← MES Jr. Grade
Past Questions — 2025
For a ductile material, toughness is the measure of:
A)
resistance to scratching
B)
ability to absorb energy up to fracture
C)
ability to absorb energy till elastic limit
D)
resistance to indentation
Toughness is a fundamental material property defined as the ability of a material to absorb energy and deform plastically before it eventually fractures. In a stress-strain curve, toughness is represented by the total area under the curve from the origin to the point of fracture.
Analysis of options:
- Option (a) 'resistance to scratching' and Option (d) 'resistance to indentation' both describe 'Hardness', not toughness.
- Option (c) 'ability to absorb energy till elastic limit' describes 'Resilience' (the capacity of a material to absorb energy when it is deformed elastically and then release that energy upon unloading).
- Option (b) correctly identifies toughness as the total energy absorption capacity up to the point of failure (fracture), which is especially critical for materials subjected to impact loading.
Plastic deformation is caused by:
A)
stored elastic energy
B)
dislocation motion
C)
low value of modulus
D)
complex elastic stress
Plastic deformation refers to the permanent, non-reversible deformation of a material that occurs when the applied stress exceeds the yield strength. In crystalline materials (like metals), this process occurs primarily through a mechanism called 'slip'. Slip is the process by which planes of atoms slide over one another. This sliding is not a simultaneous movement of an entire plane of atoms, but rather the movement of linear defects known as 'dislocations' through the crystal lattice. As dislocations move, they break and reform bonds, allowing the material to deform permanently without fracturing.
Why other options are incorrect:
- a. Stored elastic energy: This is associated with elastic deformation (temporary), where the material returns to its original shape once the load is removed.
- c. Low value of modulus: The modulus of elasticity (Young's modulus) describes the stiffness of a material in the elastic region; it does not cause plastic deformation.
- d. Complex elastic stress: Elastic stress, by definition, results in elastic (reversible) deformation, not plastic (permanent) deformation.
The crystal structure of austenite is:
A)
body centered cubic
B)
face centered cubic
C)
hexagonal closed packed
D)
body centered tetragonal
In the study of the Iron-Carbon equilibrium diagram, iron exists in different allotropic forms depending on the temperature.
1. **Austenite (γ-iron)**: This is the stable phase of iron between 912°C and 1394°C. It possesses a **Face Centered Cubic (FCC)** crystal structure. Because of the FCC arrangement, austenite has larger interstitial sites, allowing it to dissolve more carbon compared to ferrite.
2. **Ferrite (α-iron)**: This is the stable phase at room temperature (up to 912°C) and possesses a **Body Centered Cubic (BCC)** structure. This corresponds to option (a).
3. **Delta Ferrite (δ-iron)**: This is the stable phase at very high temperatures (above 1394°C) and also possesses a **Body Centered Cubic (BCC)** structure.
4. **Martensite**: When austenite is quenched rapidly, it transforms into a non-equilibrium phase called Martensite, which has a **Body Centered Tetragonal (BCT)** structure. This corresponds to option (d).
5. **Hexagonal Closed Packed (HCP)**: While some metals exhibit HCP structures, the standard phases of pure iron/steel (Austenite, Ferrite) do not. This corresponds to option (c).
Therefore, the crystal structure of austenite is specifically Face Centered Cubic (FCC).
Write the characteristics of a grinding wheel. Also, write the factors that affect the performance of the grinding wheel.
Which one of the following defects is ‘Schottky defect’?
A)
Vacancy defect
B)
Compositional defect
C)
Interstitial defect
D)
Surface defect
A Schottky defect is a type of point defect in ionic crystals that occurs when a stoichiometric number of cations and anions are missing from their regular lattice sites, creating vacancies. Because it involves the absence of atoms/ions from the lattice, it is classified as a 'Vacancy defect'.
Detailed analysis of options:
- (a) Vacancy defect: Correct. Schottky defects are characterized by missing pairs of ions (vacancies) to maintain electrical neutrality.
- (b) Compositional defect: Incorrect. These refer to defects where the chemical composition varies (like non-stoichiometric defects), whereas a Schottky defect maintains the stoichiometry of the crystal.
