Jawaharlal Nehru Technological University Hyderabad B.Tech III BASIC MECHANICAL ENGINEERING FOR CIVIL ENGINEERS Previous Question Paper (March - 2021 - R18)

An alloy is a metallic substance composed of two or more chemical elements, where at least one is a metal, combined through melting and solidifying to form a homogeneous solid solution or intermetallic compound. Alloys are typically isotropic, meaning their properties are uniform in all directions, and they are primarily used to enhance mechanical properties like strength, hardness, and corrosion resistance compared to pure metals.

A composite is a material formed by combining two or more distinct constituent materials—typically a reinforcing phase (fibers or particles) and a matrix phase—that remain separate and distinct at the macroscopic level. Composites are anisotropic, meaning their properties depend on the direction of loading and the orientation of the reinforcement. They are designed to achieve specific combinations of properties, such as high strength-to-weight ratios, that cannot be obtained by either constituent alone.

Heat treatment is the controlled process of heating and cooling metals to alter their physical and mechanical properties without changing their shape. The primary need for heat treatment is to modify internal microstructures to improve ductility, increase hardness, relieve internal stresses induced during manufacturing, or enhance wear and corrosion resistance.

Key applications include:

• Annealing: Used to soften metals to improve machinability and remove internal stresses.
• Normalizing: Applied to refine grain structure and produce a uniform, predictable mechanical property profile in steel components.
• Hardening (Quenching): Essential for tools, gears, and shafts that require high surface hardness and resistance to wear.
• Tempering: Performed after hardening to reduce brittleness and improve toughness in structural components.
• Case Hardening: Used for parts like cams and crankshafts that require a hard, wear-resistant surface while maintaining a ductile, shock-resistant core.