JNTU
JNTU B.Tech III TESTING OF MATERIALS Previous Question Paper (August - 2022 - R18)
Answer any five questions. All questions carry equal marks.
Main
Using a plot between temperature versus energy absorbed, describe the effects of temperature on notch toughness.
Answer
The relationship between temperature and energy absorbed is represented by the Ductile-to-Brittle Transition (DBT) curve. At high temperatures, materials exhibit high energy absorption, characterized by a ductile fracture with significant plastic deformation. As temperature decreases, the energy absorbed drops sharply within a specific range known as the transition temperature range. At low temperatures, the material undergoes brittle fracture, absorbing very little energy, characterized by cleavage and minimal plastic deformation. The plot typically shows an upper shelf (ductile), a transition region, and a lower shelf (brittle), illustrating that notch toughness is highly temperature-dependent for body-centered cubic (BCC) metals.
Summarize the significance of transition temperature curve.
Answer
The transition temperature curve is critical for engineering design because it defines the temperature range below which a material becomes susceptible to catastrophic brittle failure. Its significance lies in: 1) Material Selection: Ensuring the operating temperature of a structure remains above the transition range to avoid brittle fracture. 2) Safety Assessment: Predicting the reliability of components subjected to impact loads in cold environments. 3) Quality Control: Serving as a benchmark for heat treatment and alloying processes to lower the transition temperature, thereby improving low-temperature toughness.
Explain the principle of Crack Tip Opening Displacement (CTOD) test to determine the fracture toughness of a material.
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With neat sketch explain the method of loading in Charpy and Izod impact tests.
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Explain the principle of crack opening displacement (COD) method to measure fracture toughness of materials. Mention the advantages and disadvantages of this method.
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Define modulus of elasticity. Mention the physical meaning.
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What is resilience and toughness of material? Why it is important to measure these properties?
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Explain the deformation characteristics of material using true stress – true strain curve.
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Draw the typical stress – strain curve for cast iron and discuss the changes in mechanical behavior and properties of cast iron subjected to loads.
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Describe the effects of strain rate applied to a specimen on the flow stress and flow properties.
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Discuss the effects of stress concentration on fatigue.
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Explain the importance of mean – stress data’s.
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Explain the four stages in fatigue process when a metal is subjected to cyclic stress.
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Describe the effects of specimen size and surface roughness on fatigue propagation.
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Describe the importance of creep curve.
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Explain the structural changes during creep using a plot between creep rate versus total strain.
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Explain the working principle, instrumentations involved and applications of Radiography testing method.
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Discuss the operating principle, advantages and limitations of Ultrasonic test method.
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