Mechanical Engineering Interview Questions And Answers

Mechanical engineering is a covering all different area of engineering. Mechanical engineering is the discipline that applies the principles of engineering, physics, and materials science for the design, analysis, manufacturing, and maintenance of mechanical systems. It is the branch of engineering that involves the design, production, and operation of machinery. It is one of the oldest and broadest of the engineering disciplines. The mechanical engineering field requires an understanding of core areas including mechanics, kinematics, thermodynamics, materials science, structural analysis, and electricity.

Mechanical engineers use these core principles along with tools like computer-aided design, and product lifecycle management to design and analyze manufacturing plants, industrial equipment and machinery, heating and cooling systems, transport systems, aircraft, watercraft, robotics, medical devices, weapons, and others. They may create power-producing and power-using machinery, including gas turbines, industrial equipment for manufacturing and electric generators.

Mechanical engineers must provide engineering designing and guidance alongside other team members to develop better and more advanced ways of production of an object or tool. Also, they must be able to solve complex problems where analysis of a situation and data in-depth evaluation are required in order to meet the requirement of the customer.

Mechanical engineers must as well be able to work with other engineers and production personnel not to only develop but also to maintain the manufacturing process. Also, this type of engineer as well as any other kind of engineer must be able to prepare and present technical status reviews to show its customers overall improvement of a give task or project. Interface with development engineers, scientists and suppliers to resolve quality issues. Conduct engineering tasks and work efficiently.

Mechanical engineers should be creative, inquisitive, analytical, and detail oriented. They should be able to work as part of a team and communicate well in both writing and orally since mechanical engineers must interact with a broad array of specialists in a wide range of fields inside as well as inside the engineering field. Also, since mechanical engineers may also work on manufacturing and agriculture production they might later become administrators or managers.

• Power-producing machines such as electric generators, internal combustion engines, and steam and gas turbines
• Power-using machines, such as refrigeration and air-conditioning
• Industrial production equipment, including robots used in manufacturing
• Other machines inside buildings, such as elevators and escalators
• Machine tools and tools for other engineers
• Material-handling systems, such as conveyor systems and automated transfer stations

A mechanism is an assembly of different parts which perform a complete motion and is often part of a machine.

Thermostat ensures optimum cooling because excessive cooling decreases the overall efficiency. It allowed cooling water to go to radiator beyond a predetermined temperature.

Thermostats are used in device are system that heats are cools to a set point temperature. The thermostat regulates the temperature of the engine.

When it is fully open the coolant flows from the engine block to the radiator and to maintain temperature when its closed the circuit to the radiator is off. It’s usually located in the upper section of the engine block

Scavenging is the process of flushing out burnt gases from engine cylinder by introducing fresh air in the cylinder before exhaust stroke ends.

Supercharging is the process of supplying higher mass of air by compressing the atmospheric air.

The main differing between this supercharger and turbocharger is lies in its power supply. Supercharger will take its power from the crankshaft and the turbocharger will draw power from exhaust gases that result from combustion.

Extrusion is the process where a metal or a metal bar is pulled through a mandrel to elongate it and/or give it a final shape. Extruded Aluminum is a common form of making small aluminum wire, bars or beams and many varieties of small non-structural, decorative pieces.

Torque is also called as the moment of force. And the torque is the force that causes rotation. Torque is a measure of how much force is acting on an object making it rotate. The symbol of the torque is T

T= r × F

If we use the petrol in diesel engine, there won’t be smooth combustion rather detonation that may lead engine damage.

The tyres are black due to the carbon content.

The compress ratio of diesel engine is higher than the petrol engine, because it’s producing higher torque. The efficiency of diesel engine increases with load. Diesel produce a slow energy on burning of fuel and efficiency of engine increases with load that’s why diesel engine is suitable and a largely used for heavy vehicles.

Slenderness ratio is the ratio of the length of a column and least radius of gyration of its cross section.

