Mechanical Engineering Interview Questions with Answers

Interview Questions with Answers on Mechanical Design, Strength of Materials, Kinematics of Machine, Manufacturing Process, Engineering Mechanics & Mechanical Vibrations: Set 02

Question No. 51
Why I-section beam is preferred for heavy loading?
Cross sectional shape I, giving many benefits. It is very good for giving stiffness (less deformation on loading) and to withstand higher bending moments (as a result of heavy loading) on comparison with other cross-sectional shapes of same area. Also, it is very easy to manufacture. It will have more moment of inertia.

Question No. 52
What is difference between Center of Mass and Center of Gravity?
Both terms are same when gravity is uniform. When gravity is non-uniform following are the terms:
The centre of mass is a point that acts as if all the mass was centered there (the mass on one side of the point is equal to the mass on the opposite side). If supported at the centre of mass, an object will be balanced under the influence of gravity.
The centre of gravity is the point at which where the sum (vector) of the gravitational forces act on an object which will be balanced on that point.

Question No. 53
What are the differences between Weight and Mass?
Mass is a measure of how much matter an object has. Mass is specified in Gram or Kilograms.
Weight is a measure of how strongly gravity pulls on that matter. Force is measured in Newton’s.
Thus if you were to travel to the moon your weight would change because the pull of gravity is weaker there than on Earth but, your mass would stay the same because you are still made up of the same amount of matter.

Question No. 54
What is the difference between Projectile motion and a Rocket motion?
A projectile has no motor/rocket on it, so all of its momentum is given to it as it is launched. An example of a projectile would be pen that you throw across a room.
A rocket or missile does have a motor/rocket on it so it can accelerate itself while moving and so resist other forces such as gravity. In mechanics point of view projectile don’t have any particular shape it is a point mass. Whereas rocket has a particular shape and hence it has centre of gravity situated at particular point on its body. Therefore rocket motion comes under kinetics and projectile comes under kinematics.

Question No. 55
What type of cooling used in High Voltage Transformer?
The big transformers you find on power poles usually use oil as a dielectric insulator, in smaller HV transformers, like the ones in TV’s are usually filled with resin.

Question No. 56
What is honing of Cylinder Liners?
The honing equipment used has been manufactured by "Chris Marine". The head of the honing device consists of four synchronized stones. For the initial honing diamond stones are used to break up the hardened surface in the scuffed areas. For the main honing very coarse and hard stones are used to produce a very desirable rough surface all over the liner. The advantage, especially for the 2-stroke engines, is possibility to save the liner after a seizure, scuffing or blow-by or even to eliminate the ovality of the liner. Another advantage is that it is possible to machine a rough liner wall to obtain a well oiled surface.

Question No. 57
What is the difference between Speed and Velocity?
Speed is scalar quantity and Velocity is a vector.
Velocity has both speed and direction. Speed is expressed as distance moved (d) per unit of time (t). Speed is measured in the same physical units of measurement as velocity, but does not contain an element of direction. Speed is thus the magnitude component of velocity.

Question No. 58
Difference between Yield Stress and Yield Strength?
Stress is a measure of the load applied to a sample relative to a cross sectional area of the sample. Strength is a quantification of the samples ability to carry a load.
The terms "yield strength" and "yield stress" of a material are usually used interchangeably (correct or not). It is the stress which will just cause the material to plastically deform. If a material yields at
30,000 psi, the yield stress is 30,000 psi. If the part in question has a cross sectional area of 2 square inches, the strength at yield would be 60,000 pounds, but usually we just say the yield strength is 30,000 psi.

Question No. 59
What is the difference between Yield and Ultimate tensile strength?
The yield strength is reached when the material becomes Non – linear (that is non elastic) and takes a permanent set when load is released. Material stretches but does not break. Ultimate strength is when it breaks and is higher than yield strength.

Question No. 60
What is the difference between Flexural strength and Tensile strength?
Flexural strength is resistance offered against bending. Tensile strength is resistance offered against tensile force.

