JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III TESTING OF MATERIALS Previous Question Paper (February/March - 2022 - R18)

Hardness is defined as the resistance of a material to localized plastic deformation, such as indentation, scratching, or abrasion. It is a fundamental mechanical property that indicates a material's ability to withstand surface wear and penetration.

The importance of hardness testing lies in its ability to provide a quick, non-destructive assessment of material strength, wear resistance, and heat treatment effectiveness. It is widely used in quality control to verify material consistency and performance in applications involving friction or contact stress.

Common testing methods include:

• Brinell Hardness Test: Uses a hardened steel or tungsten carbide ball indenter under a specific load; the hardness value is calculated from the surface area of the indentation.
• Rockwell Hardness Test: Measures the depth of penetration under a major load compared to a minor load, providing a direct reading on the machine.
• Vickers Hardness Test: Utilizes a diamond pyramid indenter, suitable for a wide range of materials and thin specimens, measuring the diagonal lengths of the square impression.

Crack Opening Displacement (COD) is a fracture mechanics parameter that measures the distance between the two faces of a crack tip at the point of loading. It is used to quantify the toughness of materials that exhibit significant plastic deformation before failure, serving as a critical indicator of resistance to crack propagation.

The transition temperature curve represents the relationship between a material's impact energy (or ductility) and its operating temperature. Its significance includes:

• Ductile-to-Brittle Transition: It identifies the temperature range where a material shifts from ductile behavior (high energy absorption) to brittle behavior (low energy absorption).
• Safety Design: Engineers use this curve to ensure that the service temperature of a structure remains above the transition temperature to avoid catastrophic brittle fracture.
• Material Selection: It helps in selecting materials that maintain sufficient toughness under specific environmental conditions, particularly for low-temperature applications.