# Mechanical Behaviour Questions and Answers – Fatigue Test

This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Fatigue Test”.

1. In what terms, fatigue life is measured?
a) Time of failures
b) Number of cycles of failure
c) Stress of failure
d) Appearance of fracture

Explanation: Fatigue life is measured in terms of the number of cycles of failure. The maximum stress is kept fixed.

2. Fatigue curves are popularly known as __________ curves.
a) S
b) R
c) N
d) S-N

Explanation: Fatigue curves are popularly known as S-N curves. S stands for stress and N stands for the number of cycles. The number of cycles is taken as log N.

3. What term is used for the maximum stress at which material fail on a specified number of cycle?
a) Fatigue strength
b) Fatigue life
c) Ultimate tensile strength
d) Endurance limit

Explanation: The maximum stress at which material fail on a specified number of cycle is fatigue strength. Many materials exhibit a limiting stress value. Below this, it can be operated for the indefinitely large number of cycles.

4. Word “endurance limit” is used for _____________
a) Plastics
b) Ferrous materials
c) Nonferrous materials
d) Alloys

Explanation: Endurance limit is used for nonferrous materials. These don’t show a clear fatigue limit. While ferrous materials show fatigue limit.

5. Which ferrous material doesn’t show fatigue limit?
a) Cast iron
b) Wrought iron
c) Austenitic stainless steel
d) Low carbon steel

Explanation: All ferrous materials show fatigue limit. These are cast iron, wrought iron and high and low carbon steels. Austenitic stainless steel is an exception.

6. Which of the following show a fatigue limit?
a) Titanium
b) Cast iron
c) Magnesium
d) Al-Mg alloys

Explanation: Cast iron being a ferrous material, shows fatigue limit. Titanium and Magnesium metals don’t show it. Al-Mg alloys don’t show fatigue limit either.

7. What is the reason for fatigue failure?
a) Movement of Dislocations
b) Submicroscopic cracks
c) Dynamic recovery
d) Vacancy coalescence

Explanation: Fatigue failure occurs due to submicroscopic cracks. These develop on the surface of a material. These eventually coalesce into visible crack.

8. What cycles range is chosen for endurance limit?
a) 102 – 103
b) 105 – 106
c) 107 – 108
d) 1011 – 1012

Explanation: In nonferrous materials, non-effective fatigue limit is shown. The stress corresponding to 107 – 108 cycles is taken as endurance limit.

9. What is the relation between stress at the tension side and diameter of the fatigue test specimen?
a) σt α d
b) σt α d2
c) σt α 1/d2
d) σt α 1/d3

Explanation: σt = 32M /πd3 Here, σt is stress at the tension side and d is the diameter of specimen. M is bending moment.

10. Magnitude of compressive stress on the fatigue test specimen is ___ tensile stress magnitude.
a) Equal to
b) Greater than
c) Lesser than
d) Changes with weight

Explanation: As bending moment is kept same, so the magnitude of compressive and tensile stress is equal. Compressive stress has a negative sign to differentiate.

11. Endurance limit has unit Kgf.
a) True
b) False

Explanation: Endurance limit is maximum alternating stress that a material can endure for special cycles. Its unit is Kgf mm-2.

12. Nylon has a linear S-N curve.
a) True
b) False

Explanation: Some plastics show no indication of a fatigue limit. Their S-N curves are linear. Examples are nylon, Polyethylene etc.

Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.

To practice all areas of Mechanical Behaviour & Testing of Materials, here is complete set of 1000+ Multiple Choice Questions and Answers.

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