According to Bauschinger, the limit of proportionality of material does not remain constant but varies according to the direction of stress under cyclic stresses

Torsional rigidity or stiffness of shaft is defined as the product of modulus of rigidity (C) and the polar moment of inertia of the shaft (J). The torsional rigidity is given by

  Torsional rigidity = C×J.

Torsional rigidity is also defined as the torque required producing a twist of one radiant per unit length of shaft.

Shear stress acts parallel to the plane of the cross section of beam. Shear stress varies parabolically over the depth of beam. At the extreme fibre shear stress is zero. At neutral axis shear stress have some value.

Bending stress acts perpendicular to the plane of cross section. Bending stress varies linearly over the depth of beam. At extreme fibre bending stress is maximum. At neutral axis bending stress is zero.

The total entropy of the universe increases over time and moves towards a maximum value.

Cotter joints are used to connect the two rods, which are under compressive or tensile stress. The ends of the rods are in manner of a socket and shaft that fit together and the cotter is driven into a slot that is common to both pieces drawing them tightly together.

The tensile strength of the steel is proportional to the strength needed to offset the stress of the material divided by the number of the joints employed.

The tin and the lead alloy are commonly called solder. The solder is a wire with a rosin core used for soldering.  The tin and the lead is used to create the electrical joints. Tense plate is an alloy of tin and lead used to coat steel. Some antique pewter contains both the tin and lead, sometimes in combination of other metals.

Otto cycle is an idealized thermodynamic cycle. The Otto cycle is a set of processes used by spark ignition internal combustion engines (2-stroke or 4- stroke cycles). The cycle starts with an intake stroke, closing intake and moving to the compressive stroke, starting of combustion, power stroke, heat exchange stroke where heat is rejected and the exhaust stroke. Otto cycle was designed by Nicolas Otto, a German engineer.

Gear ratio is the ratio of the number of revolutions of the opinion gear to one revolution of the idler gear

It is a process of heating a material above the re-crystallization temperature and cooling after a specific time interval. This increases the hardness and strength if the material.

Uniformly distributed load is a distributed load which has a constant value such as 1KN/m. Or it is also defined as the force applied over an area per unit length. This load is spread across a region of the beam.

Pneumatic is confined pressurized systems that use moving air or other gases, because gases can be compressed there is a delay in the movement, force. The examples of pneumatic are precision drills used by dentists, pneumatic brakes (air brakes) used by buses, trucks, trains, and also used in lungs, nail gun, dentist chair.

Hydraulics is confined pressurized systems that use moving liquids. Liquids are not very compressible; there is no delay in the movement. Examples of the hydraulics are dump truck lift, hydraulic lift to lift cars, jaws of lift, blood in body, used in cars, etc.

Enthalpy is the heat content of a chemical system.

Advantages of gear drives are:

• It transmits exact velocity ratio.
• High transmission efficiency.
• Used for low, medium, and high-power transmission.
• It may be used for small center distance of shafts.
• It has reliable service.
• Unlike belt drives, spur gear drives have no slip.
• They are compact and easy to install.

A Newtonian fluid possesses a linear stress strain relationship curve. And the curve is passes through the origin. The fluid properties of Newtonian fluid do not change when any force acts upon it.

The two-stroke engine have very high to be compared to the four stroke engine. Because the power stroke is generated every two revolutions while in four stroke, power stroke is gendered every four revolutions.

CC means cubic centimeter. And it represents the total volume of the engine cylinder. This reflects that the engines with more CC can generate more powers than the other engines. CC can also be related as inversely proportional to fuel consumption.

The most efficient shape for withstanding high pressure is a sphere but that is costly to manufacture.  A cylinder is having a dumped top and Dumped bottom (look underneath, the flat base is actually welded around the outside, the bottom of the gas container is actually dumped) is a much cheaper shape to manufacture whist. And it is having the good strengths to resist the internal gas pressure.