- (c) Interstitial defect: Incorrect. An interstitial defect occurs when an atom occupies a site that is not a normal lattice point. A Frenkel defect is an example of an interstitial-vacancy pair, but a Schottky defect specifically involves only vacancies.
- (d) Surface defect: Incorrect. Surface defects are 2D imperfections (like grain boundaries or external surfaces), whereas Schottky defects are 0D point defects.
The process of producing film or thin sheets by squeezing a thermoplastics material between the revolving cylinders is known as:
A)
Lamination
B)
Contact moulding
C)
Calendaring
D)
Pressure bag moulding
Step-by-step reasoning:
1. **Analysis of the Process**: The question describes a process where thermoplastic material is squeezed between revolving cylinders to produce thin sheets or films. This is the fundamental definition of 'Calendaring'.
2. **How Calendaring Works**: In a calender machine, a softened plastic material is passed through a series of heated rollers (cylinders). The gap between the rollers determines the thickness of the final sheet, and the pressure applied ensures a uniform, smooth finish.
3. **Evaluating Other Options**:
- **Lamination (a)**: This is the process of bonding two or more layers of material together to create a composite. While it may involve rollers, its primary purpose is bonding, not the initial formation of a sheet from bulk thermoplastic.
- **Contact Moulding (b)**: This is a simple compression moulding technique where a material is placed in a heated mold and pressed. It does not involve revolving cylinders.
- **Pressure Bag Moulding (d)**: This is a variation of compression moulding where a flexible bag is used to apply uniform pressure to a part. It does not involve revolving cylinders.
4. **Conclusion**: Based on the mechanical action (squeezing between revolving cylinders) and the output (films/thin sheets), Calendaring is the only correct process.
A spherical drop of molten metal of radius 5 mm was found to solidify in 12 s. In how much time will a similar drop of radius 10 mm would solidify?
If m is the number of constraints in a linear programming with two variables x and y and non negativity constraints x > 0, y> 0; the feasible region in the graphical solution will be surrounded by how many lines?
A)
m
B)
m + 1
C)
m + 2
D)
m + 4
In a Linear Programming Problem (LPP) with two variables (x and y), the feasible region is the set of all points that satisfy all the given constraints simultaneously.
1. The problem states there are 'm' constraints. Each of these constraints is typically represented by a linear inequality (e.g., ax + by ≤ c), which defines a half-plane bounded by a straight line. Therefore, there are 'm' potential boundary lines from these constraints.
2. Additionally, the problem specifies non-negativity constraints: x > 0 and y > 0.
- The constraint x > 0 is bounded by the line x = 0 (the y-axis).
- The constraint y > 0 is bounded by the line y = 0 (the x-axis).
3. To find the total number of lines that can surround or bound the feasible region, we sum the boundary lines from the general constraints and the non-negativity constraints:
Total lines = (m constraints) + (1 line for x=0) + (1 line for y=0) = m + 2.
Therefore, the feasible region is surrounded by a maximum of m + 2 lines.
The product layout should be used when there is:
A)
Low volume of production on individual items
B)
Adequate time and motion study is difficult to make
C)
Large volume of production on individual items
D)
All of above
In Industrial Engineering, a Product Layout (also known as a Line Layout or Flow-shop Layout) is designed based on the sequence of operations required to manufacture a specific product.
1. Why Option (c) is correct: Product layouts are characterized by a fixed sequence of machines and workstations. This setup is highly efficient for mass production where a large volume of the same item is produced. Because the volume is high, the high initial cost of specialized machinery and the rigid layout are justified by the low variable cost per unit and high throughput rate.
2. Why Option (a) is incorrect: Low volume production of individual items (or high variety) typically requires a Process Layout (Functional Layout), where machines of the same type are grouped together to allow for flexibility in routing different products.
3. Why Option (b) is incorrect: Product layouts actually require very precise time and motion studies to achieve 'line balancing.' If time and motion studies are difficult to perform, it is nearly impossible to balance the line, leading to bottlenecks and idle time, making a product layout unsuitable.
