JNTU
JNTU B.Tech III MECHANICAL WORKING Previous Question Paper (January/February - 2023 - R16)
Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
How plane-stress conditions are defined?
Answer
Plane-stress conditions are defined when the stress components acting on one of the principal planes are zero. Specifically, for a thin plate in the xy-plane, the stress components normal to the surface (σz) and the shear stresses on the surface (τxz, τyz) are assumed to be zero, leaving only σx, σy, and τxy as non-zero components.
How the state of stress at a point is described?
Answer
The state of stress at a point is described by the stress tensor, which consists of nine components acting on the faces of an infinitesimal cubic element. In a 3D coordinate system, these include three normal stresses (σx, σy, σz) and six shear stresses (τxy, τyx, τxz, τzx, τyz, τzy). Due to equilibrium requirements, the shear stresses are symmetric (e.g., τxy = τyx), reducing the independent components to six.
Explain the significance of true stress – strain parameters.
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What do you mean by transverse plastic strains?
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Distinguish between cold working and hot working.
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What is the influence of temperature in metal working?
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What is the significance of coefficient of friction?
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What is controlled rolling?
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What is patenting?
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What is limit of drawability?
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Part B
Explain the advantages and limitations of Tresca criterion over Von Mises yield criterion.
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Differentiate between elastic deformation and plastic deformation.
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Consider the elemental cube whose faces represent the principal planes and draw maximum shear stress plane for the cube. Justify the answer in detail.
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Write the mathematical expression for Von Mises yield criterion and explain in detail.
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Show that constancy of volume results in e1 + e2 + e3 = 0 and 1 + 2 + 3 = 0.
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Why the relationship for conventional strain valid only for small strains but the relationship for true strain is valid for all strains?
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Explain the octahedral shear stresses and strains.
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Explain invariants of stress and strain.
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Show that the equations for significant stress and strain reduce to the values for a tensile test.
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What would be the effect of section thickness ‘h’ on the forging load if the friction were reduced to zero?
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Explain the effect of strain rate and microstructure on metal forming processes.
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Show how a value of flow stress independent of friction can be obtained with the compression test using an extrapolation method.
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Derive the expressions for flow stress and strain in plane-strain compression test.
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Explain the reasons for designing rolling mills with complex clusters of rolls.
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Explain the basic requirements for a rolling lubricant.
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What is planetary mill? Explain its characteristic features, advantages and limitations.
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Explain how bars and shapes are produced.
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Differentiate between piercing and extrusion processes.
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An aluminium thin-walled tube (radius/thickness = 20) is closed at each end and pressurized to 1,000 psi to cause plastic deformation. Neglect the elastic strain and find the plastic strain in the circumferential direction of the tube. The plastic stress-strain curve is given by
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Differentiate between tube sinking and tube drawing.
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Explain the principle of wire drawing operation.
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Differentiate between wire, rod and tube.
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