# Mechanical Metallurgy Questions and Answers – Fatigue of Metals – S-N Curve – 2

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This set of Mechanical Metallurgy Questions and Answers for Campus interviews focuses on “Fatigue of Metals – S-N Curve – 2”.

1. The basic fatigue data is plotted in the form of ___________
a) Pourbaix diagram
b) Ellingham diagram
c) S-N Curve
d) P-T curve

Explanation: The S-N curve is the plot between the number of stress cycle and the mean stress required to fail the component at the given number of cycles. It is the most basic and useful diagram for fatigue calculation.

2. The S-N curve is the plot between the Stress and the number of cycle to failure and both are plotted in the log-log scale.
a) True
b) False

Explanation: In the S-N curve, only the number of cycle to failure are plotted in log scale. This is because the number of cycles is in order of thousands and failure pattern follow the logarithmic scale.

3. In the given S-N curve, which of the following is showing endurance limit?

a) A
b) B
c) C
d) D

Explanation: The endurance limit states that after the specified number of cycles, the material can sustain the infinite number of load reversing cycle without failure of the component. So in the case of the green line, the required stress value becomes constant after a certain point.

4. A low cycle fatigue consists of typically ________ cycles.
a) 10 cycles
b) 102 cycles
c) less than 105 cycles
d) more than 108 cycles

Explanation: There is no fine line between low cycle and high cycle fatigue, but typically less than 105 cycles. If components fail, it is kept in the category of low cycle fatigue.

5. Which of the following material does not show endurance limit?
a) Mild Steel
b) Cast iron
c) Titanium
d) Aluminum

Explanation: Generally, ferrous metal shows endurance limit below specific strain. But the non-ferrous material, in general, does not show endurance limit. The Endurance limit is also called the fatigue limit.

6. The high cycle fatigue is described by the Basquin equation.
a) True
b) False

Explanation: The high cycle fatigue is defined by Basquin equation, which states that:
-> Nσap= C; where N is the number of cycles, σa is stress amplitude, and p, C are empirical constants.

7. The fatigue limit of the material is considered after ___________ cycles.
a) 105
b) 5*105
c) 108
d) 100

Explanation: To check the fatigue limit, the material is tested for around 108 cycles at the low stress, and if the material does not fail it will be considered as the fatigue limit of the given material.

8. Among the given mechanical test, the highest number of samples are required in __________
a) tensile test
b) torsion test
c) fatigue test for S-N curve
d) fatigue test for probabilistic analysis

Explanation: The statistical analysis of fatigue sample requires the highest number of example because S-N curve can be determined by taking few samples in the range of cycle and failing them, but the probabilistic analysis needed a large number of sample to predict the chances of failure at the given stress value.

9. In the given S-N cycle, there are four different samples tested for different stress values. Among given sample, the highest probability of the failure is for __________ sample.

a) A
b) B
c) C
d) D

Explanation: The probability of failure for a sample is determined by the stress value and number of cycles. If the stress value or the amount of cycles is high, the probability of failure is also high. So in that case, the orange curve has the highest number of cycles and stress values; hence, the likelihood of failure is highest.

10. The scatter between the fatigue life data for different samples ____________ with increase in the stress value.
a) increases
b) decreases
c) remains constant
d) no relation

Explanation: As the stress values increase in the sample, the probabilities calculation for failure becomes more accurate. Or in other word, it becomes much easier to predict the failure of the sample. Hence, the scatter in the fatigue data reduces.

Sanfoundry Global Education & Learning Series – Mechanical Metallurgy.

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