Machine Design
(Multiple Choice Questions)
1. The ultimate strength of steel in tension in comparison to shear is in the ratio of
(a) 1 : l
(b) 2:1
(c) 3 : 2
(d) 2 : 3
(e) 1 : 2
Ans: c

2. The pci Tnissible stress for carbon steel under static loading is generally taken as
(a) 2000-3000 kg/pm2
(b) 3000-4000 kg/cm2
(c) 4000-J500 kg/cm2
(d) 7500-10,000 kg/cm2
(e) 10,000-15,000 kg/cm2.
Ans: c

3. The property of a material which enables it to resist fracture due to high impact loads is known as
(a) elasticity
(b) endurance
(c) strength
(d) toughness
(e) resilience.
Ans: d

4. A hot short metal is
(a) brittle when cold
(b) brittle when hot
(c) brittle under all conditions
(d) ductile at high temperature
(e) hard when hot.
Ans: b

5. Guest's theory of failure is applicable for following type of materials
(a) brittle
(b) ductile
(c) elastic
(d) plastic
(e) tough.
Ans: b

6. Rankine's theory of failure is applicable for following type of materials
(a) brittle
(b) ductile
(c) elastic
(d) plastic
(e) tough.
Ans: a

7. If an unsupported uniform cross sectional elastic bar is subjected to a longitudinal impact from a rigid bob moving with velocity v, then a compressive wave of intensity sc is propagated through the bar as follows (a) vpE
(b) vVvF
(c) WpE/2
(d) IvHpE
(e) none of the above, where E = modulus of elasticity and p = mass density.

Ans: a

8. Tensile strength of a mild steel specimen can be roughly predicted from following hardness test
(a) Brinell
(b) Rockwell
(c) Vicker
(d) Shore's sceleroscope
(e) none of the above.
Ans: a

9. Resilience of a material is important, when it is subjected to
(a) combined loading
(b) fatigue
(c) thermal stresses
(d) wear and tear
(e) shock loading.
Ans: e

10. In the case of an elastic bar fixed at upper end and loaded by a falling weight at lower end, the shock load produced can be decreased by
(a) decreasing the cross-section area of' bar
(b) increasing the cross-section area of bar
(c) remain unaffected with cross-section area
(d) would depend upon other factors
(e) none of the above.
Ans: a

11. .Other method of reducing shock load in the above case can be
(a) to decrease length
(b) to increase length
(c) unaffected by length
(d) other factors would decide same
(e) none of the above.

Ans: b

12. If a load W is applied instantaneously on a bar; then the stress induced in bar will
(a) be independent of ratio of mass of load W to mass of bar (y)
(b) increase with increase in y
(c) decrease with decrease in y
(d) depend on other considerations
(e) none of the above.
Ans: a

13. Brittle coating technique is used for
(a) determining brittleness
(b) protecting metal against corrosion
(c) protecting metal against wear and tear
(d) experimental stress analysis
(e) non-destructive testing of metals.
Ans: d

14. Stress concentration is caused due to
(a) variation in properties of material from point to point in a member
(b) pitting at points or areas at which loads on a member are applied
(c) abrupt change of section
(d) all of the above
(e) none of the above.
Ans: d

15. The endurance limit of a material with finished surface in comparison to rough surface is
(a) more
(b) less
(c) same
(d) more or less depending on quantum of load
(e) unpredictable.

Ans: a

16. Plastic flow in ductile materials
(a) increases the seriousness of static loading stress concentration
(b) lessens the seriousness of static loading stress concentration
(c) has no effect on it
(d) depends on other considerations
(e) none of the above.
Ans: b

17. The maximum stress due to stress concentration in a bar having circular transverse hole, as compared to its static stress without hole will be
(a) same in both cases
(b) 2 times more
(c) 3 times more
(d) 4 times more
(e) unpredictable.
Ans: c

18. The fatigue life of a part can be improved by
(a) electroplating
(b) polishing
(c) coating
(d) shot peening
(e) heat treating.
Ans: d

19. Stress concentration in static loading is more serious in
(a) ductile materials
(b) brittle materials
(c) equally serious in both cases
(d) depends on other factors
(e) unpredictable.

