Top mechanical engineering interview questions with short answers for production, maintenance and design jobs.
1. What is the difference between stress and strain?
Stress is the internal force per unit area in a material (unit N/mm²). Strain is the change in length divided by the original length; it has no unit.
2. State Hooke’s law.
Within the elastic limit, stress is directly proportional to strain. The constant of proportionality is the modulus of elasticity (Young’s modulus).
3. What is cavitation in a pump?
When the pressure at the pump inlet falls below the vapour pressure of the liquid, vapour bubbles form and collapse violently. This causes noise, vibration and damage to the impeller. Enough NPSH (net positive suction head) prevents it.
4. What is the difference between a pump and a compressor?
A pump moves liquids, which are nearly incompressible. A compressor increases the pressure of gases by reducing their volume.
5. What is the difference between the Otto and Diesel cycles?
In the Otto cycle (petrol engine), heat is added at constant volume and the fuel is ignited by a spark. In the Diesel cycle, heat is added at constant pressure and the fuel ignites due to the high temperature of compressed air.
6. Name common types of bearings.
Ball bearings, roller bearings (cylindrical, tapered, spherical), needle bearings, thrust bearings and plain (journal) bearings.
7. What are annealing, hardening and tempering?
Annealing softens steel and removes internal stress by slow cooling. Hardening increases hardness by heating and quick quenching. Tempering reduces the brittleness of hardened steel by reheating to a lower temperature.
8. What is the difference between tolerance and allowance?
Tolerance is the permitted variation in the size of one part. Allowance is the intended difference between the sizes of two mating parts, such as a shaft and a hole.
9. What is the difference between boiler mountings and accessories?
Mountings are fitted for safety and control, such as the safety valve, water level indicator and pressure gauge. Accessories improve efficiency, such as the economiser, superheater and air pre-heater.
10. Name common welding processes.
Shielded metal arc welding (SMAW/stick), MIG (GMAW), TIG (GTAW), submerged arc welding, gas welding and spot (resistance) welding.
These are common questions asked in interviews for freshers and experienced candidates. Read each topic in your textbook for full details. See the latest jobs on our homepage.