Therefore, the primary prerequisite for implementing a product layout is a high volume of production for a standardized product.
In melting furnaces, the primary function of a refractory lining is to:
A)
Increase heat transfer
B)
Protect furnace structure and contain molten metal
C)
Accelerate melting
D)
Prevent chemical reactions
In melting furnaces, refractories are materials (such as alumina, silica, or magnesia) that can withstand extremely high temperatures without melting or decomposing. Their primary functions are: 1) Thermal Insulation: They protect the outer structural shell of the furnace (usually made of steel) from the intense heat of the molten metal, preventing the shell from melting or warping. 2) Containment: They provide a chemically stable and physically robust vessel to hold the molten metal.
Why other options are incorrect:
- Option (a): Refractories are designed to be insulators; they actually decrease heat transfer to the outside environment to maintain high internal temperatures.
- Option (c): Refractories do not accelerate the melting process; the heating element or fuel source does. In fact, excessive lining thickness can slow down heating due to insulation.
- Option (d): While refractories are chosen for their chemical compatibility with the metal, their primary 'function' is structural protection and containment rather than acting as a catalyst or inhibitor for chemical reactions.
What is tempering? Why is it done? Describe in brief, the various types of tempering.
If the number of arrival in a queue follows the Poisson distribution, then the inter arrival time obeys which one of the following distributions?
A)
Poisson’s distribution
B)
Negative exponential law
C)
Normal distribution
D)
Binomial
In Queueing Theory and Stochastic Processes, there is a fundamental mathematical relationship between the Poisson distribution and the Exponential distribution.
1. **Poisson Distribution**: This describes the number of events (arrivals) occurring within a fixed interval of time. If arrivals occur independently and at a constant average rate (λ), the probability of 'k' arrivals in time 't' is given by the Poisson formula.
2. **Inter-arrival Time**: This is the time elapsed between two successive arrivals.
3. **The Relationship**: If the number of arrivals follows a Poisson distribution with rate λ, the time between these arrivals follows an Exponential distribution (also known as the Negative Exponential law). Mathematically, the probability that the inter-arrival time 'T' is greater than a value 't' is equivalent to the probability that zero arrivals occur in the interval [0, t].
Using the Poisson formula: P(X=0) = (e^(-λt) * (λt)^0) / 0! = e^(-λt).
The Cumulative Distribution Function (CDF) of the inter-arrival time is therefore F(t) = 1 - e^(-λt), which is the CDF of the Exponential distribution.
**Why other options are incorrect:**
- **a. Poisson's distribution**: This describes the *count* of events, not the *time* between them. Time is a continuous variable, whereas Poisson is a discrete distribution.
- **c. Normal distribution**: This is a symmetric bell-shaped curve used for sums of independent variables (Central Limit Theorem), not for the memoryless inter-arrival times of a Poisson process.
- **d. Binomial**: This describes the number of successes in a fixed number of independent Bernoulli trials, which is not applicable to continuous time intervals.
Discuss in detail the various mechanisms of tool wear, such as flank wear, crater wear, notch wear, and built-up edge.
Pearlite phase in an iron-carbide phase diagram is:
A)
eutectic phase
B)
hypoeutectic mixture
C)
eutectoid mixture
D)
hypereutectic phase
In the iron-carbon (Fe-Fe3C) phase diagram, Pearlite is formed during the slow cooling of austenite at the eutectoid composition (approximately 0.76% carbon) at a temperature of 727°C. The eutectoid reaction is a solid-state transformation where one solid phase (Austenite) transforms into two different solid phases (Ferrite and Cementite). Pearlite is not a single phase, but a lamellar (layered) mixture of these two phases.
Why other options are incorrect:
- (a) Eutectic phase: The eutectic reaction involves a liquid phase transforming into two solid phases (Ledeburite is the eutectic mixture in the Fe-C system).
- (b) Hypoeutectic mixture: This refers to alloys with carbon content lower than the eutectic point (but higher than the eutectoid point), involving a mixture of primary austenite and eutectic structures.
- (d) Hypereutectic phase: This refers to alloys with carbon content higher than the eutectic point, involving primary cementite and eutectic structures.