Ans: b

20. Stress concentration in cyclic loading is more serious in
(a) ductile materials
(b) brittle materials
(c) equally serious in both cases
(d) depends on other factors
(e) unpredictable.
Ans: a

SUBJECTIVE QUESTIONS
UNIT-I
Q.1 What are the different factors should be considered while selecting the materials for the component of machines?
Q.2 What are preferred numbers? Explain their advantages. A manufacturer is interested to start the business with fine different model of machines ranging from 7.5kW to 75kW. Specify the power capacity of models.
Q.3 Discuss BIS system of designation of steels. What do you understand from following designations of materials (1) FG 350 (2) 10C4 (3) 50Cr IV 23?
Q.4 How does the steel designated on the basis of mechanical properties?
Q.5Write a short note on designation of free cutting steels.
Q.6 Give the composition of grey cast iron and discuss the designation of grey cast iron.
Q.7 Write short note on fits.
Q.8 A manufacturer is interested in manufacturing 4 different models of generating sets ranging from 5kW to 50kW capacities. Using R5 series, specify the capacities of the models. If the further wisher wants to expand to 8 models within the same range, what will be the capacities of the additional models?
Q.9 What do you understand by ‘heat resisting steel’?
Q.10 Calculate the tolerances, fundamental deviations and limits of sizes for the shaft designated as
40 H8/f7.
Q.11 The dimensions of the mating parts, according to basic hole system, are given as follows:
Hole:

25.00mm
25.02mm

Shaft:

24.97mm
24.95mm

Find the hole tolerance, shaft tolerance and allowance.
Q.12 Discuss the Indian standard system of limits and fits.
Q.13 Write a short note on bearing materials used in industry.
Q.14 Discuss the designation of stainless steel and heat resisting steel.
Q.15 Write a short note on spheroidal graphite cast iron.
Q.16 Discuss the IS-designation of malleable cast iron.
Q.17 Discuss the compositions and uses of different types of brass.
Q.18 What do you understand by the following designation of materials?
40 C8; 40 Cr1; 35 Ni 1 Cr 60; 50 Cr 1V23; FG 350
Q.19 What are preferred numbers? How will you find the number belonging to R10 series?
Q.20 Designate the steel on the basis of chemical composition as per Indian standard IS : 1570.

UNIT-II
Q.1 Explain Guest’s or Tresca’s theory of failure.
Q.2 Explain the Rankine’s theory of failure.
Q.3 Discuss the maximum distortion energy theory of failure.
Q.4 Discuss the Haigh’s theory of failure.
Q.5 What are the different factors should be considered during selection of factors of safety?
Q.6 What are the necessity of having more than one theories of failure? State maximum shear stress theory and show that it is more suitable for ductile material in comparison to maximum principal stress theory. Q.7 What do you understand by factor of safety?
Q.8 Explain the notch sensitivity in brief.
Q.9 Write short notes on any two of the following:
1. Endurance Limit
2. Stress Concentration
3. Graphical representation of maximum shear stress theory
Q.10 A shaft transmits 5kW at 1000 rpm. Using maximum shear strain energy theory, find the diameter of the shaft. Take yield point stress in tension as 300N/mm2, factor of safety as 2.0 and Poisson’s ratio 0.25.

Q.11 A line shaft rotating at 200rpm, is to transmit 200kW. The allowable shear stress for the material of the shaft is 42Mpa. If the shaft carries a central load of 900N and is simply supported between bearings
3m apart, determine the diameter of the shaft. The maximum tensile or compressive stress is not to exceed 56MPa.

Q.12 A beam of uniform rectangular cross-section is fixed at one end and carries an electric motor weighing 400 N at a distance of 300mm from the fixed end. The maximum bending stress in the beam is
40 MPa. Find the width and depth of the beam, if depth is twice that of the width.
Q.13 A rectangular strut is 150mm wide and 120mm thick. It carries a load of 180kN at an eccentricity of
10mm in a plane bisecting the thickness. Find the maximum and minimum intensities of stress in the section. Q.14 A 50mm diameter shaft is made from carbon steel having ultimate tensile strength of 630MPa. It is subjected to a torque which fluctuates between 2000N-m to 800N-m. Using Soderberg method, calculate the factor of safety. Assume suitable values for any other data needed.
Q.15 A Circular rod made of ductile material has endurance strength of 280N/mm2 and ultimate strength
350N/mm2. The member is subjected to a variable axial load varying from +700kN (tensile) to -300kN
(compressive). Take fatigue stress concentration factor as 1.8 and factor of safety as 2.0. Find the suitable diameter of the Rod.
Q.16 Determine the diameter of a circular rod made of ductile material with fatigue strength (complete stress reversal), σe =265MPa and a tensile yield strength of 350Mpa. The member is subjected to a varying axial load from Wmin= -300 x 103N to Wmax = 700 x x103N and has a stress concentration factor =
1.8.Use factor of safety as 2.0.
Q.17 Determine the size of the piston rod subjected to a total load having cycline fluctuation from 15kN in compression to 25kN in tension. The endurance limit is 360MPa and yield strength is 400Mpa. Take impact factor 1.25, factor of safety = 1.5, surface finish factor = 0.88 and stress concentration factor =
2.25.
Q.18 A machine component is subjected to bending stress which fluctuates between 300N/mm2 tensile and 150N/mm2 compressive in a cycline manner. Using Goodman formula, calculate the minimum required ultimate strength of the material. Take factor of safety as 1.5 and endurance limit in reversed bending as 50% of ultimate strength.
Q.19 A cylindrical shaft made of steel of yield strength 700MPa is subjected to static loads consisting of bending moment 10kN-m and a torsional moment 30kN-m. Determine the diameter of the shaft using two different theories of failure and assuming a factor of safety of 2. Take E = 210GPa and Poisson’s ratio =
0.25.
Q.20 A line shaft rotating at 200rpm, is to transmit 200kW. The allowable shear stress for the material of the shaft is 42MPa. If the shaft carries a central load of 900N and is simply supported between bearings
3m apart, determine the diameter of the shaft. The maximum tensile or compressive stress is not to exceed 56MPa.

