JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year MECHANICAL METALLURGY Previous Question Paper (May - 2018 - R13)
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
Distinguish between edge dislocation and screw dislocations.
Answer
An edge dislocation is formed by the insertion of an extra half-plane of atoms, where the dislocation line is perpendicular to the Burgers vector. A screw dislocation is formed by a shearing action that creates a spiral ramp of atoms, where the dislocation line is parallel to the Burgers vector.
Distinguish between resolved shear stress and critical resolved shear stress.
Answer
Resolved shear stress is the component of the applied tensile or compressive stress acting on a specific slip plane and in a specific slip direction. Critical resolved shear stress is the minimum value of resolved shear stress required to initiate plastic deformation (slip) in a single crystal.
Why the effect of stress raisers is more significant in brittle than ductile materials.
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Explain what do you mean by superficial hardness test.
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What is DBTT curve and give its importance.
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Why does a brittle material not have stable crack growth?
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What is mean stress?
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What is the effect of surface roughness on the property of fatigue?
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What is steady-state creep?
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How creep rest is differ from tensile test?
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Part B
What are the two kinds of twins which are of interest to the metallurgist. Explain them in detail.
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Bring out the differences between i) Slipping ii) Twinning with respect to (1) amount of movement of atoms (2) microscopic appearance and (3) lattice orientation.
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What is dislocation? How it is formed? Explain.
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Define Burger’s vector and illustrate it on the sketch of an edge dislocation.
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Explain the significance of dislocations in the plastic deformation metals.
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Write a short note on hardness methods at elevated temperature.
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Explain the basis for selection of loads in Brinell’s method.
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How does hardness differ from scratch test and indentation test?
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Explain share and poldi hardness method.
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Explain the 2 types of index tests used in microhardness testing.
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Why Brinell’s test is preferred for hardness measurement of cast alloys.
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Explain with neat diagram the charpy test.
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Explain how to determine the fracture toughness based on CTOD test?
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Conditions for necking
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Effect of strain rate on tensile properties.
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Yielding phenomenon.
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Describe the conditions that increases the susceptibility of a metal component to failure by fatigue. How metal fatigue resistance can be measured.
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Fatigue is affected by temperature, discuss, the effects of high and low temperature on it.
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Explain the mechanism of fatigue failure with neat diagram.
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Explain with neat sketch the types of stress cycles that occur in fatigue materials.
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Write short notes on fracture at elevated temperature.
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Draw the creep deformation maps and explain it.
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Draw the creep curve and explain each stage of curve.
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What is stress –rupture test?
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