JNTU
JNTU B.Tech III MECHANICAL METALLURGY Previous Question Paper (May/June - 2019 - R13)
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.
Part A
Define and draw the dislocations present in the metals.
Answer
A dislocation is a linear crystallographic defect or irregularity within a crystal lattice. The two primary types are edge dislocations, where an extra half-plane of atoms is inserted into the lattice, and screw dislocations, where the lattice is distorted by a shearing force that creates a spiral ramp of atomic planes around the dislocation line.
Explain the point defects in crystalline materials.
Answer
Point defects are localized irregularities in the atomic arrangement of a crystal lattice. Key types include: 1) Vacancies, which are empty lattice sites where an atom is missing; 2) Self-interstitials, where an atom of the same type occupies a non-lattice site; and 3) Impurity atoms, which can be substitutional (replacing a host atom) or interstitial (fitting into the spaces between host atoms).
Define Joffe effect.
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What is meant by scratch hardness? Explain.
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Define the term resilience?
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Explain the stress intensity factor.
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Define stress ratio and amplitude ratio in presenting fatigue data.
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Draw and explain the typical fatigue stress cycles.
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Define the term transient creep.
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“Creep is one important manifestation of anelastic behavior”. Comment on it?
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Part B
Derive and explain the concept of critical resolved shear stress.
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Determine the tensile stress that is applied along the [1 1 0] axis of a silver crystal to cause slip on the (1 1 1) [1 0 1] system. The critical resolved shear stress is 5 MPa.
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Explain with the help of neat sketch the process of cross slip.
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Draw and explain the Burgers circuits for a positive edge dislocations.
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Explain the effect of notch on fracture.
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Explain the features of a fracture curve.
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List the precautions to be taken while performing Rockwell hardness test.
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Explain the Shore and Poldi hardness measuring methods.
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Explain about true stress and true strain. Obtain a relationship between true strain and conventional linear strain.
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Explain the principle and working of compression testing machine.
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Explain the Mode-I type of fracture toughness testing.
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Explain the effect of specimen thickness on stress and mode of fracture in fracture toughness testing.
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Draw and explain the important feature present in S-N curve for mild steel and Aluminium alloy.
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Explain the methods for determining S-N curve when the mean stress is not equal to zero.
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Explain with the help of neat diagram about the cyclic hardening and cyclic softening.
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Explain how fatigue behavior changes by the following factors: i) Surface Roughness ii) Size of the specimen.
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Explain the power-law relation in creep.
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Draw the creep deformation maps and explain about dislocation glide.
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Draw a plot for creep rate Vs total strain and explain how structural changes takes place during creep.
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Define creep. Explain the importance of steady state creep.
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