The points in the stress strain curve in steel are:

• Proportional limit
• Elastic limit or yield point
• Ultimate stress
• Stress at failure.

Nitrogen is used to prevent porosity in the welding member by preventing oxygen and air from entering the molten metal during the welding process. Other gasses are also used for this purpose such as Argon, Helium, Carbon Dioxide, and the gasses are given off when the flux burns away during SMAW (stick) welding.

Steam is a compressible gas due to which the capacity of the pipe line depends on the size of the pipes and pressure of the steam. Since steam at even low pressure can be dangerous, extra care is to be taken. Galvanized pipes are usually not used for steam. Pipes made of mild steel with welded fittings are instead largely used.

It is the phase at which the natural frequency of the turbine shaft matches with the frequency at the speed. During this period more vibration will come. To avoid this acceleration will be increased so that times to cross the critical speed.

Ferrite: solid solution of carbon in BCC iron from room temperature to 9100C. Maximum solubility of carbon is 0.022% at temperature of 7270C. And it is also called as alpha ferrite.

Austenite: solid solution of carbon in FCC iron also called as gamma iron. It exists from 910-13950C. Toughest phase among all strength along with optimum ductility.

Stellite is a nonferrous cast alloy containing cobalt, chromium and tungsten.

Car tyres are usually made of styrene-butadiene rubber.

Brass is an alloy of copper with zinc. And bronze is an alloy of copper with tin.

• Boiler tubes usually made from carbon steel. And the boiler tubes are subjected to.
• High rates of heat transfer.
• Bending stresses due to uneven heating, especially at expanded or welded joints into headers or drums.
• External erosion from burners and flue gas.
• Possible corrosion on the boiler side.
• Occasional manufacturing defects.

Failure may occur due to following reasons:

• High thermal ratings may lead to rapid failure if the internal fluid flow is reduced for any reason. The resultant overheating leads to a failure by creep, characterized by the bulging of the tube with the eventual development of a longitudinal split.
• Fatigue cracking due to bending stresses occurs. These are associated with change of section and/or weld undercut, where tubes are expended or welded into headers
• Failure may arise due to overstressing of a reduced section of metal.
• Sudden failure of the boiler tube due to corrosion arises from embrittlement of the carbon steel due to interaction between atomic hydrogen from the corrosion process and the iron carbide present in the steel.
• Defects in the tube manufacture, although far from being a regular occurrence, can be a cause of serious trouble. Lamination in boiler tubers score marks arising from the cold drawing of tubes give arise to premature failure and may promote corrosion at these regions.

Superheated tubes are subjected to the most severe combination of stress, and corrosive environment. In addition to high temperature strength, resistance to corrosion is also important. For example, low_ alloy ferrite steel such as -1% cr,1% Mo would not be used at metal temperatures above 5800C because of inadequate resistance to corrosion and oxidation over a full-service life of 100,000/150,000 hr.

• Failures in superheated tubes may arise form:
• Prior fabrication history.
• Faulty heat treatment.
• Consequences of welding.
• Overheating of the tube metal.
• Gas-side corrosion.
• Stress corrosion (austenitic steels).

Coal is a flammable black hard rock used as a solid fossil fuel. Coal is made of 65-95% carbon and also contains hydrogen, Sulphur, oxygen and nitrogen. Coal is one of the world’s major sources of energy. Coal is used to produce nearly half of all the electric energy that is generated and used in the unit.

Fuel ratio is the ratio of its percentage of fixed carbon to volatile matter.

Isotropic material means a material having identical values of a property in all directions. Glass and metals are examples of isotropic materials.

Anisotropic material properties such as young’s modulus, change with direction along the object. The examples of the anisotropic materials are wood and composites. Anisotropic is a directionally at a single point property vary with direction.

Isotropy and anisotropy. can be distinguished based on stiffness matrix.