Question No. 61
What is the difference between Shear and Tensile strength?
Tensile Strength for a Bolt is determined by applying a Force along it long axis. Shear
Strength for a Bolt is determined by applying a Force across its diameter, as it would be loaded in a lug joint. Tensile strength is strength in tension when pulling force is applied. And shear strength is strength against cutting force which is known as shear force.

Question No. 62
What is the difference between Tensile strength and tensile modulus?
Tensile strength is the ultimate capacity of the material to resist a tensile load regardless of deflection.
Tensile modulus also known as Young’s modulus is a measure of the stiffness of an isotropic elastic material. It is defined as the ratio of the uni-axial stress over the uni-axial strain. It is determined from the slope of a stress-strain curve traced during tensile tests conducted on a sample of the material.

Question No. 63
What is OEE?
OEE means Overall Equipment Effectiveness.
This terminology widely used in Total productive maintenance, which is used to calculate the effectiveness of machines in manufacturing. Basically it captures the losses of machines in production and tries to improve defects on machines. Higher the OEE, more capable is the machine.

Question No. 64
Why Involutes Curve used in Gear?
Involute curve is the path traced by a point on a line as the line rolls without slipping on the circumference of a circle. Involute curve has a contact angle between two gears when the tangents of two gears pass through the contact point without friction.

Question No. 65
What is bearing stress?
The stress which acts on the contact surface area between two members is known as bearing stress. An example for this is the stress between nut and the washer

Question No. 66
Which is hard material Cast Iron or Mild Steel?
Cast iron. Due to the excess carbon content than mild steel it is harder. The more carbon content, the more hardness will be. But it reduces the Weldability due to this hardness.
It is brittle too.

Question No. 67
What are the materials used for Sliding Wear pad?
  1. Urethane-Coated Base Material Provides Optimum Sliding Surfaces for Maximum Wear Ability.
  2. Galvanized Steel for Backing on Head and Side Pads.
  3. For crane services, we use Velcro Nylon wearing pad
Question No. 68
What is the difference between a Shaper machine and a Planner machine?
In Shaper machine tool is having reciprocating motion and work piece is clamped on table which is stationary. It is mostly suitable for light duty operation. In Shaping large cutting force is transferred to tool. In Planer machine tool is having stationary and work piece is clamped on table which is reciprocating motion. It is mostly suitable for Heavy duty operation. In planner large cutting force is transferred to table.

Question No. 69
How will you calculate the tonnage of Mechanical Press?
F = (S × L × T)/ 1000
F = Force in kilo Newton’s
S = shear stress of material in MPa
L = the total length of peripheries being cut/ sheared in mm T = thickness of material in mm

Question No. 70
What is the composition of Grey cast iron Grade 20?
Carbon: 3.10 – 3.25%, Silicon: 1.75 – 1.95%, Manganese: 0.50 – 0.7%, Sulphur: 0.05 – 0.07%, Phosphorous: 0.04 – 0.07%

Question No. 71
What is the composition of Cast iron Grade 35?
Carbon=2.90 – 3.10%, Manganese=0.60 – 1.00%, Silicon=1.50 – 1.90%, Sulphur=0.10%, Phosphorus=0.15%, Chromium=0.30%, Molybdenum=0.30%, Cupper=0.25%

Question No. 72
What are the super alloys?
Super alloys are an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, having good surface finish.

Question No. 73
Why the Super alloys used for land based turbines?
Super alloys are the top most alloys used for their excellent strength and corrosion resistance as well as oxidation resistance. No other alloys can compete with these grades.

Question No. 74
What kinds of NDT methods are available?
  1. Visual Inspection
  2. Microscopy inspection
  3. Radiography Test
  4. Dye Penetrate technique
  5. Ultrasonic testing
  6. Magnetic Particle inspection
  7. Eddy Current technology
  8. Acoustic Emission
  9. Thermograph
  10. Replica Metallographic
Question No. 75
What is Stress Corrosion cracking?
Stress corrosion cracking (SCC) is a process involving the initiation of cracks and their propagation, possibly up to complete failure of a component, due to the combined action of tensile mechanical loading and a corrosive medium.

