# Mechanical Behaviour Questions and Answers – Low Cycle Fatigue

This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Low Cycle Fatigue”.

1. By decreasing the number of cycles, the allowable stress ________
a) Increases
b) Decreases
c) Remains constant
d) First Increases then decreases
View Answer

Answer: a
Explanation: Lower the number of cycles, the higher will be allowable stress. It can be explained by S-N curve.

2. What term is used for fatigue that occurs with less than 104 or 105 cycles?
a) High cycle fatigue
b) Low cycle fatigue
c) Fatigue limit
d) Stage II fatigue
View Answer

Answer: b
Explanation: The fatigue that occurs with less than about 104 or 105 cycles, is known as low cycle fatigue. It occurs when local maximum tensile stress around the crack tip is above the yield stress.

3. What is the limit for low cycle fatigue?
a) 100 cycles
b) 103 cycles
c) 104 cycles
d) 1010 cycles
View Answer

Answer: c
Explanation: Fatigue which occurs below 104 or 105 cycles is low cycle fatigue. Thermal conditions are considered here.
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4. Low cycle fatigue conditions are frequently created where the cyclic stresses are of ________ origin.
a) Kinetic
b) Impact
c) Thermal
d) Compressive
View Answer

Answer: c
Explanation: Low cycle fatigue occurs below 104 cycles. These conditions are frequently created by thermal origin. It is an important consideration in high-temperature systems.

5. For what purpose low cycle fatigue is an important consideration?
a) Subzero systems
b) High temperature systems
c) High load systems
d) Wet systems
View Answer

Answer: b
Explanation: Low cycle fatigue is created by stresses of thermal origin. It is an important consideration in high-temperature systems.
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6. Which law can predict the fatigue life in low cycle fatigue conditions?
a) Paris-Erodogan
b) Wood’s law
c) Orowan’s law
d) Coffin-Manson law
View Answer

Answer: d
Explanation: Coffin-Manson law can predict the fatigue life in low cycle fatigue conditions. A log-log plot between plastic strain ranges against the cycles is taken.

7. A log-log plot between the plastic strain range against the number of fatigue cycles yields ____________
a) Straight line
b) Parabola
c) Elliptical
d) Exponential
View Answer

Answer: a
Explanation: A log-log plot between the plastic strain ranges against the number of fatigue cycles yields a straight line. It can be shown by Coffin-Manson law.
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8. A smaller value of x results in _________ value of fatigue life.
a) Smaller
b) Larger
c) Constant
d) Zero
View Answer

Answer: b
Explanation: A smaller value of x results in a larger value of fatigue life. x is fatigue ductility exponent.

9. The fatigue ductility exponent x is always positive.
a) True
b) False
View Answer

Answer: b
Explanation: x is fatigue ductility exponent. It varies between -0.5 and -0.7. Its smaller value gives a large fatigue life.
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10. The fatigue ductility exponent x is always positive.
a) True
b) False
View Answer

Answer: b
Explanation: LCF is an important consideration in systems which undergo thermal transient. These include the components of the power plant.

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To practice all areas of Mechanical Behaviour & Testing of Materials, here is complete set of 1000+ Multiple Choice Questions and Answers.

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