JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II MECHANICAL METALLURGY Previous Question Paper (April - 2018 - R16)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions.
Part A
What is the condition required for the dislocation concept to be valid?
Answer
The dislocation concept is valid only when the crystal lattice is considered as a continuous elastic medium, meaning the strain fields around the dislocation core are treated using continuum mechanics rather than discrete atomic interactions.
Write the expression for fraction of lattices that are vacant at a given temperature.
Answer
The fraction of vacant lattice sites (n/N) at a given temperature T is given by the expression:
where Qv is the energy required for vacancy formation, k is the Boltzmann constant, and T is the absolute temperature.
What are the limitations of Brinell hardness?
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Why knop hardness number increases as the load is decreases below 300gm.
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Define the terms toughness and resilience.
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The Izod test does not lend itself to testing specimen as a function of temperature. Why?
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Define stress concentration factor.
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Why are the notched fatigue properties of gray cast iron is almost equal to the un-notched properties?
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Define the term transient creep.
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How are large stress concentrations occur in third stage of creep?
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Part B
Explain in detail the Frank Reed sources.
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Determine the critical resolved shear stress for an iron crystal which deforms by simultaneous slip on (110)[-111], (110)[-11-1], (-110)[111] and (-110)[11-1] when the tensile stress along [010] is 95.2 MPa.
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Explain with neat sketch the point defects.
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If a material has a dislocation density of 1012 cm-2. What is the average distance between dislocations?
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Derive Griffith’s theory for brittle materials? And also write the modification of this theory.
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Write short notes on Shore and Poldi hardness methods.
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Explain with neat sketch the Rockwell hardness test.
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Estimate the theoretical fracture stress of iron, if the surface energy is 1.2 J/m2. How does this compared with the highest observed strength of heat-treated steels.
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Derive the relationship for the toughness of a metal when true stress-strain curve obeys the power law
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Explain with neat sketch the charpy test.
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Differentiate between tension test and compression test.
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Determine the fracture toughness of a material using COD test.
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Explain with neat sketch the different types of stress cycles.
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Draw the S-N curve for ferrous and non-ferrous metals? Explain its importance.
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Explain the effect of size on fatigue properties.
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Explain the effect of surface roughness on fatigue properties.
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Explain the different stages of creep curves.
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Explain the structural changes during creep.
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Explain the mechanism of Dislocation glide in creep.
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Explain the mechanism of Dislocation creep.
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