If the material has three mutually orthogonal planes of electric symmetry is called orthotropic materials. They are a subset of anisotropic materials, because their properties change when measured from different directions. The example of orthotropic material is wood.

COP of heating is one (unity) more than COP of cooling.

Pitting is the non-uniform corrosion over the entire metal surface but occurring only in small pits. And pitting is caused by lack of uniformity in metal.

Elliptical shape has minimum area of opening and thus plate is weakened the least. Further it is very convenient to insert and take out the cover plate from elliptical opening.

Orthographic projections are views of a 3D object, showing 3 faces of it. The 3 drawings are aligned so that if the page were folded, it would create part of the shape. It is also called Multiview projections. The 3 faces of an object consist of its plan view, front view and side view. There are 2 types of orthographic projection, which are first angle projection and third angle projection.

AFBC (atmospheric fluidized bed combustion) process consists of forming a bed of inert materials like finely sized ash or ash mixed with sand, limestone (for Sulphur removal), and solid fuel particles in a combustor and fluidizing it may forcing combustion air up through the bed mixture.

The gas flows through bed without disturbing particles significantly but gas velocity is high enough to support the total weight of bed (fluidization). At slightly higher velocity excess gas passes through the bed as bubbles (fluidized bed) and gives the bed the appearance of a boiling liquid

Bubbling fluidized bed combustion (BFBC) has a defined height of bed material and operates at or near atmospheric pressure in the furnace pressurized fluidized bed combustion (PFBC) system operates the bed at elevated pressure. Exhaust gases of sufficient energy to power a gas turbine, of course, gases need to clean.

In fluidized combustion, as ash is removed some unburned carbon is also removed resulting in lower efficiency. In circulating fluidized bed combustion system, bed is operated at higher pressure leading to high heat transfer, high consumption efficiency, and better fuel feed circulating

Fluidized beds operate with relatively high gas velocities and fine particle size the maintenance a steady state conditions in a past fluidized bed requires the continuous recycle of particles removed by the gas stream (circulating bed). The term circulating bed is often used to include fluidized bed systems containing multiple conventional bubbling beds between which bed material is exchanged

Thermal neutrons are slow neutrons (having energy below 1eV) which are in thermal equilibrium with their surroundings.

Pitching is a rocking action about a transverse axis through the vehicle, parallel to the ground. The front suspension moves out of phase with the rear, experiencing the rocking effect due to pitching.

Pipes are measured and sold with inner diameter. Pipes are used to transport fluids like water, oil, gas etc.

Tubes are measured and sold with outer diameter. Tubes are generally used for structural purposes.

Bearing is a device that helps smoother movement with minimal friction which in turn helps enhances efficiency and speed. Considering two types of loading, radial and thrust, there are different types of bearings which help handle these loads. The basic difference in the types of loads is essentially due to their ability to handle weight and different kinds of loads for various applications. Different types of bearings are:

• Ball bearing
• Ball Thrust bearing
• Roller thrust bearing
• Tapered roller bearing
• Roller bearing
• Giant Roller Bearing
• Magnetic bearing

The volume is a region that expands in cross sectional area as it wraps around the pump casing. The purpose of the Volute is to collect the liquid discharged from the periphery of the impeller at high velocity and gradually cause a reduction in fluid velocity by increasing the flow area.

This converts the velocity head to static pressure. The fluid is then discharged from centrifugal pump through the discharge connection.

The six-stroke engine is based on the concept of four stroke engine but built with an intention of improvising the efficiency in reducing emission. Every cycle of a four-cycle engine involves the upward and downward movement of the piston which happens twice in the chamber, resulting in four total strokes and one of which is the power stroke which provides the torque to move the vehicles.

A six-stroke engine works similarly except that there are two power strokes.

For ductile materials, theories of failure used are maximum shear stress theory, and maximum energy of distortion theory.

For the brittle materials, theory of maximum principal stress, maximum strain is used.

