Properties of Materials MCQ Quiz - Objective Question with Answer for Properties of Materials - Download Free PDF

Explanation:

Compressive Strength of Materials

• Compressive strength is the capacity of a material to withstand axially directed pushing forces. When the limit of compressive strength is reached, materials are crushed. It is measured by applying a force to the material until it fails and recording the amount of force per unit area.

Cast Iron:

• Cast iron is an alloy of iron that contains 2-4% carbon, along with varying amounts of silicon and manganese and traces of impurities such as sulfur and phosphorus. The high carbon content makes cast iron very brittle, but it also significantly enhances its compressive strength. Cast iron has a compressive strength in the range of 600 MPa (megapascals) to 700 MPa, making it suitable for applications where high compressive loads are present. This high compressive strength is why cast iron is widely used in the construction of columns, bases, and other load-bearing structures.

Additional InformationOption 1: Copper

Copper is a ductile metal with excellent electrical conductivity, thermal conductivity, and corrosion resistance. However, its compressive strength is significantly lower than that of cast iron. Copper has a compressive strength of approximately 210 MPa. While copper is used in various engineering applications, particularly in electrical components and plumbing, its compressive strength is not comparable to that of cast iron.

Option 2: Mild Steel

Mild steel, also known as low carbon steel, contains approximately 0.05-0.25% carbon. It is known for its ductility, weldability, and relatively low cost. Mild steel has a compressive strength of about 250 MPa to 400 MPa, which is higher than that of copper but still lower than that of cast iron. While mild steel is widely used in construction, automotive, and manufacturing industries due to its versatility, it does not match the compressive strength of cast iron.

Option 3: Rubber

Rubber is a highly elastic material commonly used in applications requiring flexibility and resilience. However, rubber has a very low compressive strength compared to metals and alloys. The compressive strength of rubber varies depending on its formulation but typically ranges from 10 MPa to 20 MPa. Rubber's primary applications include seals, gaskets, and flexible joints, where its low compressive strength is not a limiting factor.

Explanation:

Brittleness in Materials

Definition: Brittleness is a property of materials that causes them to break or shatter without significant deformation when subjected to stress. Brittle materials absorb very little energy before fracture, making them susceptible to sudden catastrophic failure.

Correct Option Analysis:

The correct option is:

Option 2: In tools that need to withstand heavy impact.

Brittleness would be most undesirable in tools that need to withstand heavy impact. Tools such as hammers, chisels, or any equipment used in construction and manufacturing processes are frequently subjected to heavy impacts and stresses. If these tools were made of brittle materials, they would be prone to breaking or shattering upon impact, posing a significant safety risk to users and potentially causing damage to workpieces. Therefore, materials with high toughness and the ability to absorb impact without fracturing are preferred for such applications.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: In materials used in high-speed applications.

In high-speed applications, materials are required to have high strength and durability, but brittleness is not necessarily the most undesirable property. Depending on the specific application, materials can be designed to accommodate stresses and strains at high speeds. For instance, in some high-speed machinery, components might not experience heavy impacts but rather continuous and uniform loads, where brittleness might not be as critical a concern as in tools subject to heavy impact.

Option 3: In structural beams under static load.

Structural beams under static load primarily need to have high strength and the ability to bear loads without excessive deformation. While brittleness can be undesirable, it is not the most critical factor in this context. Ductility and strength are more critical properties for structural beams to prevent sudden failure and to ensure the structure can support loads safely over time. The primary concern would be the beam's ability to withstand static loads without excessive deflection or failure, rather than the impact resistance.

Option 4: In materials exposed to high temperatures.

High temperatures can affect the mechanical properties of materials, but brittleness is not the sole concern. Materials exposed to high temperatures must maintain their strength, thermal stability, and resistance to thermal expansion. While brittleness at high temperatures can be problematic, it is typically addressed by selecting materials that resist thermal degradation and maintain ductility and toughness even at elevated temperatures.

Conclusion:

Understanding the importance of material properties such as brittleness in different applications is crucial for ensuring safety and functionality. In the context of tools that need to withstand heavy impact, brittleness is highly undesirable because it can lead to sudden and catastrophic failure, posing significant safety risks. In other applications, such as high-speed machinery, structural beams under static load, and materials exposed to high temperatures, brittleness can be managed or is less critical compared to other material properties like strength, ductility, and thermal stability.

Explanation:

Why does stainless steel resist rusting, while regular carbon steel does not?

Correct Option Analysis:

The correct option is:

Option 2: Stainless steel has a protective chromium oxide layer that prevents rusting.

