Design of Machine Elements - short answer questions from AMIE exams (Winter 2025)
What are the causes and effects of stress concentration?
Stress concentration is the localized increase in stress that occurs where a material's geometry changes abruptly—such as at holes, notches, fillets, grooves, or sharp corners.
Causes of Stress Concentration
Stress concentration is almost always caused by a discontinuity or abrupt change in geometry that interrupts the smooth flow of stress.
Common causes include:
- Holes and Openings
- Sharp Corners and Notches
- Fillets with Small Radi
- Grooves and Keyways
- Threads
- Inclusions and Internal Defects
- Sudden Changes in Cross-Sectio
- Surface Roughness and Machining Marks
Effects of Stress Concentration
The primary effect is that local stress can be many times higher than the nominal stress, which can lead to:
- Reduced Static Strength
- Fatigue Failure
- Crack Initiation and Propagation
- Reduced Load Capacity
- Brittle Fracture in Normally Ductile Materials
- Warping or Local Yielding
What arc the advantages and disadvantages (at least three in each) of welded joints when it is compared with bolted joints?
Advantages of Welded Joints
- Stronger and More Rigid Connection
- Lighter Weight and Material Savings
- Better Sealing and Leak-Proofness
Disadvantages of Welded Joints
- Permanent Joint — Difficult to Disassemble
- Susceptible to Defects and Quality Issues
- Residual Stresses and Distortion
What is nipping in leaf spring and state its purpose?
Nipping in a leaf spring refers to the pre-stressing process in which the individual leaves (plates) of a semi-elliptical or similar leaf spring are initially curved to different radii before assembly. When these leaves are clamped together by the central bolt, they are forced to conform to a common curvature. This deliberate mismatch in curvature creates a built-in stress distribution across the spring.
What is the meaning of self-acting bearing? What are its advantages?
A self-acting bearing is a type of fluid bearing that generates its own supporting pressure through the relative motion of its surfaces. This means it does not require an external pump or pressurized fluid supply to operate.
Self-acting bearings offer several distinct benefits over other bearing types:
- Simplicity and Cost:
- Zero Wear During Operation
- High Stability
- Oil-Free and Clean Operation
- Precise Running Accuracy
What is the function of a clutch and list out the design theories related with clutches?
A clutch is a mechanical device that connects and disconnects rotating shafts, allowing a vehicle's engine to be temporarily separated from the transmission for gear changes and to gradually take up drive from a standstill.
Several engineering theories and principles guide the design of clutches
- Friction and Wear Theory
- Thermal Analysis
- Torsional Vibration and Damping
- Geometric and Multi-Stage Engagement Design
- Hydraulic and Lubrication Theory
What is the difference between a fly wheel and a governor?
A flywheel is a heavy rotating wheel that stores kinetic energy. During the power stroke, it absorbs excess energy; during the other strokes (intake, compression, exhaust), it releases that energy to keep the crankshaft turning smoothly.
A governor continuously senses the engine's speed and automatically adjusts the fuel or steam supply to keep the speed constant, even when the load changes.
What are distinctive applications of Oldham's coupling and universal coupling?
Oldham couplings and universal couplings are both used to transmit torque between misaligned shafts, but their distinctive applications stem from how they handle misalignment.
Oldham couplings excel at parallel misalignment while maintaining constant velocity, whereas universal couplings are designed for angular misalignment and are workhorses for high-torque, variable-angle power transmission.
What is the meaning interference in gear transmission and list out its causes and consequences?
In gear transmission, interference refers to the condition where the tip of a gear tooth (usually the dedendum or addendum of one gear) digs into or clashes with the non-involute portion of the mating gear tooth, typically near the root.
Cause of Interference
- Too Few Teeth on Pinion
- Large Addendum on Mating Gear
- Small Pressure Angle
- Large Gear Ratio
What arc the advantages of a rolling contact bearing over a sliding contact bearing. What does the bearing designation "6309" mean?
Advantages of Rolling Contact Bearings vs. Sliding Contact Bearings
- Lower Friction and Starting Torque
- Higher Precision and Interchangeability
- Simpler Lubrication and Maintenance
- Better Performance at Low and Medium Speeds
- Compact Design
The designation 6309 is a standard ISO bearing number for a single-row deep groove ball bearing.
6 is Type Code: Indicates a single-row deep groove ball bearing.
3 is Dimension Series: Indicates the width and diameter series (medium duty).
09 is Bore Size Code: When multiplied by 5, this gives the bore diameter in millimeters. So, 09 × 5 = 45 mm
What is the expansion of BIS? Is BIS certification mandatory for all products? Which IS code providing the specification of general-purpose structural steel?
BIS stands for the Bureau of Indian Standards.
No, BIS certification is not mandatory for all products. The certification scheme is voluntary in nature by default .
The Indian Standard that provides the specification for general-purpose structural steel is: IS 2062 — Hot Rolled Medium and High Tensile Structural Steel — Specification.
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