring to absorb 600N-m energy without

exceeding a deflection of 150mm and a stress of 800N/mm2• The length of

the spring is 600mm. The material of the spring is

steel.Take,E=200KN/mm2 (16)

UNIT-V (DESIGN OF BEARING AND FLYWHEELS)

1. Design a journal bearing for a centrifugal pump with the following data:

Diameter of the journal = 150mm Load on bearing = 40KN Speed of journal

= 900rpm (16)

2. Design a journal bearing for a centrifugal pump from the following data:

Load on the journal=20000N, Speed of the journal=900rpm, Type of oil is

SAElO, for which the absolute viscosity at 55°C=0.017kg/m-s, Ambient

temperature of oil = 15.50C, Maximum bearing pressure for the

pump=1.5N/mm2.Calculate also mass of the lubricating oil required for

artificial cooling, If the rise of temperature, if the rise of temperature of oil

be limited to lOoC heat dissipation coefficient=1232W/m2/oC (16)

3. A full journal bearing of 50mm diameter and 100mm long has a bearing

pressure of l.4N/mm2• The speed of the journal is 900rpm and the ratio of

journal diameter to the diametric clearance is 1000. The bearing is

lubricated with oil, whose absolute viscosity at the operating temperature of

75°C may be taken as 0.011 kg/m-s. The room temperature is 350C.Find,

(1) The amount of artificial cooling required. (2)The mass of lubricating oil

required, if the difference between the outlet and inlet temperature of the oil

is 10°C. Take specific heat of oil as 1850J/Kg/0C. (16)

4. A 150mm diameter shaft supporting a load of 10KN has a speed of

1500rpm.The shaft run in whose bearing length is 1.5 times the shaft

diameter. If the diametric clearance of bearing is 0.15mm and the absolute

viscosity of the oil at the operating temperature is 0.011 Kg/m-s. Find the

power wasted in friction. (16)

5. The turning moment diagram of a multi-cylinder engine is drawn with a

scale of (1 mm = 1°) on the abscissa and (1 mm = 250 Nm)on the ordinate.

The intercepted between the torque developed by the engine and the mean

resisting torque of the machine, taken in order from one are -350,+800,-

600,+900, 11-550,+450,-650 mm2.The engine is running at a mean speed

fluctuations is limited to 0.02.A rimmed flywheel made of grey cast iron FG

200 (Density=7100Kg/m3) is provided. The spokes, shaft and hub are

assumed to contribute 10% of the required moment of inertia. The rim has

rectangular cross section and the ratio of width to thickness is 1.5.Determine

the dimensions of the rim. (16)