Stainless steel is renowned for its resistance to rust and corrosion, a characteristic that significantly differentiates it from regular carbon steel. This resistance is primarily due to the presence of chromium in stainless steel, which forms a protective layer of chromium oxide on the surface. This layer acts as a barrier, preventing oxygen and moisture from reaching the underlying metal, thereby inhibiting the process of rust formation.

Detailed Solution:

Stainless steel is an alloy composed of iron and a minimum of 10.5% chromium, along with other elements such as nickel, molybdenum, and sometimes titanium. The key to its corrosion resistance lies in the chromium content, which reacts with oxygen in the environment to form a thin, stable layer of chromium oxide (Cr₂O₃) on the surface of the steel.

Formation of Chromium Oxide Layer:

When stainless steel is exposed to oxygen, either in the air or in water, the chromium present in the steel reacts with the oxygen to form chromium oxide. This layer is incredibly thin, usually just a few nanometers thick, but it is highly effective at protecting the steel. The chromium oxide layer adheres strongly to the surface and is impermeable to water and air, preventing these elements from penetrating and reaching the iron in the steel. As a result, the iron remains protected from oxidation, which is the chemical process that causes rust.

Self-Healing Property:

One of the remarkable features of the chromium oxide layer is its ability to self-heal. If the surface of the stainless steel is scratched or damaged, exposing the bare metal, the chromium in the steel will react with oxygen again to form new chromium oxide. This self-repairing capability ensures that the protective layer is quickly restored, maintaining the steel's resistance to rust over time.

Comparison with Regular Carbon Steel:

Regular carbon steel, on the other hand, lacks this protective chromium oxide layer. Carbon steel is primarily composed of iron and carbon, with very little to no chromium content. Without chromium, carbon steel cannot form a protective oxide layer. When carbon steel is exposed to moisture and oxygen, the iron reacts with these elements to form iron oxide (Fe₂O₃), commonly known as rust. Unlike chromium oxide, iron oxide is not adherent or protective; it flakes off and exposes more iron to further oxidation, leading to continuous rusting and degradation of the steel.

Additional Alloying Elements:

Besides chromium, stainless steel often contains other alloying elements that enhance its properties. Nickel is commonly added to improve ductility and toughness, while molybdenum increases resistance to pitting and crevice corrosion in chloride environments. Titanium can be added to stabilize the structure and prevent the formation of chromium carbides, which can deplete the chromium content and reduce corrosion resistance.

Applications of Stainless Steel:

Due to its corrosion resistance, stainless steel is used in a wide range of applications, including:

• Construction materials for buildings and infrastructure, especially in environments exposed to moisture.
• Medical instruments and surgical implants, where hygiene and durability are critical.
• Kitchenware and food processing equipment, where resistance to rust ensures safety and longevity.
• Automotive and aerospace components, which require materials that can withstand harsh conditions and maintain integrity over time.

Conclusion:

The corrosion resistance of stainless steel is a result of the formation of a protective chromium oxide layer, which prevents rust by blocking oxygen and moisture from reaching the iron in the steel. This feature, combined with the self-healing property of the chromium oxide layer, makes stainless steel an ideal material for applications requiring durability and resistance to environmental factors. In contrast, regular carbon steel lacks this protective layer and is prone to rust when exposed to moisture and air.

Additional Information:

To further understand the analysis, let’s evaluate the other options:

Option 1: Stainless steel has a thicker iron content.

This option is incorrect because the iron content in stainless steel is not necessarily thicker or higher. The key difference lies in the presence of chromium and other alloying elements that provide corrosion resistance, rather than the quantity of iron.

Option 3: Stainless steel has higher carbon content which makes it corrosion resistant.

This option is incorrect as well. Higher carbon content does not contribute to corrosion resistance; in fact, it can make steel more prone to rust. The corrosion resistance of stainless steel is due to its chromium content, not carbon.

Option 4: Stainless steel is coated with a special anti-rust chemical.

This option is also incorrect. The corrosion resistance of stainless steel is inherent due to the chromium oxide layer formed naturally on its surface. It is not a result of any external coating or chemical treatment.

Understanding the composition and properties of stainless steel versus regular carbon steel is crucial for selecting the appropriate material for various applications, ensuring longevity and performance in environments where corrosion resistance is paramount.

Explanation:

Which of the following factors generally increases the brittleness of a material?

Definition: Brittleness is a material property that indicates how easily a material can fracture or break without significant deformation. It is the opposite of ductility. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Common examples of brittle materials include glass and ceramics.

