JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III TESTING OF MATERIALS Previous Question Paper (August/September - 2021 - R18)
Answer any five questions. All questions carry equal marks.
Main
What is indentation hardness testing?
Answer
Indentation hardness testing is a method used to determine the resistance of a material to permanent plastic deformation caused by the penetration of an indenter under a specified load. The test involves pressing a harder material, typically made of steel, tungsten carbide, or diamond, into the surface of the test specimen. The resulting size or depth of the indentation is measured and correlated to the material's hardness value. This technique is widely used in engineering because it is non-destructive to the bulk of the component, relatively simple to perform, and provides a reliable indicator of the material's yield strength and wear resistance.
Explain the measurement of material hardness by Brinell hardness test.
Answer
The Brinell hardness test measures the resistance of a material by forcing a hardened steel or tungsten carbide ball of diameter D into the surface of the specimen under a predetermined load P for a specified duration.
- The load P is applied and maintained for a period of 10 to 30 seconds to ensure full plastic deformation.
- After the load is removed, the diameter of the circular indentation d is measured using a low-power microscope in two perpendicular directions, and the average value is calculated.
- The Brinell Hardness Number (BHN) is calculated using the formula:
Where P is the load in kgf, D is the diameter of the ball in mm, and d is the average diameter of the indentation in mm. The test is particularly suitable for materials with coarse grain structures or non-homogeneous surfaces, such as castings, as the large indenter averages out local variations in hardness.
Describe the determination of metal toughness at different temperatures using Notched bar impact test.
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What is Crack Opening Displacement (COD) test in fracture toughness?
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Explain the reasons for measuring the ductility of materials.
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Compare the characteristics features between true-stress – true-strain curve with its corresponding engineering stress-strain curve.
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Summarize the conditions for the development of necking in tensile test.
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Draw the typical Stress-Strain curve for steel and explain the analysis of mechanical properties of steel.
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Draw the typical S-N curves for ferrous and non-ferrous metals and explain the major conclusions from the curve.
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Explain the mechanism of different fatigue stress cycles with stress versus cycles plot.
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Mention the effects of stress concentration on fatigue.
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Describe the mechanism of deformation process and structural changes at high temperature during creep.
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Discuss the working principle, advantages and uses of Ultrasonic testing method.
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