Stroke of ram of shaper is adjusted by:
A)
Changing the pinion
B)
Changing the position of the crank pin
C)
Changing the position of lead screw
D)
None of above
In a shaper machine, the reciprocating motion of the ram is typically driven by a crank and slotted link mechanism (a type of quick-return mechanism). The length of the stroke of the ram is directly proportional to the distance between the center of rotation of the crank and the crank pin. By moving the crank pin closer to the center of rotation, the throw of the crank decreases, thereby shortening the stroke of the ram. Conversely, moving the crank pin further from the center increases the stroke length.
Analysis of other options:
- Option (a): Changing the pinion would typically alter the speed of the machine or the feed rate, not the stroke length.
- Option (c): The lead screw is used for the automatic cross-feed of the table, not for controlling the longitudinal stroke of the ram.
- Option (d): Incorrect, as option (b) is the standard mechanical method for adjusting stroke length in shapers.
Use of more acetylene with less volume of oxygen in an oxyacetylene torch produces a ___________ flame.
A)
Neutral
B)
Oxidizing
C)
Carburizing
D)
None of these
In oxy-acetylene welding, the type of flame produced depends on the ratio of oxygen to acetylene. There are three primary types of flames:
1. **Neutral Flame**: Produced when equal volumes of oxygen and acetylene are used. It is used for most general welding purposes.
2. **Oxidizing Flame**: Produced when there is an excess of oxygen (more oxygen than acetylene). This flame is hotter and is typically used for welding brass or bronze.
3. **Carburizing Flame**: Produced when there is an excess of acetylene (more acetylene than oxygen). This flame contains unburnt carbon (acetylene), which creates a 'reducing' atmosphere. It is characterized by three distinct zones (inner cone, acetylene feather, and outer envelope) and is used for welding high-carbon steels, hard-facing, or aluminum.
Since the question specifies the use of 'more acetylene with less volume of oxygen', the resulting flame is a carburizing flame.
A wide strip is rolled to a final thickness of 6.35 mm with a reduction of 30% the roll radius is 50 cm and coefficient of friction is 0.2. The point of contact is:
A)
0.5 radians
B)
0.0738 radians
C)
0.0123 radians
D)
0.0235 radians
Option B is correct: 0.0738 radians.
Addition of vanadium in steel results in improvement of:
A)
heat treatability by quenching
B)
hardenability
C)
fatigue strength
D)
resistance to oxidation at elevated temperature
Vanadium is a strong carbide-forming element used in alloy steels. Its primary effect is to refine the grain size of the steel (grain refinement) and increase hardenability.
1. **Hardenability (Correct):** Vanadium forms stable carbides (VC) that inhibit grain growth during heating. Smaller grains and the presence of vanadium in solution shift the TTT (Time-Temperature-Transformation) curve to the right, meaning the steel can be quenched more slowly or in larger sections while still achieving a martensitic structure. This directly increases the 'hardenability' of the steel.
2. **Heat treatability by quenching (Incorrect):** While vanadium affects the process, 'hardenability' is the specific technical term for the depth and ease with which a material can be hardened by quenching.
3. **Fatigue strength (Incorrect):** While grain refinement can indirectly improve fatigue life, vanadium is not added primarily for this purpose; elements like nickel or specific surface treatments are more critical for fatigue strength.
4. **Resistance to oxidation (Incorrect):** Oxidation resistance at elevated temperatures is primarily provided by Chromium (Cr), Aluminum (Al), or Silicon (Si), which form protective oxide layers on the surface. Vanadium does not provide significant oxidation resistance.
In die casting, the term ‘flash’ refers to:
A)
Excess metal that leaks out along parting lines
B)
Sudden solidification of molten metal
C)
A polishing operation after casting
D)
Molten metal splash during pouring
In die casting, 'flash' is a common casting defect or byproduct. It occurs when the molten metal is injected into the die cavity under high pressure. If the two halves of the die (the parting line) are not clamped together with sufficient force or if there is a slight misalignment, the high-pressure metal forces its way through the tiny gap between the die halves. This results in a thin, flat layer of excess metal protruding from the finished part along the parting line, which must be trimmed off during post-processing.
