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
View Answer

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

Answer: b
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
c) type loading
d) critical resolved shear stress
View Answer

Answer: d
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
View Answer

Answer: a
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
View Answer

Answer: b
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.
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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)
View Answer

Answer: b
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
View Answer

Answer: b
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
View Answer

Answer: a
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
View Answer

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

Answer: a
Explanation: The notch sensitivity factor increases with an increase in the tensile strength of the material. In other words, harder the material more will be severity of the notch of fatigue strength.

Sanfoundry Global Education & Learning Series – Mechanical Metallurgy.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn