JNTU
JNTU B.Tech III DESIGN OF MACHINE MEMBERS I Previous Question Paper (February - 2022 - R13)
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Main
What is the hole-basis system for giving tolerances?
Answer
In the hole-basis system, the fundamental deviation of the hole is fixed as zero, meaning the lower limit of the hole is equal to the basic size. The required fit between the hole and the shaft is achieved by varying the size of the shaft. This system is preferred in manufacturing because it is easier to produce a variety of shaft sizes to fit a standard hole using standard reamers or broaches.
A shaft is loaded by a torque of 5 kN-m. The material has a yield point of 350 MPa. Find the required diameter of shaft using (i) Maximum shear stress theory, (ii) Maximum distortion energy theory. Take a factor of safety of 2.5.
Answer
Given: Torque (T) = 5 kN-m = 5 x 106 N-mm; Yield strength (σy) = 350 MPa; Factor of safety (FOS) = 2.5.
The allowable shear stress (τ) is calculated as:
The relationship between torque and diameter (d) is given by:
Substituting the values:
(i) Maximum Shear Stress Theory (Guest's Theory): The design shear stress is 70 MPa, resulting in a required diameter of approximately 71.4 mm.
(ii) Maximum Distortion Energy Theory (von Mises Theory): The yield strength in shear (τy) is σy / √3. The allowable shear stress is τ = σy / (√3 × FOS) = 350 / (1.732 × 2.5) ≈ 80.83 MPa. Substituting into the torque equation:
Define factor of safety for fatigue loading.
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Find the diameter of a shaft to transmit twisting moment varying from 800 N-m to 1200 N-m. The ultimate tensile strength for the material is 600 MPa and yield stress is 450 MPa. Assume the stress concentration factor=1.2, surface finish factor=0.8 and size factor=0.85.
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A steel plate, 80 mm wide and 10 mm thick, is joined to another steel plate by means of a single transverse and double parallel fillet welds. The strength of the welded joint should be equal to the strength of the plates to be joined. The permissible tensile and shear stresses for the weld material and the plates are 100 and 70 N/mm2 respectively. Find the length of each parallel fillet weld. Assume that the tensile force passes through the center of gravity of three welds.
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How is the strength of transverse fillet weld evaluated?
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A double-riveted double-strap butt joint is used to connect two plates, each of 12 mm thickness, by means of 16 mm diameter rivets having a pitch of 48 mm. The rivets and plates are made of steel. The permissible stresses in tension, shear and compression are 80, 60 and 120 N/mm2 respectively. Determine the efficiency of the joint.
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It is required to design a knuckle joint to connect circular shafts subjected to an axial force of 50 kN. The rods are coaxial and a small amount of angular movement between their axes is permissible. Design the joint and specify the dimensions of its components on a neat sketch. The allowable tensile, compressive and shear stress in the rod and pin material is limited to 80 MPa, 100 MPa, and 40 MPa respectively.
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Distinguish between feather key, flat key, and woodruff key? Give their applications.
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The cross-section of a flat key for a 40 mm diameter shaft is 22 × 14 mm. The power transmitted by the shaft to the hub is 25 kW at 300 rpm. The key is made of steel (Syc = Syt = 300 N/mm2) and the factor of safety is 2.8. Determine the length of the key. Assume (Ssy = 0.577 Syt).
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A steel solid shaft transmitting 15 kW at 200 rpm is supported on two bearings 750 mm apart and has two gears keyed to it. The pinion having 30 teeth of 5 mm module is located 100 mm to the left of the right hand bearing and delivers power horizontally to the right. The gear having 100 teeth of 5 mm module is located 150 mm to the right of the left hand bearing and receives power in a vertical direction from below. Using an allowable stress of 55 MN/m2 in shear, determine the diameter of the shaft.
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Design a helical spring for a spring loaded safety valve for the following conditions: Diameter of valve seat = 65 mm, operating pressure = 0.7 N/mm2, Maximum pressure when the valve blows off freely = 0.75 N/mm2, Maximum lift of the valve when the pressure rises from 0.7 to 0.75 N/mm2 = 3.5 mm, Maximum allowable stress = 550 MPa, Modulus of rigidity = 84 KN/mm2, Spring index = 6.
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What are the objectives of series and parallel connections of springs?
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