GATE MT topic:fatigue PYQs & Answers — Page 2

Questions 11–20 of 25. Imported answers require independent review unless marked reviewed.

A specimen containing maximum initial surface crack of size 1.5 mm is subjected to cyclic loading with

and

. Assuming specimen geometric factor of 1, and referring to the given figure, the crack growth rate in

m cycle

is __________ (round off to nearest integer).

Diagram for Metallurgical Engineering question 64

Given: N = number of cycles a = crack length R = stress ratio

= stress intensity range

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While designing a material for high temperature application, which of the following characteristic(s)/attribute(s) is(are) desirable for achieving better creep resistance?

Your answerSelect all correct options. You can choose more than one.

Fine grain size

FCC crystal structure

High melting point

Cold worked microstructure

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Match the phenomena (Column I) with the descriptions (Column II)

Column I (P) Cottrell atmosphere (Q) Suzuki interaction (R) Bauschinger effect (S) Nabarro-Herring creep

Column II (1) Decrease in yield stress when loading direction is reversed (2) Stress assisted diffusion of vacancies resulting in plastic deformation in a polycrystalline material (3) Lüders bands (4) Segregation of solutes to the stacking fault

Your answerChoose one option.

P – 1, Q – 2, R – 3, S – 4

P – 1, Q – 2, R – 4, S – 3

P – 3, Q – 4, R – 1, S – 2

P – 3, Q – 1, R – 4, S – 2

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From high temperature tensile test, the flow stress (measured at the same value of strain) of an alloy was found to be 50 MPa at a strain rate of

and 70 MPa at a strain rate of

. The strain rate sensitivity parameter is ______ (round off to 3 decimal places).

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High cycle fatigue data for an alloy at various alternating stresses,

(see figure) is given below.

Stress, (MPa)	, Number of cycles to failure
500	1000
400	10000
300	100000
200	1000000

A specimen of this alloy is subjected to multiple stress cycles sequentially in the following order: (i) first 5000 cycles at

MPa followed by (ii) 25000 cycles at

MPa and finally (iii) at

MPa. Assuming that Miner’s law is obeyed, the number of cycles to failure at the final applied stress of 500 MPa is __________.

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Which one of the following is FALSE for creep deformation?

Your answerChoose one option.

The minimum creep rate is obtained in the primary stage (stage I).

Creep resistance decreases with decrease in grain size.

Coble creep occurs via grain boundary diffusion.

Nabarro-Herring creep occurs via lattice diffusion.

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Determine the correctness or otherwise of the following Assertion [a] and the Reason [r]

Assertion [a]: Low-alloy steels used for medium-temperature creep resistance often have additions of strong carbide-forming elements.

Reason [r]: During creep deformation, the particles with higher misfit with the matrix, lose coherency.

Your answerChoose one option.

Both [a] and [r] are true and [r] is the correct reason for [a].

Both [a] and [r] are true but [r] is not the correct reason for [a].

Both [a] and [r] are false.

[a] is true but [r] is false.

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The steady state creep rate of a material increases by a factor of 20 when the temperature is increased from 890 K to 980 K. The creep rate at a temperature of ______ K (round off to the nearest integer) will be 5 times the creep rate at 890 K.

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Crack growth is being continuously measured in a test specimen subjected to constant amplitude cyclic stress with a mean stress of zero. The crack growth rate is related to the stress intensity range, ΔK as

where, a is the crack length and N is the number of cycles. When the crack length increases by a factor of two, the crack growth rate will increase by a factor of ______ (round off to one decimal place).

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In a tensile creep test of a metal, Nabarro-Herring mechanism is favored over Coble mechanism for ____________.

Your answerChoose one option.

larger grain size and lower temperature

smaller grain size and higher temperature

larger grain size and higher temperature

smaller grain size and lower temperature

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GATE MT topic:fatigue PYQs

Question 64

Question 32

Question 41

Question 46

Question 52

Question 8

Question 37

Question 51

Question 52

Question 17