JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III DESIGN OF MACHINE MEMBERS - I Previous Question Paper (August - 2022 - R18)

Using the Indian Standard (IS) system of limits and fits, the dimensions are determined based on the recommended fit for each application:

1. 12 mm electric motor sleeve bearing: Requires a running fit, typically H7/f6. For a 12 mm nominal diameter, the hole (H7) is 12.000 to 12.018 mm and the shaft (f6) is 11.984 to 11.995 mm.
2. 200 mm medium force fit: Requires a transition or interference fit, typically H7/s6. For a 200 mm nominal diameter, the hole (H7) is 200.000 to 200.046 mm and the shaft (s6) is 200.072 to 200.101 mm.
3. 50 mm sleeve bearing (road grader): Requires a clearance fit for heavy-duty operation, typically H8/e8. For a 50 mm nominal diameter, the hole (H8) is 50.000 to 50.039 mm and the shaft (e8) is 49.920 to 49.959 mm.

Mechanical components fail due to various modes depending on material properties, loading conditions, and geometric constraints:

1. Elastic Deflection: Occurs when a component deforms beyond functional limits without permanent damage. Examples include machine tool spindles, precision shafts, and leaf springs where stiffness is critical to maintain alignment or accuracy.
2. General Yielding: Occurs when the stress exceeds the yield strength of a ductile material, leading to permanent deformation. Examples include bolts tightened beyond their elastic limit, structural beams overloaded in bending, and pressure vessels subjected to excessive internal pressure.
3. Fracture: Occurs when a component separates into two or more pieces, often due to brittle failure or fatigue crack propagation. Examples include cast iron machine bases (brittle fracture), turbine blades subjected to cyclic thermal stress (fatigue fracture), and high-strength steel shafts under sudden impact loads.