JNTU Previous Papers Mechanical Working of Metals IInd Sem Apr/May 2008

JNTU Previous Papers

Mechanical Working of Metals IInd Sem Apr/May 2008

Time: 3 hours Max Marks: 80

Answer any FIVE Questions

All Questions carry equal marks

SET-IV

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) Mention the various factors that affect the plastic deformation of metals. Give examples.

(b) Derive the expression

True stress=Engineering stress(1+ Engineering strain). [8+8]

 

3. (a) Explain the concept of work hardening. Is strain hardening and work hardening are the same? Or, is there any difference? If so explain. In what way ‘Work hardening’ will be helpful for metal deformation. Discuss fully.

(b) What is spring back? How can spring back effect offset? Explain the various factors that influence spring back. [10+6]

 

4. (a) What are the main characteristics of hot forging as compared with cold forging?

(b) Describe the following forging operations with the help of neat sketches and list out their applications.

i. Drawing out

ii. Setting down and furnishing. [8+8]

 

5. (a) What do you mean by profile rolling? Explain.

(b) How is the roll gap maintained in a rolling mill stand? What is its significance? [6+10]

 

6. With the help of simplified theory of rolling, plot curves for the variation of rolling load with roll diameter, coefficient of friction, and mean strip thickness. [16]

 

7. (a) Differentiate between piercing and extrusion processes?

(b) 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 ?= 25(?)0.25, where stress is in ksi. [6+10]

 

8. (a) 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 0.4?? outside diameter, 0.3?? inside diameter using a cylindrical mandrel. Assume that ? = 0.07 for both cases.

(b) Plot a curve of the ratio of draw stress to flow stress versus semi-angle die for the conditions ? = 0.06, r = 0.4 and Da = 0.2 in. [10+6]

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