DEPARTMENT OF MECHANICAL ENGINEERING, BIT, DURG

Semester: 6th Section: A & B Subject: Design of Machine Elements

Unit: 1

(a) Short Questions:

1) What is factor of safety?

2) State the factors influencing factor of safety.
3) What is meant by design stress or working stress?
4) Briefly discuss about theoretical stress concentration.
5) State the cause of stress concentration.
6) What are the methods for reducing stress concentration?
7) What are the various theories of failures?
8) State maximum principal stress theory.
9) State maximum shear stress theory.
10) State distortion energy theory.
11) What is fluctuating stress and its type?
12) What is reversed and repeated stress?
13) What is mean and variable stress?
14) Briefly discuss about fatigue stress concentration.
15) What are the different failure modes of machine component?
16) What is notch sensitivity factor?
17) Define endurance limit and fatigue life.

(b) Descriptive Questions:

1. A flat plate subjected to a tensile force of 5 kN as shown in fig. The plate material is grey
cast iron FG 200 and the factor of safety is 2.5. Determine the thickness of the plate.

2. A Non-rotating shaft supporting a load of 2.5 kN is shown in fig. The shaft is made of
brittle material with an ultimate tensile strength of 300 N/mm2. The factor of safety is 3.
Determine the dimensions of the shaft.
3. A cantilever beam made of cold drawn steel 20C8 (Sut = 540N/mm2) is subjected to a
completely reversed load of 1000 N as shown in fig. The notch sensitivity factor q at the
fillet can be taken as 0.85 and the expected reliability is 90%. Determine the diameter d
of the beam for a life of 10000 cycles.

4. A cantilever beam made of cold drawn steel 40C8 (Sut = 600N/mm2 and Syt = 380
N/mm2) is shown in fig below. The force P acting at the free end varies from -50 N to
+150 N. The expected reliability is 90% and the factor of safety is 2. The notch
sensitivity factor at the fillet is 0.9. Determine the diameter of the beam at the fillet cross-
section.

5. A transmission shaft of cold drawn steel 27Mn2 (Sut = 500N/mm2 and Syt = 300 N/mm2)
is subjected to a fluctuating torque which varies from -100 to +400 N-m. The factor of
safety is 2 and expected reliability is 90 %. Neglecting the effect of stress concentration
factor determine the diameter of the shaft. Assume the distortion energy theory of failure.

6. A round shaft made of a brittle material and subjected to a bending moment of 15 N-m as
shown in fig. The stress concentration factor at the fillet is 1.5 and the ultimate tensile
strength of the shaft material is 200 N/mm2.Determine the shaft diameter d, the
magnitude of stress at the fillet and factor of safety.
7. Draw SN curve for steel and explain:- (a) Design for infinite life. (b) Design for finite life

8. Explain maximum principal stress theory.

9. Explain maximum shear stress theory.

10. Explain distortion energy theory.

11. Explain Modified Goodman Diagram for axial and bending fluctuating stress.

12. Explain Modified Goodman Diagram for fluctuating tensional shear stress.

13. A solid circular shaft , 15 mm in diameter, is subjected to torsional shear stress, which
varies from 0 to 35 N/mm2 and at the same time, is subjected to an axial stress that
various from -15 to +30 N/mm2. The shaft is made of steel FeE400 (Sut = 600 N/mm2 and
Syt = 380 N/mm2) and the corrected endurance limit of the shaft is 200 N/mm2.
Determine the factor of safety.

14. A rotating shaft subjected to a non-rotating force of 5 kN and simply supported between
two bearings A and E as shown in figure. The shaft is machined from plain carbon steel
30C8 (Sut = 500 N/mm2) and the expected reliability is 90%. The equivalent notch radius
at the fillet section can be taken as 3 mm. what is the life of the shaft?

