This set of Aerospace Materials and Processes Multiple Choice Questions & Answers (MCQs) focuses on “Aircraft Materials – Fatigue Test”.
1. What is fatigue stress?
a) The stress endured by an observer
b) Stress divided by strain and multiplied by conductivity
c) The amount of stress, a material can tolerate repeatedly without failure
d) The stress endured perpendicular to the observer
View Answer
Explanation: The fatigue stress of a material is the stress it can tolerate several times, without resulting in any failure. Each material has that fatigue stress and if it is crossed it is unsafe to load the material frequently.
2. Testing a material to know it’s fatigue strength is very easy.
a) True
b) False
View Answer
Explanation: The statement is not true. It is not at all easy to determine the fatigue stress of a material. In fact, it is so difficult and consuming that there are lots of materials whose fatigue strength has not been found.
3. The amount of test cycles required to find out the fatigue stress of hard steels is ___________
a) 10,000,000
b) 2600
c) 26
d) 2,000,000
View Answer
Explanation: Performing a fatigue test on a material is a very difficult task. The amount of test cycles required to be performed on hard steels is 2,000,000. For soft steels, the number of cycles required is 10,000,000.
4. Which of the following is a fatigue-testing apparatus?
a) Rotating-beam tests
b) Load test
c) Fixed load test
d) Rotating wing test
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Explanation: There are several different types of fatigue testing apparatus available to test materials or specimen. But the most widely used apparatus is rotating-beam tests also called as rotating-cantilever tests.
5. The amount of test cycles required to find out the fatigue stress of hard aluminium alloys is ____________
a) 64,000,900,000
b) 500,000,000
c) 3000
d) 27
View Answer
Explanation: A huge number of test cycles are required to determine the fatigue strength of a material. The number of cycles required for aluminium alloys is 500,000,000. It is the same for magnesium alloys as well.
6. What is the typical speed of rotation in a normal speed fatigue testing machine?
a) 2000 rpm
b) 20 rpm
c) 26,000 rpm
d) 14,000 rpm
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Explanation: The speed of rotation of fatigue testing machines is different for different machines. But, the typical speed is usually of the order of 2000 rpm. For machines that are high speed, it can be 12,000 rpm.
7. What is the diameter of a typical specimen used in fatigue testing?
a) 2000 inches
b) 0.0005 inches
c) 1 inch
d) 26 inches
View Answer
Explanation: Specimen of fatigue tests are typically rolled or forged bar stock. The are one inch in diameter. They can vary depending on the requirements and the material being tested to determine fatigue strength.
8. The specimen of fatigue testing must not have ___________
a) Uniform cross-section
b) Metal
c) Certain colours
d) Notches and holes
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Explanation: It is necessary that the specimen being tested to determine fatigue strength not have notches and holes in it. The specimen is usually cylindrical rods that do not contain any of the above defects.
9. Corrosion of materials results in ___________ of fatigue limit.
a) reduction
b) increment
c) double
d) satisfaction
View Answer
Explanation: Corrosion of a material is not a desirable quality. This is because even a small amount of it can cause a reduction of fatigue limit. Even flaws like lack of uniform cross-section in the specimen can have the same effect.
10. Materials that have been subjected to heat treatment generally have lower tensile strengths than materials that are annealed.
a) True
b) False
View Answer
Explanation: This statement is not true. Materials that have been subjected to heat-treatment have higher tensile strengths, (not lower) compared to materials that are annealed. They also have higher fatigue limits.
11. The fatigue limit of a specimen is ___________ of its fatigue range.
a) triple
b) double
c) half
d) exactly the same
View Answer
Explanation: The fatigue limit of a specimen or material is half of its fatigue range. The fatigue value of a material also depends on load, but it will typically be in the fatigue range for materials or specimen.
12. The fatigue limit of steel is around ____ times the ultimate tensile strength.
a) 0.3
b) 5
c) 3
d) 0.5
View Answer
Explanation: The fatigue limit is different for different materials. For the material steel, the fatigue limit is around 0.5 of its ultimate tensile strength. For materials that are non-ferrous in nature, the fatigue limit can 0.3 or 0.4 of its ultimate tensile strength.
Sanfoundry Global Education & Learning Series – Aerospace Materials and Processes.
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