UNIT-III
Q.1 What are the different materials used for making rivets?
Q.2 Define the following terms related to rivets:
1. Pitch

2. Back pitch

3. Diagonal pitch

4. Marginal pitch

Q.3 What are the different assumptions made in designing boiler joints?
Q.4 Sketch and discuss various welded joints used in pressure vessels.
Q.5 Explain the strength of a butt joint.
Q.6 What are the requirements of a good shaft coupling?
Q.7 What are the advantages and disadvantages of woodruff key.
Q.8 Design a double riveted butt joint with two cover plates for longitudinal steam boiler shell, 0.75m diameter, to carry a maximum steam pressure of 1.55N/mm2. Assume joint efficiency as 75%, allowable tensile stress in the plate90MPa, compressive stress in plate and rivet 140MPa and shear stress in the plate and rivet 56MPa.
Q.9 A plate 100mm wide and 10mm thick is to be welded to another plate by means of double parallel fillets. The plates are subjected to a static load of 80kN. Find the length of the weld if the permissible shear stress in the weld does not exceed 55MPa.
Q.10 Two lengths of mild steel tie rod having width 200mm and thickness 12.5mm are to be connected by means of a butt joint with double cover plates. Design the joint if the permissible stresses are 80MPa in tension, 65MPa in shear and 160MPa in crushing. Make a sketch of the joint.
Q.11 A double riveted lap joint with chain riveting is to be made for joining two plates of 6mm thickness.
Determine diameter of the rivets, distance between rows of rivets and pitch of rivets. Indicate how the joint will fail? Assume σt = 220MPa,τ = 100MPa ,σc = 150MPa.
Q.12 Design a double riveted butt joint with two cover plates for the longitudinal seam of boiler shell 1.5m in diameter subjected to a steam pressure of 0.95N/mm2. Assume joint efficiency as 75%, allowable tensile stress in the plate 90MPa; compressive stress 140MPa and shear stress in the rivet 56MPa.

Q.13 A double riveted double cover butt joint in plates 20mm thick is made with 25mm diameter rivets at
100mm pitch. The permissible stresses are:
Assume σt = 120MPa,τ = 100MPa ,σc = 150MPa
Find the efficiency of joint, taking the strength of the rivet in double shear as twice than that of single shear. Q.14 Design the rectangular key for a shaft of 75mm diameter. The shearing and crushing stresses for key material are 50MPa and 75MPa respectively.
Q.15 A line shaft rotating at 200rpm is to transmit 20kW. The shaft may be assumed to be made of mild steel with an allowable shear stress of 42MPa. Determine the diameter of the shaft, neglecting the bending moment on the shaft.
Q.16 Find the diameter of a solid steel shaft to transmit 20kW at 200rpm. The ultimate shear stress for the steel may be taken as 360MPa and a factor of safety as 8. If a hollow shaft is to be used in place of the solid shaft then find the inside and outside diameters when the ratio of inside and outside diameters is
0.5.
Q.17 A steel spindle transmits 4kW at 800rpm. The angular deflection should not exceed 0.25 per metre of the spindle. If the modulus of rigidity for the material of the spindle is 84GPa, find the diameter of the spindle and the shear stress induced in the spindle.
Q.18 An universal coupling is used to connect two mild steel shafts transmitting a torque of 5000Nm.
Assuming that the shafts are subjected to torsion only, find the diameter of the shafts and pins. The allowable shear stresses for the shaft and pin may be taken as 60MPa and 28MPa respectively.
Q.19 Design a square key for fixing a gear on the shaft having 25mm diameter. The gear rotates at
550rpm and transmits 12kW power to the meshing gear. The key is made of steel having yield stress in tension as 400N/mm2. The yield stress in compression and tension may be taken equal to each other.
Assume factor of safety 2.5.
Q.20 Design a clamp coupling to transmit 30kW at 100rpm. The allowable shear stress for the shaft and key is 40MPa and number of bolts connecting the two halves are six. The permissible tensile stress for e coefficient of friction between the muff and the shaft surface may be taken as 0.3.