# Mechanical Metallurgy Questions and Answers – Surface Effect & Fatigue – 1

This set of Mechanical Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Surface Effect & Fatigue – 1”.

1. High cycle fatigue is described by the _______________
a) Coffin-Manson equation
b) Basquin’s equation
c) Morrow’s equation
d) Manson equation

Explanation: The high cycle fatigue is generally associated with low-stress cycles. So the Basquin’s equation describes this behavior correctly.

2. The Basquin’s equation is represented as ______________
a) σa/2=σ’f (2N)b
b) σa=σ’f (2N)b
c) σa=σ’f (N)b
d) σa/2=σ’f (N)b

Explanation: The Basquin’s equation describe the relationship of low cycle fatigue which states that:
-> σa= σ’f (2N)b
where σa is alternating stress amplitude
σ’f is fatigue strength coefficient
b is fatigue strength exponent.

3. Smaller the value of b (fatigue strength exponent) _____________ the fatigue life.
a) longer
b) shorter
c) no relationship
d) intermediate

Explanation: Smaller the value of b (fatigue strength exponent), longer will be the fatigue life because alternating stress amplitude will be lower.

4. The equation of fatigue valid for entire range of fatigue life is given as _____________
a) Δε/2=Δεe/2+Δεp/2
b) Δε/2=Δεe/2+Δεp
c) Δε/2=Δεe+Δεp/2
d) Δε=Δεe/2+Δεp/2

Explanation: The fatigue cycle of the component consists of the elastic part and the plastic part. So this equation takes care of both the elastic and plastic region of the component during fatigue failure.

5. The ductile material gives best result in the high strain amplitude or high cycle fatigue, while the strong material gives best result in high-stress low cycle fatigue.
a) True
b) False

Explanation: The ductile material can withstand high strain without failing, so it gives best performance in the high cycle fatigue. The strong material can resist the deformation without causing excessive deformation, so it performs well in high-stress low cycle fatigue.
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6. The fatigue failure is divided into ______ major parts.
a) four
b) three
c) two
d) one

Explanation: The fatigue crack of failure mainly consists of 4 parts:
(i) Crack initiation
(ii) Slip band crack growth
(iii) crack growth on the plane of high tensile stress
(iv) Ultimate ductile failure.

7. Generally, the fatigue crack initiation takes place in which stage of the life of the component?
a) In the last stage – around 90% of life
b) In the beginning of life – around 10%
c) In the middle – around 50%
d) Can occur in any stage

Explanation: The progression of the fatigue crack is a slow process, however the first crack can be observed as early as 10% of the component life only.

8. Which stage of the fatigue crack is most significant in the low cycle fatigue?
a) Crack initiation
b) Slip band crack growth
c) Crack growth on the plane of high tensile stress
d) Ultimate ductile failure

Explanation: The crack growth on the plane of high tensile stress or also called the stage-II of the crack growth is longest for the low cycle fatigue.

9. Which stage of the fatigue crack is most significant in the high cycle fatigue?
a) Crack initiation
b) Slip band crack growth
c) Crack growth on the plane of high tensile stress
d) Ultimate ductile failure

Explanation: The Slip band crack growth or also known as stage-I of the crack growth comprises of the largest segment in the high cycle fatigue.

10. There is no evidence of the fatigue crack growth on the nanoscale level, or crystallographic direction does not play any role in deciding the fatigue behavior of any material.
a) True
b) False

Explanation: The growth of the fatigue crack is preferred along with specific crystallographic directions if the crack growth is along the plane of easy slip. It is also observed that sometimes particular grain will crack in fatigue while some remains untouched.

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