Machine Design (MD)

Q:   If the wire diameter of a compressive helical spring is increased by 2%, the change in spring stiffness (in %) is _____ (correct to two decimal places).

Q:   A self-aligning ball bearing has a basic dynamic load rating (C10, for 10⁶ revolutions) of 35 kN. If the equivalent radial load on the bearing is 45 kN, the expected life (in 10⁶ revolutions) is

• A:  below 0.5
• B:  0.5 to 0.8
• C:  0.8 to 1.0
• D:  above 1.0

Q:   Pre-tensioning of a bolted joint is used to

• A:  strain harden the bolt head
• B:  decrease stiffness of the bolted joint
• C:  increase stiffness of the bolted joint
• D:  prevent yielding of the thread root

Q:   A bar is subjected to a combination of a steady load of 60 kN and a load fluctuating between -10 kN and 90 kN. The corrected endurance limit of the bar is 150 MPa, the yield strength of the material is 480 MPa and the ultimate strength of the material is 600 MPa. The bar cross-section is square with side a. If the factor of safety is 2, the value of a (in mm), according to the modified Goodman’s criterion, is ________ (correct to two decimal places).

Q:   A motor driving a solid circulr steel shaft transmits 40 kW of power at 500 rpm. If the diameter of the shaft is 400 mm, the maximum shear stress in the shaft is _________ MPa.

Q:   Consider the schematic of a riveted lap joint subjected to tensile load F , as shown below. Let d be the diameter of the rivets, and Sf be the maximum permissible tensile stress in the plates. What should be the minimum value for the thickness of the plates to guard against tensile failure of the plates? Assume the plates to be identical.

• A:  F/[S_f(W−2d)]
• B:  F/[S_fW]
• C:  F/[S_f(W−d)]
• D:  2F/[S_fW]

Q:   A machine component made of a ductile material is subject to a variable loading with σ_min=−50 MPa and σ_max=50 MPa. If the corrected endurance limit and the yield strength for the material are σ′_e =100 MPa and σ_y=300 MPa, respectively, the factor of safety is___________

Q:   A helical compression spring made of a wire of circular cross-section is subjected to a compressive load. The maximum shear stress induced in the cross-section of the wire is 24 MPa. For the same compressive load, if both the wire diameter and the mean coil diameter are doubled, the maximum shear stress (in MPa) induced in the cross-section of the wire is___________

Q:   A single-plate clutch has a friction disc with inner and outer radii of 20 mm and 40 mm, respectively. The friction lining in the disc is made in such a way that the coefficient of friction μ various radially as μ=0.01r . Where r is in mm. The clutch needs to transmit a friction torque of 18.85 kN mm. As per uniform pressure theory, the pressure (in MPa) on the disc is___________

Q:   The principal stresses at a point inside a solid object are σ₁=100MPa σ₂=100MPa and σ₃=0MPa. The yield strength of the material is 200 MPa. The factor of safety calculated using Tresca (maximum shear stress) theory is n_T and the factor of safety calculated using von Mises (maximum distortional energy) theory is n_V. Which one of the following relations is TRUE?

• A:  n_T=√(3/2)n_V
• B:  n_T=√(3)n_V
• C:  n_T=n_V
• D:  n_V=√(3)n_T