# Mechanical Metallurgy Questions and Answers – Fatigue of Metals – S-N Curve – 1

This set of Mechanical Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Fatigue of Metals – S-N Curve – 1”.

1. In the given stress cycle, the range of stress is equal to ________ a) A
b) B
c) C
d) D

Explanation: The range of stress is given as
-> σmaxmin
-> In this case, the magnitude of the minimum and maximum stress is equal, but in the opposite direction, so the range of stress will be equivalent to D.

2. In the given stress cycle, the alternating stress is equal to ________ a) A
b) B
c) C
d) D

Explanation: The alternative stress is equal to half of the range of stress. So
-> (σmaxmin)/2
In this case, it will be similar to A.

3. The mean stress is indicated by which point in this stress cycle? a) A
b) B
c) C
d) D

Explanation: The mean stress is always equal to:
-> (σmax+ σmin)/2
So, in this case, the minimum and the maximum have a similar magnitude and opposite direction.
max+ σmin)=0
So mean stress will be equal to zero.

4. In the following stress cycle, the stress amplitude is indicated by which point in this curve? a) A
b) B
c) C
d) D

Explanation: The stress amplitude is already defined as half of the range of stress:
-> (σmaxmin)/2
-> In this case, it is equal to C.

5. Find the mean stress in the given stress cycle? a) 30 MPa
b) 50 MPa
c) 60 MPa
d) 10 MPa

Explanation: The mean stress is given as the
-> (σmaxmin)/2
-> σmax=50 MPa
-> σmin=10 MPa
-> (50+10)/2=30 MPa.
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6. Find the range of stress in the given stress cycle? a) 30 MPa
b) 50 MPa
c) 40 MPa
d) 10 MPa

Explanation: The range of stress is equal to:
-> (σmaxmin)
-> 50-10 = 40 MPa.
Explanation: In the given curve, the minimum stress is equal to zero.
-> Mean stress=(σmaxmin)/2
-> Alternating stress=(σmaxmin)/2
As σmin=0, the values for both the mean and alternating stress will be equal to zero.

8. During a cycling loading of the stress, which of the following value cannot be equal to zero?
a) Mean pressure
b) Minimum stress
c) Maximum stress
d) Range of stress

Explanation: The scope of stress is a magnitude of difference between the minimum and maximum stress. So, for a cyclic loading of stress, it cannot be equal to zero. It has to be a positive number.

9. The stress ratio is defined as the ________
a) σmaxmin
b) σmaxmin
c) σminmax
d) σmaxmin

Explanation: The stress ratio is generally denoted by R and is always equal to:
-> σminmax.

10. The amplitude ratio is defined as the ___________
a) σmaxmin
b) σmeanamplitude
c) σamplitudemean
d) σmaxmin

Explanation: The amplitude ratio is the ratio between the stress amplitude to the mean stress value of the cycle loading curve.

11. If the stress ratio is given by R, and the amplitude ratio is given by A, the ratio between the R and A is given as __________
a) A=R
b) A=1/R
c) A=(1-R)/(1+R)
d) A=(1+R)/(1-R)

Explanation: The amplitude ratio is given as:
-> σamplitudemean
So the relationship between them is:
A= σamplitudemean = (1-R)/(1+R).

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