Question No. 76
What is meant by D2 Material used for Die tooling?
D2 – High Carbon Cold Work Tool Steel.
D2 is a high Carbon, high Chromium, Molybdenum, Vanadium, Air hardening alloy tool steel which offers good wear resistance, high surface hardness, through hardening properties, dimensional stability and high resistance to tempering effect. D2 tool steel is also suitable for vacuum hardening.
Typical Composition:
C. = 1.50%, Si. = 0.30%, Cr. = 12.00%, Mo. = 0.80%, V. = 0.90%

Question No. 77
What is Vacuum Induction Melting?
As the name suggests, the process involves melting of a metal under vacuum conditions. Electromagnetic induction is used as the energy source for melting the metal. Induction melting works by inducing electrical eddy currents in the metal. The source is the induction coil which carries an alternating current. The eddy currents heat and eventually melt the charge.

Question No. 78
What is the difference between Bolt and Screw?
The main difference was based on the load acting on it, and the size. For smaller loads, screws are enough but in case of greater-loads, bolts are to be used. In bolt we give centrifugal force or tangential force and screw we give axial force for driving.

Question No. 79
What is the function of a thrust bearing?
Thrust bearings keep the rotor in its correct axial position.

Question No. 80
What is the significance of Torque (in N-m) given in the engine specification?
It give the moment about any point or simple rotation.

Question No. 81
What are the uses of Graphite electrode in various fields?
Graphite electrode is used in EDM and in battery cells. It is also used in electric arc furnaces to melt the steel.

Question No. 82
Difference between TIG & MIG welding
TIG - Tungsten inert gas welding-non consumable electrode
MIG - Metal inert gas welding-uses consumable electrode

Question No. 83
Do you know epicyclic gear box? What is the practical application of epicyclic gear box?
Epicyclic gear box consists of sun gear planetary gears and an annular called ring gear. Different speed ratios are obtained by locking any one gear. If you lock any two gears, direct gear will be obtained. Mostly used in over drives.
Wrist watch is a practical application of epicyclic gear box

Question No. 84
What is the purpose of scrapper ring?
Scrap the excess lube oil from the cylinder walls. There by preventing oil from entering combustion zone.

Question No. 85
What is the difference between S.S to EN8?
SS- Stainless steel
En- Medium carbon steel
SS is Non Magnetic material & EN8 is Magnetic material
SS is Corrosion resistant & EN8 is Magnetic material

Question No. 86
How to calculate the speed of conveyor in Meter per Minute
Measure the diameter of the rollers around which the conveyor belt is wrapped.
Multiply the diameter of the roller by pi (3.14159). This calculation will yield the circumference of the rollers. Every time the roller spins one revolution, the conveyor will be moved a linear distance equivalent to the circumference of the roller. Pi is a dimensionless factor, meaning it does not matter whether inches, centimeters or any other units of measurement are used. Measure the revolutions per minute (RPM) of the rollers. Count how many full revolutions (rotations) are made by the roller in one minute. Multiply the RPM by the circumference of the roller. This calculation will give the linear distance traversed by a point on the conveyor belt in one minute.

Question No. 87
What is the use of a PULLEY?
Transmission of power (force) in rotary form

Question No. 88
Why does cycle rim don’t bend even in heavy loads?
Because of rubber tires. The load is distributed and its effect reduces i.e. tires absorbs heavy load and shocks with the support of steel rim. The rim has many spokes. The spokes distribute the load equally and the rubber tires absorb more than half of the load.

Question No. 89
What is caustic embrittlement?
It is the actual physical change in metal that makes it extremely brittle and filled with minute cracks. It occurs particularly in the seams of riveted joints and around the rivet holes.

Question No. 90
What type of section of same area will resist maximum bending moment, I section, rectangular or circular section?
I- section of same area resist more bending moment than a rectangular or circular section. The reason is obvious. In i-section larger area is concentrated at larger distance from neutral axis and hence stressed more.
In circular section, large area is concentrated near neutral axis and hence it is inefficient in resisting bending.
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