Why other options are incorrect:
- Option b: Sudden solidification is simply the process of freezing/cooling and is not termed 'flash'.
- Option c: Polishing is a finishing operation (like buffing) used to improve surface quality, not a term for excess metal.
- Option d: Molten metal splash is typically referred to as 'splatter' or 'spraying', which occurs due to turbulence or improper pouring, not specifically along the parting lines of a die.
Which sequence correctly outlines the basic steps of powder metallurgy?
A)
Sintering -> Compaction -> Blending -> Finishing
B)
Blending -> Compaction -> Sintering -> Secondary operations
C)
Compaction -> Sintering -> Blending -> Finishing
D)
Blending -> Sintering -> Compaction -> Finishing
Powder Metallurgy (PM) is a metal-forming process that follows a specific logical sequence to transform metal powders into a solid part. The standard steps are:
1. **Blending/Mixing**: The first step involves mixing the primary metal powder with alloying elements and lubricants (to reduce friction during pressing) to ensure a homogeneous distribution of materials.
2. **Compaction**: The blended powder is pressed in a die at high pressure to create a 'green compact'. This gives the part its initial shape and provides enough structural integrity for handling.
3. **Sintering**: The green compact is heated in a controlled atmosphere furnace to a temperature below the melting point of the main constituent. This causes the particles to bond through atomic diffusion, significantly increasing the strength and density of the part.
4. **Secondary Operations (Finishing)**: Depending on the requirements, the sintered part may undergo further processes such as machining, plating, heat treatment, or infiltration to achieve final dimensions or properties.
Comparing this to the options:
- Option (a) is incorrect because sintering cannot happen before compaction.
- Option (c) is incorrect because blending must occur before the powder is compacted.
- Option (d) is incorrect because sintering must follow compaction, not precede it.
Which of the following is not considered a secondary process in powder metallurgy?
A)
Heat treatment
B)
Impregnation
C)
Infiltration
D)
Sintering
Powder Metallurgy (PM) is divided into primary and secondary processes.
1. Primary Processes: These are the essential steps required to create a basic PM part. They typically include:
- Powder Production (Atomization, Chemical, etc.)
- Blending/Mixing
- Compaction (Pressing)
- Sintering (Heating the compact below its melting point to bond particles).
2. Secondary Processes: These are optional post-processing steps used to improve the mechanical properties, dimensional accuracy, or functional characteristics of the sintered part. Examples include:
- Heat Treatment (to increase hardness or strength)
- Impregnation (filling pores with oil or polymers for lubrication/sealing)
- Infiltration (filling pores with a lower-melting-point metal to increase density/strength)
- Sizing/Coining (for dimensional precision)
- Plating/Coating
Since Sintering is a fundamental primary step without which the powder compact would not become a solid structural component, it is not a secondary process. Therefore, option (d) is the correct answer.
In the grinding wheel of A 60 G 7 B 23, B stands for:
A)
resinoid bond
B)
rubber bond
C)
shellac bond
D)
silicate bond
In the standard marking system for grinding wheels, the alphanumeric code represents specific characteristics of the wheel. For the given code 'A 60 G 7 B 23':
1. 'A' represents the Abrasive type (A = Aluminum Oxide).
2. '60' represents the Grain size (Medium).
3. 'G' represents the Grade (Medium/Soft).
4. '7' represents the Structure (Medium).
5. 'B' represents the Bond type. In the standard nomenclature:
- V = Vitrified bond
- R = Resinoid bond
- B = Silicate bond (or sometimes used for specific organic/silicate types depending on the standard, but in the context of these options, B corresponds to Silicate).
- E = Rubber bond
- S = Shellac bond
6. '23' represents the manufacturer's specific code or wheel number.
Therefore, 'B' stands for the silicate bond. Resinoid is typically 'R', Rubber is 'E', and Shellac is 'S'.
What is gating ratio? What are the different elements of it? Explain its importance in casting.
Derive the coordination number and the atomic packing fraction of an FCC unit cell.
What is Cast Iron? Write its important characteristics and uses.