Plastic Deformation and Yield Criteria - Mechanical Behaviour of Materials - Metallurgical Engineering Previous Year Questions

1

2007 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2007

With \(\epsilon\) = true plastic strain and \(n\) = strain-hardening coefficient, necking in a cylindrical tensile specimen of a work-hardening metal occurs when

A

\(\epsilon = n\)

B

\(\epsilon = 2n\)

C

\(\epsilon = n^{0.5}\)

D

\(\epsilon = n^2\)

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2

2007 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2007

A perfectly plastic metal piece, with 4 mm × 4 mm cross-section and 25 mm length, is stretched to 100 mm. What is the deformed cross-section?

A

1 mm × 1 mm

B

2 mm × 2 mm

C

3 mm × 3 mm

D

4 mm × 4 mm

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3

2007 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2007

A solder wire does NOT work-harden at room temperature, even upon bending back and forth several times. This is because

A

the dislocations become immobilized during the bending process

B

the grains grow preferentially in the direction of deformation

C

the recrystallization temperature is below room temperature

D

the grains have a preferred orientation

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4

2007 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2007

The tensile yield strength of a ductile metal is 100 MPa. If the material is subjected to tensile stresses of \(\sigma_2 = \sigma_3 = 50\) MPa along the second and third principal directions, the material yields when

A

\(\sigma_1 = 50\) MPa in compression or 150 MPa in tension

B

\(\sigma_1 = 50\) MPa in compression or 50 MPa in tension

C

\(\sigma_1 = 100\) MPa in tension

D

\(\sigma_1 = 0\)

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5

2007 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2007

If a tensile stress of 3 MPa is applied, slip will occur on which of the following slip systems?

A

(1̅11)[0̅1̅1]

B

(11̅1)[1̅01]

C

(1̅11)[1̅01̅]

D

(111)[1̅01]

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6

2008 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2008

The yield point phenomenon observed in annealed low carbon steels is due to the presence of

A

silicon

B

chromium

C

phosphorous

D

carbon

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7

2009 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2009

A 3.0 mm diameter single crystal is loaded to 400 N along [001] direction. The resolved shear stress on \((111)[\bar{1}01]\) slip system is

A

5.8 MPa

B

11.5 MPa

C

23.1 MPa

D

46.2 MPa

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8

2010 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2010

Number of slip systems in an ideal close packed hexagonal structure is

A

3

B

12

C

24

D

48

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9

2010 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2010

If the true stress-true strain curve of a ductile material is represented by the equation \(\sigma = 1100 \epsilon^{0.30}\), the ultimate tensile strength (engineering) will be

A

853 MPa

B

753 MPa

C

653 MPa

D

553 MPa

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10

2010 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2010

The tensile test of a sheet material exhibits 20% elongation in length and 10% decrease in width. The plastic strain ratio is

A

2.37

B

1.37

C

1.17

D

0.87

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11

2012 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2012

Flow stress after 50% reduction in area of the annealed rod on cold rolling is approximately

A

750 MPa

B

650 MPa

C

609 MPa

D

559 MPa

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12

2013 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2013

If σ and ε are true stress and true strain, respectively, the maximum true uniform strain that can be imparted to a material obeying \( \sigma = 1050 \epsilon^{0.25} \) is __________

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13

2014 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2014

A body starts yielding when it is subjected to a stress state with principal stresses of 250 MPa, 50 MPa and −50 MPa. What is the yield strength of the material, in MPa, if Tresca yield criterion is obeyed? ______

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14

2014 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2014

The flow curve of an annealed metal is expressed as \( \sigma = 200\epsilon^{0.25} \), where σ is in MPa. If a rod of this metal is subjected to a true strain of ε = 0.3 by extrusion, the ideal plastic work of deformation per unit volume (in MJ/m³) is ______

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15

2017 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2017

Primary mechanisms of accommodating plastic strain at low temperatures in crystalline metals are:

A

twinning and dislocation-slip

B

dislocation-climb and dislocation-slip

C

dislocation-slip and diffusion

D

viscous-flow and dislocation-slip

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16

2017 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2017

A single crystal of an FCC metal is subjected to a sufficiently large tensile stress along the [110] direction to activate some of the slip systems. Which one of the following slip systems will be activated:

A

a/2 [1̄10](111)

B

a/2 [011](1̄11)

C

a/2 [011](11̄1)

D

a/2 [110](1̄11)

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17

2018 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2018

The c/a ratio of Zn (hcp) is 1.856. Slip at room temperature occurs most easily on which of the following slip systems in Zn?
Note: In hcp metals, the ideal c/a ratio is 1.633.

A

\(\{11\bar{1}0\} \langle 11\bar{2}0 \rangle\)

B

\(\{11\bar{1}0\} \langle 0002 \rangle\)

C

\(\{0001\} \langle 11\bar{2}0 \rangle\)

D

\(\{10\bar{1}1\} \langle 11\bar{2}3 \rangle\)

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18

2018 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2018

Determine the correctness (or otherwise) of the following Assertion [A] and the Reason [R]
Assertion [A]: Refractory BCC metals like W and Mo are less ductile than FCC metals like Ni and Pt at room temperature
Reason [R]: BCC metals have fewer independent slip systems than FCC metals

A

Both [A] and [R] are true and [R] is the correct reason for [A]

B

Both [A] and [R] are true, but [R] is not the correct reason for [A]

C

Both [A] and [R] are false

D

[A] is true but [R] is false

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19

2018 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2018

A single crystal of aluminium is subjected to 10 MPa tensile stress along the [321] crystallographic direction. The resolved shear stress on the (11\(\bar{1}\)) [101] slip system is ______ (in MPa to two decimal places)

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20

2019 · Metallurgical Engineering · Mechanical Behaviour of Materials · Plastic Deformation and Yield Criteria

Metallurgical Engineering (MT) 2019

During low strain rate (≤ 0.1 per second) deformation of a metal at room temperature, the one that deforms by twinning mode is ____________.

A

Fe

B

Mg

C

Al

D

Ni

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