Correct Option Analysis:

The correct option is:

Option 2: Low temperature

This option correctly identifies a factor that generally increases the brittleness of a material. When the temperature of a material is lowered, its ability to deform plastically before breaking is reduced, and it becomes more prone to fracture. This is because low temperatures reduce the mobility of dislocations within the material's crystal structure, which hampers its ability to undergo plastic deformation. As a result, materials tend to exhibit more brittle behavior at low temperatures.

Additional Explanation:

When materials are subjected to low temperatures, the atoms in their crystal lattice vibrate less. This reduced atomic vibration leads to a decrease in the ability of the material to deform plastically. In metals, for example, the mobility of dislocations (defects in the crystal lattice that allow for plastic deformation) is significantly reduced at low temperatures. This reduction in dislocation mobility means that the material is less able to absorb energy through plastic deformation, making it more likely to fracture in a brittle manner.

This phenomenon is particularly important in materials like steel, which can transition from ductile to brittle behavior at a critical temperature known as the ductile-to-brittle transition temperature (DBTT). Below the DBTT, steel becomes much more brittle and is more likely to fail catastrophically when subjected to stress.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: High alloy content

High alloy content can affect the mechanical properties of a material in various ways, depending on the specific alloying elements involved. While certain alloying elements can increase the hardness and strength of a material, they do not necessarily increase its brittleness. In some cases, alloying elements can actually improve the toughness and ductility of a material. Therefore, high alloy content is not a general factor that increases brittleness.

Option 3: High temperature

High temperatures generally increase the ductility of materials rather than their brittleness. At elevated temperatures, the atoms in a material have higher kinetic energy, leading to increased atomic vibrations and greater mobility of dislocations. This enhanced dislocation mobility allows the material to deform plastically more easily, making it less prone to brittle fracture. Therefore, high temperature is not a factor that increases brittleness.

Option 4: High strain rate

High strain rate can increase the brittleness of a material, but this effect is more complex and depends on the material and the specific conditions. When a material is subjected to a high strain rate, it has less time to undergo plastic deformation, which can lead to more brittle behavior. However, this effect is not as general or significant as the impact of low temperature on brittleness. Therefore, while high strain rate can contribute to brittleness, it is not the primary factor.

Conclusion:

Understanding the factors that influence the brittleness of a material is crucial for selecting the appropriate materials for various applications, particularly in environments where low temperatures are encountered. Low temperature is a primary factor that generally increases the brittleness of materials, as it reduces their ability to undergo plastic deformation. This knowledge is essential for designing materials and structures that must operate reliably under a wide range of temperatures.

Explanation:

Brittle Fracture

• Brittle fracture is a type of catastrophic failure that occurs in materials when they break suddenly without significant plastic deformation. It is characterized by a rapid propagation of cracks through the material, often along specific planes or grain boundaries. This type of failure is most common in materials with high tensile strength but low ductility.

Mechanism of Brittle Fracture:

• Brittle fracture typically occurs under tensile stress and is initiated by the formation of cracks at stress concentrations such as defects, voids, or sharp corners in the material. Unlike ductile fracture, which involves substantial plastic deformation, brittle fracture propagates rapidly, often at the speed of sound within the material. The fracture surfaces in brittle failure often exhibit a granular or crystalline appearance, which is indicative of its sudden and brittle nature.

Factors Leading to Brittle Fracture:

• Low Ductility: Materials that lack ductility (such as ceramics, glass, and certain high-strength steels) are more prone to brittle fracture.
• High Tensile Strength: While high tensile strength materials can withstand significant loads, their inability to deform plastically makes them susceptible to crack propagation under stress.
• Low Operating Temperature: Brittle fracture is more likely to occur at low temperatures where materials tend to lose ductility and become more brittle.
• Stress Concentration: Sharp notches, holes, or other geometric irregularities can act as stress concentrators, making the material more vulnerable to brittle failure.
• High Strain Rate: Rapid loading or impact can lead to brittle fracture, as the material does not have sufficient time to deform plastically.

Concept:

• The hardness of the mineral is defined on Moh's scale of hardness. On this scale, a mineral is rated between 1-10 on the basis of its strength.
• It is used to rate the hardness of a variety of substances and elements, not only metals. The softest materials it rates are assigned a rating of 1; the hardest earn a rating of 10.​ 

Explanation:

The Moh's scale of different minerals shown below -

• Tungsten is the hardest metal. ∴ Option 4 is correct.
• Platinum is a less hard metal. That's why it is used in Jewellery. It can make intricate designs. It is highly ductile.
• The name Tungsten originates from the Swedish name tungsten meaning heavy stone.
• Hardness is the ability to scratch making a dent on the surface of the metal. It is just a number measured using (Rockwell, Brinell, Vickers test)  Of which Brinell is most accurate.
• Gold: 25 Mpa
• Platinum: 40 Mpa
• Tungsten: 310 Mpa
• Iron: 150  Mpa
• Diamond: 10000 Mpa (Non-metal)
• It is a chemical element with atomic number 74 that has the highest tensile strength of all the metals present in the world. Its symbol is  "W"
• When combined with carbon, tungsten becomes stronger and even more durable. Tungsten carbide is the end product of mixing tungsten with carbon. Tungsten carbide is 4 times stronger than platinum with a hardness rating of 9 on the Mohs scale, softer only than diamond.
• From the above, 310 > 40, So, Tungsten is harder than Platinum.

