This set of Aerospace Materials and Processes Multiple Choice Questions & Answers (MCQs) focuses on “Aircraft Materials – Hardness testing – Brinell and Rockwell Hardness”.
1. Which of the following is not a hardness testing method?
a) Rockwell hardness
b) Brinell hardness
c) Set method hardness
d) Shore scleroscope hardness
View Answer
Explanation: Hardness testing methods are processes to check the strength of the material. Rockwell hardness, Brinell hardness, Shore scleroscope hardness and Diamond pyramid hardness are typically used hardness tests. The set method is one of the methods used to determine the yield strength of a material.
2. It is vital that surfaces that have to be tested to determine the hardness of the material must be free of _____
a) ridges
b) evenness
c) smoothness
d) thickness
View Answer
Explanation: In order to perform tests on the material, it must meet certain standards. It should have the required thickness to avoid bulging and must be free of ridges and scratches. It should be even and smooth.
3. It is impossible to find a relation between hardness and tensile strength.
a) True
b) False
View Answer
Explanation: There is a relation between the hardness and tensile strength. The approximate value of the tensile strength of several materials can be found when the hardness of those materials is known.
4. For ____________ materials, there is no correspondence between tensile strength and hardness.
a) soft
b) hard materials
c) steel
d) carbon
View Answer
Explanation: There is a relation between hardness and tensile strength for materials like carbon and low alloy steels. The tensile strength can be predicted using hardness values. But for comparatively soft materials like aluminium alloys, this is not applicable.
5. There is a necessity to find the hardness of a material without causing deformation in them.
a) True
b) False
View Answer
Explanation: There is a necessity to find the hardness of a material as it can give an indication of the strength and several other properties of a material. At the same time, it is important to avoid damaging the material as that would be a loss. Especially for a manufactured material.
6. The Brinell testing method uses a steel ball of __________ diameter for testing purposes.
a) 26mm
b) 1mm
c) 10m
d) 10mm
View Answer
Explanation: The Brinell test method involves pressing a hard ball made of steel, with a particular pressure onto the surface of the test specimen. The diameter of the steel ball being used is 10 mm.
7. In the Brinell testing method, the load should be pressed for a minimum of ____________
a) 1000 seconds
b) 60 seconds
c) 10 seconds
d) 3 seconds
View Answer
Explanation: In the Brinell testing method, the test specimen is indented with a ball made of steel, with a diameter or 10 mm for a certain amount of time. The minimum time period is 10 seconds before the load is released.
8. If the load being applied is 2000kg, and the area of impression is 250 Square millimetres, what is the Brinell number of the test material?
a) 80 kg per square millimeter
b) 25 kg per square millimeter
c) 20 kg per square millimeter
d) 8 kg per square millimeter
View Answer
Explanation: Brinell hardness number = \(\frac{Load \,Applied}{Area \,of \,impression \,(spherical)}\)
= \(\frac{2000}{250}\)
= 8 kg per square millimeter.
9. Which of the following is not a way to prepare the test material for the Brinell hardness test?
a) Grinding
b) Layering
c) Filing
d) Polishing
View Answer
Explanation: The requirements of the specimen for Brinell testing method is similar to the remaining test methods. There are several ways to prepare the material for the test. Grinding, filing and polishing using emery paper are done. Layering is not one of the methods.
10. To perform Brinell test on a soft material like bronze _____________ kg of load is applied on the specimen.
a) 3000
b) 500
c) 6600
d) 1200
View Answer
Explanation: Different amount of load are applied on test specimen depending upon the type of material being tested. For steel testing, the pressure applied is 3000kg. For comparatively softer materials like aluminium alloys, the pressure applied is 500kg.
11. Rockwell hardness test uses either a ____________ ball or ___________ cone for measuring hardness.
a) steel, diamond
b) diamond, steel
c) carbon, iron
d) iron, carbon
View Answer
Explanation: Rockwell hardness value is found by calculating the penetration of either a steel ball or diamond cone under a particular load. The Rockwell hardness number appears on the dial of the machine.
12. The Rockwell hardness testing method typically uses certain amounts of load. Which of the following is not one of the loads used?
a) 150kg
b) 60kg
c) 5kg
d) 100kg
View Answer
Explanation: The loads being applied in the Rockwell hardness method usually on the penetrator(steel ball or diamond cone) being used and the test specimen. The loads applied are typically 100kg, 150kg and 60kg.
13. To find a true hardness reading for hard steel, the minimum thickness required for material is ____
a) 0.0027mm
b) 6.858mm
c) 0.27mm
d) 234mm
View Answer
Explanation: To obtain the Rockwell hardness value, the loads used or penetrators depends on the weather the material is soft or hard. The minimum thickness required for hard steel is 6.858mm. This will give an accurate hardness value.
14. In the beginning of the Rockwell hardness experiment, the reading dial is set to _____
a) 100
b) 50
c) 0.1
d) 0
View Answer
Explanation: The dial on the Rockwell hardness test method is where the value can be found. There are two sets of numbers on the dial, black and red. Before the major load is applied on the test specimen, the direct reading dial on the machine has to be fixed to zero.
15. Which of the following hardness testing method is preferred for aircraft manufacturing purposes?
a) Brinell hardness
b) Rockwell hardness
c) Divider method
d) Shore scleroscope hardness
View Answer
Explanation: The method of hardness testing usually preferred for aircraft manufacturing purposes is the Rockwell hardness method. This is because it is easy to operate and is reliable. Divider method is used to determine the yield point of a material. It is not a hardness testing method.
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