Structure And Properties Of Engineering Materials in Engineering Materials Science : Practice MCQ Questions & Answers with Explanations

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.

Explanation: Frenkel Defect (also known as the Frenkel pair/disorder) is a defect in the lattice crystal where an atom or ion occupies a normally vacant site other than its own. As a result, the atom or ion leaves its own lattice site vacant. Important Points Schottky Defect | Frenkel Defect

Explanation: Atomic packing factor: In the crystal structure, the atomic packing factor (APF) or packing efficiency or packing fraction is the fraction of volume in a crystal structure that is occupied by constituent particles. It is a dimensionless quantity and always less than unity. The atomic packing factor of different crystal structures is given in the table below: Unit Cell | Coordination No.

Explanation: The property of metals by which they can be beaten into thin sheets is known as malleability, e.g. copper, aluminium. The property of metals by which they can be drawn into thin wires is known as ductility, e.g.

Concept: In sheet metal work, different types of metal sheets are used. Galvanised iron sheets: Zinc coated iron is known as 'galvanized iron'. This soft iron sheet is popularly known as G.I sheets.

Y-alloy is a nickel-containing aluminium alloy that also contains copper and magnesium. It is lightweight, strong, and retains its strength at high temperatures, which makes it suitable for manufacturing pistons, cylinder heads, and other aircraft and automobile engine parts.

Concept: Ferromagnetic material: Ferromagnetic materials have a large, positive susceptibility to an external magnetic field. They exhibit a strong attraction to magnetic fields and can retain their magnetic properties after the external field has been removed. For example Iron, nickel, and cobalt.

When ferromagnetic material heated beyond curie temperature, turns into paramagnetic material, as the ferromagnetic domains become random. Curie temperature: Curie temperature is the temperature at which the magnetic properties of a material change. When the temperature is greater than the Curie temperature, ferromagnetic material becomes paramagnetic material.

Explanation: Ductility: Ductility is the property of a material that enables it to be drawn out or elongated to an appreciable extent before rupture occurs. It is the ability of a metal to exhibit large deformation or plastic response when being subjected to a tensile force. A tension test is done to check or measure ductility.

Concept: Thermosetting plastics: It is defined as a material which once shaped by heat and pressure is incapable of being re-processed by further applications of heat and pressure. This is because, during the shaping process, cross-links are introduced between the molecules which make up the basic resin or plastic. e.g.

Explanation: Effects of Various Elements in Steels Boron improves hardenability without the loss of (or even with some improvement in) machinability and formability. Calcium deoxidizes steels, improves toughness, and may improve formability and machinability. Carbon improves hardenability, strength, hardness, and wear resistance; it reduces ductility, weldability, and toughness.

Explanation: Unit Cell | Coordination No. | No. of Atoms Per Unit Cell | Atomic packing factor Diagram The unit cell of BCC crystal = 2 The unit cell of HCP crystal = 6 The difference between the number of atoms in a unit cell of HCP crystal and BCC crystal is 6 - 2 = 4

Concept: Stainless steels contain typically 10 - 30% chromium besides other elements like C, Mn, Si, S etc. Chromium imparts corrosion resistance to steel. Varying amounts of other alloying elements like Ni, Mo, V, Ti, Ni, etc.

Concept: Elasticity is the property of a material to regain its original shape after deformation when the external forces are removed. All materials are plastic to some extent but the degree varies, for example, both mild steel and rubber are elastic materials but steel is more elastic than rubber. Modulus of Elasticity or Young’s modulus is the slope of the stress-strain curve in the elastic region.

Explanation: Hexagonal closed pack structure: In a hexagonal closed-packed structure, the third layer has the same arrangement of spheres as the first layer. Since the structure repeats itself after every two layers, the stacking for hcp may be described as "a-b-a-b-a-b". The atoms in a hexagonal closed packed structure efficiently occupy 74% of space while 26% is empty space.

Concept: The correct match is, Resilience - Capacity of a material to absorb energy elastically Fatigue - Failure of material at loads less than that at normal conditions Stiffness - Resistance of the material to elastic deformation Elasticity - Ability of the material to return to the original shape when the load is removed Resilience It is the total strain energy stored in a given volume of material within the elastic limit. On removal of a load, this energy is released. In other words, it is the area under the load-deflection curve within the elastic limit.

Explanation: Engineering Ceramics: The properties of ceramic materials, like all materials, are dictated by the types of atoms present, the types of bonding between the atoms, and the way the atoms are packed together. The atoms in ceramic materials are held together by a chemical bond. The two most common chemical bonds for ceramic materials are covalent and ionic.

Explanation: Atomic Packing Factor: In the crystal structure, atomic packing factor (APF) or packing efficiency or packing fraction is the volume of atoms in a unit cell divided by the volume of the unit cell. It is a dimensionless quantity and always less than unity No of atoms in b.c.c unit cell = 2 For BCC $a = \frac{{4r}}{{\sqrt 3 }}$ where a is the side of the cube and r is the atomic radius. Now APF will be $APF = \frac{{{N{atoms}}{V{atom}}}}{{{V{crystal}}}} = \frac{{2\left( {\frac{4}{3}} \right)\pi {r^3}}}{{{{\left( {a } \right)}^3}}}= \frac{{2\left( {\frac{4}{3}} \right)\pi {r^3}}}{{{{\left( {\frac{{4r}}{{\sqrt 3 }}} \right)}^3}}}$ $APF = \frac {\sqrt {3} \pi}{8}$ Unit Cell | Coordination No.