Additional Information

• The Youngs Modulus value of Tungsten is 34.48 × 1010 Pa and 
• The Youngs Modulus value of Platinum is 14.48 × 1010 Pa 

Explanation:

• An alloy is a homogeneous mixture of two or more metals or nonmetals.
• Alloys are metal mixtures with other elements and the combination of both is governed by the properties required.
• The following table shows some metals with there alloys.

Important Points

Duralumin: It is an aluminium alloy. It contains 3.5 to 4.5% copper, 0.4 to 0.7% manganese, 0.4 to 0.7% magnesium and the remaining being aluminium. It is widely used in the aircraft industry for forging, stamping, bars, sheets, rivets, and so on.

Hindalium: It contains 5% copper and the rest aluminium. It is used for containers, utensils, tubes, rivets, etc.

Ductility

• Ductility is the property of the material that enables it to be drawn out or elongated to an appreciable extent before rupture occurs.
• The percentage elongation or percentage reduction in the area before rupture of a test specimen is the measure of ductility. Normally if the percentage elongation exceeds 15% the material is ductile and if it is less than 5% the material is brittle.
• Lead, copper, aluminium, mild steel are typical ductile materials.

Brittleness

• Brittleness is the opposite of ductility. Brittle materials show little deformation before fracture and failure occur suddenly without any warning i.e. it is the property of breaking without much permanent distortion. Normally if the elongation is less than 5% the material is brittle. E.g. cast iron, glass, ceramics are typical brittle materials.

Malleability

• Malleability is the property by virtue of which a material may be hammered or rolled into thin sheets without rupture. This property generally increases with the increase of temperature.
• Malleability is the ability of a metal to exhibit large deformation or plastic response when being subjected to compressive force.
• Lead, soft steel, wrought iron, copper and aluminium are some materials in order of diminishing malleability.
• A material that can be beaten into thin plates is said to possess the property of malleability.

Elasticity: 

• When an external force acts on the body, the body tends to undergo some deformation.
• If the external force is removed, then the body comes back to its original shape and size, the body is known as elastic body and this property is called elasticity.

Plasticity: 

• A plastic material does not regain its original shape after removal of load. An elastic material regains its original shape after removal of load.

Ductility: 

• A property by virtue of which the substance can be drawn into a wire, is called ductile substance.

Explanation:

Elasticity is the ability of a body that resists body to distort under any force and try to return to its original shape and size when that force is removed.

Elasticity is measured from the modulus of elasticity which is defined as the ratio of stress to strain up to the elastic limit.

The modulus of elasticity or Young’s modulus is the slope of the stress-strain curve in the elastic region.

\(E = \frac{\sigma }{\epsilon}\)

The modulus of elasticity is highest for steel among the given materials and is taken as 200 GPa.

Explanation:

Steel is an alloy of iron and carbon, along with small amounts of other alloying elements or residual elements as well. The plain iron-carbon alloys (Steel) contain 0.002 - 2.1% by weight carbon. For most of the materials, it varies from 0.1-1.5%.

There are 3 types of plain carbon steel:

(i) Low-carbon steels: Carbon content in the range of < 0.3%

(ii) Medium carbon steels: Carbon content in the range of 0.3 – 0.6%.

(iii) High-carbon steels: Carbon content in the range of 0.6 – 1.4%.

Resistance to corrosion: Is the ability of a material that resists against reaction with caustic elements that corrode or degrade the material.

Ultimate Strength: The maximum strength the material can withstand without breaking.

Hardness is defined as the resistance of a material to penetration or permanent deformation. It usually indicates resistance to abrasion, scratching, cutting or shaping.

Ductility is the ability of a material to withstand tensile force when it is applied upon it as it undergoes plastic deformation, this is often characterized by the material's ability to be stretched into a wire. 

With the increase in carbon content, the strength, hardness, and brittleness increase but the ductility and toughness decrease.

Because with an increase in carbon the cementite phase in the material increases and since cementite is hard and brittle so the ductility decreases with an increase in carbon.

