Mechanical Behaviour Questions and Answers – Mechanism of Fatigue

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

1. Which of the following is not a reason for crack initiation?
a) Inclusions
b) Gas pores
c) Local soft spots
d) Vacancy
View Answer

Answer: d
Explanation: Vacancy is not a direct reason for failure. Its size is of nano level. Inclusions, gas pores and soft spots can cause crack initiation.

2. Crack mostly starts at _________
a) Surface
b) Inclusion
c) Pore
d) Soft spots
View Answer

Answer: a
Explanation: Cracks mostly start at the surface. Because grains at the surface are more free than those in bulk.

3. Orowan’s theory is related to _________
a) Grain boundaries
b) Weak crystal
c) Slip band
d) Gas pores
View Answer

Answer: b
Explanation: Orowan considered favorably oriented surface grains to be the weak regions. These grains cause fatigue crack to initiate.

4. Wood’s theory is described by _________
a) Microscopic voids
b) Microscopic slip bands
c) Weak crystal
d) Grain boundaries
View Answer

Answer: b
Explanation: According to W.A. Wood, microscopic slip bands are formed on cyclic stress application. These are the source of fatigue cracks.

5. Slip band are notch root of _________ dimensions.
a) Micro
b) Macro
c) Nano
d) Atomic
View Answer

Answer: d
Explanation: These slip bands act as stress raisers. These are of atomic dimension. These are responsible for crack initiation.
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6. Which theory defines fatigue failure using microscopic slip bands?
a) Orowan’s theory
b) Wood’s theory
c) Cottrell’s theory
d) Dislocation theory
View Answer

Answer: b
Explanation: Under cycling loading conditions, a material deforms on the same directions. According to Wood’s theory, fine slip movements cause microscopic slip bends formation.

7. What term is used for initial crack formation during fatigue?
a) Cracking
b) Stage I fatigue
c) Stage II fatigue
d) Micro cracking
View Answer

Answer: b
Explanation: Initial crack formation during fatigue is known as stage I fatigue. In order to create a tiny fatigue crack large numbers of stress cycles are required.

8. Stage of crack growth is called _________
a) I stage
b) II stage
c) III stage
d) IV stage
View Answer

Answer: b
Explanation: In stage I Nano size crack gets developed. After this, crack grows in size. This stage is then referred to as stage II fatigue.

9. Material with a high surface to volume ratio have _________ fatigue life.
a) Very low fatigue life
b) Very high fatigue life
c) Lower fatigue life
d) Improved fatigue life
View Answer

Answer: d
Explanation: Material with a high surface to volume ratio favours low temperature rise. It leads to the improved fatigue life of the sample.

10. Which of the following materials is predominated by thermal failure?
b) Actual
c) Nylon
d) Polycarbonate
View Answer

Answer: c
Explanation: Nylon falls under third group materials. These tend to fail predominantly by thermal failure.

11. Which of the following material fails by both hysteric heating and crack propagation?
a) Nylon
b) Polyethylene
c) Propylene
View Answer

Answer: d
Explanation: Plastics as PMMA, acetal and polycarbonate have medium value of loss compliance. These fail by both hysteric heating and crack propagation.

12. Fatigue initiation only occurs in slip planes in FCC metals.
a) True
b) False
View Answer

Answer: b
Explanation: Fatigue initiation is different from static stress conditions. In FCC, it may also occur in {1 0 0} and {1 0 0} planes.

13. Paris-Erdogan relationship is applicable to some ceramics and plastics along with metals.
a) True
b) False
View Answer

Answer: a
Explanation: Paris-Erdogan relationship was originally developed for metals. But it also describes some polymers and ceramics.

Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.

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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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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