# Mechanical Metallurgy Questions and Answers – Fatigue of Metals – Cumulative Fatigue Damage & Sequence Effects – 1

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This set of Mechanical Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Fatigue of Metals – Cumulative Fatigue Damage & Sequence Effects – 1”.

1. Find the crack growth per cycle for a steel plate where the crack growth equation is given by:
-> da/dN = A(ΔK)p
The value of p=3, A= 6.9*10-18, and stress intensity factor variation is 1 kPa m1/2.
a) 6.9 m/cycle
b) 6.9 mm/cycle
c) 6.9 nm/cycle
d) 13.3 m/cycle

Explanation: The crack growth is given as follows:
-> da/dN = A (ΔK)p
-> da/dN = 6.9*10-18 * (1*103)3
-> 6.9*10-9
da/dN = 6.9*10-9 m/cycle
So the crack growth per cycle is 6.9 nm.

2. The stress concentration factor and fatigue strength reduction factor are the same quantity.
a) True
b) False

Explanation: The Stress concentration factor is the ratio of maximum stress to the nominal stress of the component, whereas the fatigue strength reduction factor is ratio of fatigue strength of notched specimen to unnotched specimen.

3. The fatigue strength reduction factor is not affected by ____________
a) the severity of the notch
b) type of notch
d) critical resolved shear stress

Explanation: There is no direct link between the critical resolved shear stress and the fatigue strength reduction factor for a component.

4. Which of the following statement is correct?
a) Kf is generally less than Kt
b) Kf is usually more than Kt
c) There is no relation between the Kf and Kt of a material
d) The Kf and Kt has to be same of any material

Explanation: Generally it is observed that Kf is less than Kt for any material. Also, the ratio of Kf/Kt decreases as Kt increases.

5. A very sharp notch having high Kt has more effect on the fatigue strength than it would be expected from the value of Kt.
a) True
b) False

Explanation: A very sharp notch having high Kt have less effect on the fatigue strength than it would be expected from the value of Kt.

6. The relationship between the Kf and Kt is defined as ____________ (where q is notch sensitivity factor).
a) Kf=q+Kt
b) q=(Kf-1)/(Kt-1)
c) q=(Kf)/(Kt-1)
d) q=(Kf-1)/(Kt)

Explanation: The relationship between the Kf and Kt is defined as:
-> q=(Kf-1)/(Kt-1)

7. The material does not experience any reduction in the fatigue strength from the notch. The value of fatigue notch factor (Kf) for this material will be equal to ________
a) Kf=0
b) Kf=1
c) Kf=0.5
d) Kf=infinite

Explanation: The fatigue notch factor is the ratio of fatigue strength of the material with and without having a notch. So if both the strength is the same, the ratio will be equal to 1.

8. The material does not experience any reduction in the fatigue strength from the notch. The value of notch sensitivity factor (q) for this material will be equal to ___________
a) q=0
b) q=infinite
c) q=1
d) q=0.5

Explanation: The value of q is defined as:
-> q=->(Kf-1)/(Kt-1)
For the material with no reduction in fatigue strength form, the notch will have Kf equal to 1
Substituting the value in the equation:
-> q=(1-1)/(Kt-1)=0
So, the notch sensitivity factor will be equal to zero.

9. A material has notch sensitivity factor equal to one (q=1), the relation between the Kf and Kt for this material will be __________
a) Kf>Kt
b) Kf<Kt
c) Kf=Kt
d) no relation between them

Explanation: When q=1 and we know that:
-> q=(Kf-1)/(Kt-1)
-> 1=(Kf-1)/(Kt-1)
-> Kf=Kt.

10. The notch sensitivity factor ________ with an increase in the tensile strength of the material.
a) increases
b) decreases
c) remains the same
d) no relationship