Soft magnetic materials have a small area of the hysteresis loop.

Hysteresis Loop (B.H Curve):

• Consider a completely demagnetized ferromagnetic material (i.e. B = H = 0)
• It will be subjected to the increasing value of magnetic field strength (H) and the corresponding flux density (B) measured the result is shown in the below figure by the curve O-a-b.
• At point b, if the field intensity (H) is increased further the flux density (B’) will not increase anymore, this is called saturation b-y is called solution flux density.
• Now if field intensity (H) is decreased, the flux density (B) will follow the curve b-c. When field intensity (H) is reduced to zero, flux remains the iron this is called remanent flux density or remanence, it is shown in fig. O-C.
• Now if the H increased in the opposite direction the flux density decreases until the point d here the flux density (B) is zero.
• The magnetic field strength (points between O and d) require to remove the residual magnetism i.e. reduce B to zero called a coercive force.
• Now if H is increased further in the reverse direction causes the flux density to increase in the reverse direction all the saturation point e.
• If H is varied backwords OX to O-Y, the flux Density (B) follows the curve b-c-d-d.
• From the figure the clear that flux density changes ‘log behind the changes in the magnetic field strength this effect is called hysteresis.
• The closed figure b-c-d-e-f-g-b is called the hysteresis loop.

• The energy loss associated with hysteresis is proportional to the area of the hysteresis loop.
• The area of the hysteresis loop varies with the type of material.
• For hard material: hysteresis loop area large → hysteresis loss also more → high remanence (O-C) and large coercivity (O-d).
• For soft material: hysteresis loop area small → hysteresis loss less → large remanence and small coercivity.

Note:

The difference between soft magnetic materials & hard magnetic materials is as shown:

The schematic arrangements of spins of four different types of magnetic materials are as follows:

Explanation:

Co-efficient of expansion:

• The coefficient of expansion of a material is numerically equal to the ratio of increase in length, area or volume to its original length, area or volume when the material is heated by 1 °C.

Unit - °C^-1 or K^-1

Important Points

• Invar – It is an alloy of Nickel (36%) and Iron (64%).

Explanation:

Tungsten: 

• The metal tungsten is used for the filaments in incandescent bulbs.
• It has a high melting point and retains its strength when heated.
• Filaments of the light bulbs are made up of the Tungsten element.
• Its symbol is ‘W’ because of its scientific name ‘Wolfram’ and its and the atomic number 74. 
• As the resistance is less, heat energy is produced is very low which is not sufficient for an electric bulb to glow so the resistance is kept high.
• Tungsten is very resistant to corrosion and has the highest melting point (melting point = 3380 K) and the highest tensile strength of any element. Therefore option 3 is correct.
• Tungsten is used for making bulb filaments of incandescent lamps because it has the highest melting point and does not melt even while it is glowing for long hours. 
• Light bulb filaments aren't resistive because of the tungsten.
• They're resistive because of their very long length, and very thin wire.​

Explanation:

Stress-strain diagram:

It is a tool for understanding material behavior under load. It helps in selecting the right materials for specific loading conditions.

Various points are mentioned in the stress-strain diagram, the details are mentioned below:

Proportion limit (Hooke's Law):

• From the origin up to point 'P' called the Proportional limit, the stress-strain curve is a straight line i.e σ ∝ ε.
• If the stress is increased beyond the point P, the graph no longer remains a straight line and Hooke’s law is not obeyed.

Elastic limit:

• Point 'E' represents the elastic limit, the limit up to which the material will return its original shape and size when the load is removed.
• After point E, a small increase in stress, the strain increases faster and a graph bends towards the strain axis, and then if the load is removed, the material is unable to cover its original size and shape.

Yield point (Y_p):

• It is the point at which the material will have an appreciable elongation OR a slight increase in stress above the elastic limit that results in permanent deformation. This behaviour is called yielding for ductile materials. It is denoted by Y_p.
• Materials which is less ductile do not have a well-defined yield point, which is determined by the offset method- by which a line is drawn parallel to linear portion of the curve and intersecting at some values most commonly 0.2 %. It is denoted by point S.

Breaking stress / Ultimate stress:

• The maximum ordinate (stress) in the stress-strain diagram which represents the maximum load that a material can sustain without failure. It is denoted by point N.
• Necking: After the ultimate stress, the cross-sectional area begins to decrease in a region of the specimen which causes the apparent stress to rapidly decrease. This phenomenon is known as necking.

Breaking point:

Once the neck is formed, the material begins to thin out locally, where the strain increases faster even though stress is decreased and the material finally breaks at point B which is called breaking point.