15. A forged steel bar 50 mm in diameter is subjected to a reversed bending stress of 250
N/mm2. The bar is made of steel 40C8 (Sut = 600 N/mm2). Calculate the life of the bar for
a reliability of 90%.
16. A machine component is subjected to two-directional stress. The tensile stress in the X
direction various from 40 to 100 N/mm2 while the tensile stress in Y direction various
from 10 to 80 N/mm2. The frequency of variation of these stresses is equal. The corrected
endurance limit of the component is 270 N/mm2. Take Sut = 660 N/mm2. Find factor of
safety used by the designer.
17. The polished steel bar is subjected to axial tensile force that various from zero to Pmax. it
has a groove 2 mm deep and having a radius of 3 mm. the theoretical stress
concentration factor and notch sensitivity factor at the groove are 1.8 and 0.95
respectively. The outer diameter of the bar is 30 mm. Take Sut = 1250 MPa. The
endurance limit in reversed bending is 600 MPa. Find the maximum force that the bar can
carry for 105 cycle with 90% reliability.
 Unit: II

(a) Short Questions:

1) What is function of key and its types?

2) What is coupling? Describe the types of couplings.
3) What is the effect of keyway cut into the shaft?
4) Differentiate saddle key and sunk key.
5) What are the different failure modes of cotter?
6) Define woodruff key.
7) Define splines.
8) Define kennedy key.
9) Differentiate rigid and flexible coupling.

(b) Descriptive Questions:

1. Design and draw a cotter joint to support a load varying from 30kN in compression to
30kN 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 =
50MPa; shear stress = 35MPa and crushing stress = 90MPa.
2. It is required to design a cotter joint to connect two steel rod of equal diameter. Each rod
is subjected to an axial tensile force of 50 kn. Design the joint and specify its main
dimensions.
3. Design a sleeve and cotter joint to resist a tensile load of 60 kN. All parts of the joint are
made of the same material with the following allowable stresses: σt = 60 MPa; τ = 70
MPa; and σc = 125 MPa.
4. Design a knuckle joint to transmit 150 kN. The design stress may be taken as 75 MPa in
tension, 60 MPa in shear and 150 MPa in crushing.
5. A standard cross section for a flat key which is fitted on a 50mm diameter shaft is 16 x 10
mm. the key is transmitting 475 N-m torque from the shaft to the hub. The key is made of
commercial steel (Syt = Syc= 230 N/mm2). Determine the length of the key if the factor of
safety is 3.
6. A standard splined connection 8 x 52 x 60 mm is used for the gear and the shaft assembly of
a gear box. A 20 kW power at 300 rpm is transmitted by the splines. The dimensions of the
splines are Major diameter = 60 mm Minor diameter = 52 mm No. of splines = 8. The normal
pressure on the splines is limited to 6.5 N/mm2. The coefficient of friction is 0.06. Calculate
(i) length of the hub of the gear & (ii) The force required to shift the gear.
7. Design a muff coupling which is used to connect two steel shafts transmitting 25 kW power
at 360 rpm. The shafts and key are made of plain carbon steel 30C8 (Syt = Syc = 400 N/mm2).
The sleeve is made of grey cast iron FG 200 (Sut= 200 N/mm2). The factor of safety for the
shafts and key is 4. For sleeve the factor of safety is 6 based on ultimate strength.
8. Design a rigid muff coupling. Use CI for the muff. The power transmitted is 25 kW at 300
rpm. Ultimate tensile strength =200 MPa and factor of safety =6. Use 30C8 for the shaft
considered. Yield Point stress = 330 Mpa and factor of safety =4.
9. It is required to design a rigid type of flange coupling to connect two shafts. The input
shaft transmits 37.5 kW power at 180 rpm to the output shaft through the coupling. The
service factor for the application is 1.5 i.e. the design torque is 1.5 times of the rated
 torque. Select material for various parts of the coupling. Design the coupling and specify
the dimensions of its components.
10. Design a cast iron protective type flange coupling to transmit 15 kW at 900 rpm from an
electric motor to a compressor. The service factor may be assumed as 1.35. The following
permissible stresses may be used: Shear stress for shaft, bolt and key material = 40 MPa
Crushing stress for bolt and key = 80 MPa, Shear stress for cast iron = 8 MPa Draw also a
neat sketch of the coupling.
11. It is required to design a bushed-pin type flexible coupling to connect the output shaft of
an electric motor to the shaft of a centrifugal pump. The motor delivers 20kW power at
720 rpm. The starting torque of the motor can be assumed to 150% of the rated torque.
Design the coupling and specify the dimensions of its components.