The following values are needed to be determined:

Thickness of the cylinder wall: The cylinder walls in an engine is made witness to gas pressure and the side thrust of a piston. This results in two types of stresses: longitudinal and circumferential stress. Both the types of stresses are perpendicular to each other and hence it is aimed to reduce the resulting stress as much as possible.

Length and bore of the cylinder: The length of the cylinder and the length of the stroke is calculated on the basis of the formula: length of cylinder L = 1.15 times the length of the stroke (l). L = 1.15(l)

Cylinder flange and studs: The cylinders are always cast integral as a part of the upper crankcase or in some cases attached to it by means of nuts and bolts. The flange is integral to a cylinder and henceforth its thickness should be greater than that of the cylinder wall. The thickness of flange should generally be between 1.2t-1.4t where it is the cylinder thickness.

The stud diameter is calculated by equating gas load (due to max pressure) to the grand total of all the resisting forces of the studs.

The common element between brass and bronze is copper.

A basic hole is one whose lower deviation is zero and in case of basic shaft the upper deviation is zero.

Independent suspension means it refers to the mounting of the wheel on a separate axis, so that road shocks affect only the particular wheel.

Large tyres provide larger surface area touching the ground, thus proving the more pulling power. Basically, tractors have larger rear tyres because tractors don’t have to operate at higher speeds, thus getting the same ground speed with larger tyres. More ever gear ratios don’t have to be as high as b/c of tyres.

The piston head is designed on the basis of the following considerations:

The crown should have enough strength to absorb the explosion pressure inside the engine cylinder.

The head must always dissipate the heat of the explosion as quickly as possible to the engine walls. The thickness of the head is calculated on the basis of another formula which takes into consideration the heat flowing through the head, the conductivity factor of the material. The temperature at the center and edges of the head.

The thickness of the piston head is calculated on the basis of the Grashoff`s formula which takes into consideration the maximum gas pressure of an explosion, the permissible bending and the outside diameter of the piston.

Generally, roller or hinged support are used to support the frames. The conditions of equilibrium are used to determine the reaction support of a frame. The condition of equilibrium takes place when the sum of the horizontal and vertical forces sum equal to zero. The system must form a state of equilibrium even after considering the external loads and the reactions at the supports. For equilibrium to be prevalent in the system the following conditions are required to be in occurrence:

• Summation of V = 0. This implies that the summation of all the forces in the vertical direction results to zero.
• Summation of H = 0. This implies that the total of all the forces acting in horizontal direction is also zero.
• Summation of M = 0. The sum of all the moment of forces around a point must be zero.

Pros:

• The high-octane rate enables it to blend better with air and to burn completely, generating less carbon. With less carbon buildup, spark plugs often last longer and oil changes are needed less frequently.
• Since it burns in the gaseous phase, it results in less corrosion and engine wear.
• In case of a spill, LPG evaporates quickly.

Cons:

• The LPG requires servicing at approximately once a year.
• Since complete combustion occurs, more heat is liberated which is not advised for a long journey as the engine will get over heated.
• Installation of LPG is rather difficult.

Octane Number: Octane number is defined as the percentage, by volume, of iso octane in the mixture of iso octane and h-heptane. It is the measure of rating of SI engine.

Cetane Number: Cetane number is defined as the percentage, by volume, of n-cetane in the mixture of n-cetane and alpha methylnaphthalene. It is the measure of rating of CIengine.

Riser as a checking process to confirm the molten metal has filled the cavity or not. Riser works as a backup reservoir of molten metal when the cavity metal volume shrinks due to solidification.

• Computer Aided Design (CAD) Software
• Mathcad
• Finite Element Analysis (FEA) Software
• Microsoft Excel
• MATLAB
• MechaniCalc
• Solidworks
• Analysis Software
• Computer-Aided Manufacturing (CAM)
• Computational Fluid Dynamics (CFD)
• Computer Aided Engineering (CAE)