JNTU B.Tech III Year PRINCIPLES OF MACHINE DESIGN Previous Question Paper (May - 2018 - R15)

What do you mean by notch sensitivity?

What is meant by stress concentration? How do you take it into consideration in case of a component subjected to dynamic loading?

What is an economical joint and where does it find applications?

What are flexible couplings and what are their applications?

Discuss the different types of pulleys used in belt drives.

What are the advantages and disadvantages of V-belt drive over flat belt drive?

State the two most important reasons for adopting involute curves for a gear tooth profile.

Explain the different causes of gear tooth failures and suggest possible remedies to avoid such failures.

Explain with reference to a neat plot the importance of the bearing characteristic curve.

How do you express the life of a bearing? What is an average or median life?

What is meant by ‘hole basis system’ and ‘shaft basis system’? Which one is preferred and why?

A machine component is subjected to a flexural stress which fluctuates between +300 MN/m² and -150 MN/m². Determine the value of minimum ultimate strength according to:

i) Gerber relation

ii) Modified Goodman relation

iii) Soderberg relation.

A cantilever beam made of cold drawn carbon steel of circular cross-section is subjected to a load which varies from -F to 3F. Determine the maximum load that this member can withstand for an indefinite life using a factor of safety as 2. The theoretical stress concentration factor is 1.42 and the notch sensitivity is 0.9. Assume: Ultimate stress = 550 MPa, Yield stress = 470 MPa, Endurance limit = 275 MPa, Size factor = 0.85, Surface finish factor = 0.89.

The load on a bolt consists of an axial pull of 10 kN together with a transverse shear force of 5 kN. Find the diameter of bolt required according to:

i) Maximum principal stress theory

ii) Maximum shear stress theory

iii) Maximum principal strain theory

iv) Maximum strain energy theory

v) Maximum distortion energy theory

Take permissible tensile stress at elastic limit = 100 MPa and poisson’s ratio = 0.3.

How are the keys classified? Draw neat sketches of different types of keys and state their applications.

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. The load is applied statically. Tensile stress = compressive stress = 50 MPa; shear stress = 35 MPa and crushing stress = 90 MPa.

Sketch and discuss the various types of welded joints used in pressure vessels. What are the considerations involved?

Two lengths of mild steel tie rod having width 200 mm and thickness 12.5 mm are to be connected by means of a butt joint with double cover plates. Design the joint if the permissible stresses are 80 MPa in tension, 65 MPa in shear and 160 MPa in crushing. Make a sketch of the joint.

Derive the relation for the ratio of driving tensions of a V-belt.

Design a cast iron driven pulley to transmit 20 kW at 300 r.p.m. The diameter of the pulley is 500 mm and the angle of lap is 180^o. The pulley has four arms of elliptical cross-section with major axis twice the minor axis. The coefficient of friction is 0.3. The allowable tension per metre width of the belt is 2.5 N. Shear stress for shaft = 50 MPa, Bending stress for arms = 15 MPa.

An open belt connects two flat pulleys. The pulley diameters are 300 mm and 450 mm. The smaller pulley runs at 200 r.p.m. Coefficient of friction is 0.25. It is found that the belt is on the point of slipping when 3 kW is transmitted. Find the percentage increase in power possible by (i) increasing the initial tension by 10%, and (ii) increasing the coefficient of friction by 10%.

A pulley of 0.9 m diameter revolving at 200 RPM is to transmit 7.5 kW. Find the width of a leather belt if the maximum tension is not to exceed 145 N in 10 mm width. The tension in the tight side is twice that in the slack side. Determine the diameter of the shaft and dimensions of pulley parts, assuming six arms. Maximum shear stress is 63 MPa.

A helical cast steel gear with 30^o helix angle has to transmit 35 kW at 1500 rpm. If the gear has 24 teeth, determine the necessary module, pitch diameter and face width for 20^o full depth teeth. The static stress is 56 MPa. Face width = 3 times normal pitch. What is the end thrust?

Write the expressions for static strength, limiting wear load and dynamic load for helical gears and explain the various terms used.

Explain the phenomenon of interference in involute gears. What are the conditions to be satisfied in order to avoid interference?

A motor shaft rotating at 1500 r.p.m. has to transmit 15 kW to a low speed shaft with a speed reduction of 3:1. The teeth are 14.5^o involute with 25 teeth on the pinion. Steel with 200 MPa safe stress. Shaft safe stress 40 MPa. Design a spur gear drive. Assume starting torque 25% higher than running torque.

A cylindrical roller bearing with bore diameter of 40 mm is subjected to a radial force of 25 kN. The coefficient of friction is 0.0012 and the speed of rotation is 1440 rpm. Calculate the power lost in friction.

What are rolling contact bearings? Discuss their advantages over sliding contact bearings.

A ball bearing is subjected to a radial force of 2500 N and an axial force of 1000 N. The dynamic load carrying capacity of the bearing is 7350 N. The values of X and Y factors are 0.56 and 1.6 respectively. The shaft is rotating at 720 rpm. Calculate the life of the bearing.

Write short note on classifications and different types of antifriction bearings.