# Machine Design Questions and Answers – Fluctuating Stresses & Fatigue Failure

This set of Machine Design Questions & Answers for freshers focuses on “Fluctuating Stresses & Fatigue Failure”.

1. The stress represented by sin (t) + 1 belongs to which category?
a) Fluctuating Stresses
b) Alternating stresses
c) Repeated Stresses
d) Reversed Stresses

Explanation: The minimum stress value is zero and hence is belongs to Repeated Stress category.

2. The stress represented by sin (t) + 2 belongs to which category?
a) Fluctuating Stresses
b) None of the mentioned
c) Repeated Stresses
d) Reversed Stresses

Explanation: The mean as well as the amplitude value is non zero hence it belongs to Fluctuation Stress Category.

3. The stress represented by sin (t) + 4 belongs to which category?
a) Alternating Stresses
b) None of the mentioned
c) Repeated Stresses
d) Reversed Stresses

Explanation: The mean as well as the amplitude value is non zero hence it belongs to Alternation Stresses category which is the other name of Fluctuation Stresses.

4. The stress represented by cos (t) belongs to which category?
a) Fluctuating Stresses
b) Alternating Stresses
c) Repeated Stresses
d) Reversed Stresses

Explanation: Half cycle is in tensile stress and other half in compressive stress, hence it belongs to Reversed Stresses Category.

5. If the mean stress value for a sinusoidal stress function is zero, then this type of stress falls in which category?
a) Fluctuating Stresses
b) Alternating Stresses
c) Repeated Stresses
d) Reversed Stresses

Explanation: If mean is to be zero, then there must be compressive as well as tensile stresses and hence belongs to reversed stresses category.
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6. The phenomenon of decreased resistance of the materials to fluctuating stresses is the main characteristic of _____ failure.
a) Fracture
b) Fatigue
c) Yielding
d) None of the mentioned

Explanation: Fatigue failure of the material is the failure at low stress levels under fluctuating syresses.

7. Fatigue failure is time dependent failure.
a) True
b) False

Explanation: Fatigue failure is defined as time delayed fracture under cyclic loading.

8. There is sufficient plastic deformation prior to fatigue failure, which gives a warning well in advance.
a) True
b) False

Explanation: Fatigue cracks are not visible until they reach the surface and by that time the failure has already taken place. Material nevers enters in the plastic range.

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