JNTU Exam Papers
Mechanical Working of Metals 2nd Sem Apr/May 2008
Answer any FIVE Questions
All Questions carry equal marks
1. (a) Present Mohr’s circle in three dimensions and explain it in detail.
(b) The state of stress is given by ?x=25 p and ?y=5p plus shearing stress ?xy.
On a plane at 45o counter clockwise to the plane on which ?x acts the state of stress is 50 Mpa tension and 5 Mpa shear. Determine the values of ?x, ?y, ?xy. [7+9]
2. (a) Explain how the percent elongation and percentage reduction in cross sectional area of a material related to its ductility and brittleness.
(b) What is anisotropy in yielding? Explain VonMises yield criteria for anisotropic materials having orthotropic symmetry. [8+8]
3. (a) Explain why pure metals have low recrystallization temperatures as compared with impute metals and alloys.
(b) What are the effects of friction in metal forming processes? Explain.
(c) What do you mean by constant-volume relationship in metal working process.
Explain it in detail with the help of suitable mathematical expression.[6+6+4]
4. (a) Describe the grain flow characteristics of metals in forging.
(b) Discuss the advantages and limitations of forging process. [8+8]
5. (a) What is angle of bite? Explain its significance in rolling.
(b) What is coefficient of friction? Explain its significance in rolling. [8+8]
6. (a) Calculate the minimum gage possible in hot rolling low-carbon steel strip at 7000F on a 23?? mill with steel rolls (?0 = 35,000 psi, ? = 0.4, E = 20×106 psi). What is the minimum gage for cold rolling on the same mill when ??
0=60,000 psi, ? = 0.1, E = 30×106 psi.
(b) What is rolling torque? How it is measured? [10+6]
7. (a) In the hot extrusion process of 12?? diameter and 36?? long aluminium billet
at 6000F and ?0 = 12,000 psi, what is the breakthrough pressure required to extrude a 3?? diameter bar if ? = 0.1?
(b) Explain the typical arrangement of extrusion tooling. [8+8]
8. (a) Show that the strain rate of wire being pulled through a die can be expressed by ?? = (2 tan ?)/r(dx/dt). What is the maximum strain rate for a 0.04 inch diameter wire pulled at 2,000 ft/min through a 100 semi-angle die?
(b) Compare the force required to give a 30% reduction in a 0. 5?? diameter wire in a 100 semi-angle die with the force required to produce the same reduction in a tube blank of 0.5?? outside diameter, 0.4?? inside diameter using a cylindrical mandrel. Assume that ? = 0.08 for both cases. [8+8]