# Mechanical Metallurgy Questions and Answers – Brittle Fracture and Impact Testing – Instrumented Charpy Test

This set of Mechanical Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Brittle Fracture and Impact Testing – Instrumented Charpy Test”.

1. Which of the following is not among the basic condition responsible for causing the fracture of brittle?
a) A triaxle state of stress
b) Low temperature
c) High strain rate
d) Large sample width

Explanation: The brittle fracture is mainly caused by triaxle state of stress, low temperature and high strain rate. There is no direct impact of sample width on nature of failure of the material.

2. In both the Charpy and Izod impact testing, the load is applied from the backside on notch for causing fracture.
a) True
b) False

Explanation: In Charpy impact test, the load is applied from backside of the crack, while in Izod test, the load is applied from front side of the crack. Both result in similar kind of output data.

3. The maximum plastic stress concentration accumulated at the crack tip, is given by ________ (where w is the included flank angle of the notch).
a) Kσ=[1+(π/2)-(w/2)]
b) Kσ=[1+(π/2)+(w/2)]
c) Kσ=[1+(π/2)(w/2)]
d) Kσ=[1-(π/2)-(w/2)]

Explanation: The impact tests result in the state of triaxle stress on the notch, the maximum value of stress at the crack tip which can be achieved is equal to Kσ=[1+(π/2)-(w/2)].

4. The principle result in the impact test is the energy absorbed in the fracturing of the sample.
a) True
b) False

Explanation: The main idea behind the impact test is, amount of energy absorbed in breaking the sample. The ductile the fracture, higher will be the absorbed energy. So after breaking, the distance the hammer travels decides the amount of energy absorbed in the impact.

5. The nature of fracture in charpy test is not determine by __________
a) distance hammer travelled after impact
b) appearance of the fracture surface
c) the amount of energy absorbed

Explanation: The appearance of the surface has a lot to decide based on the texture of surface. If it is fibrous it is ductile, if it is granular it is brittle in nature. The type of loading has impact on fracture behaviour, but does not tell about the percentage of ductile or brittle nature of the fracture.

6. The relation between amount of energy absorbed and test temperature is shown by curve _____

a) A
b) B
c) C
d) D

Explanation: The amount of energy absorbed sharply drop as the temperature decreases. There is range of temperature over which this transformation from ductile to brittle takes place and known as the DBTT point.

7. The given absorbed energy vs temperature graph shows the curve for different types of material. Which of the following shows the curve for FCC material?

a) A
b) B
c) C
d) D

Explanation: The FCC material generally fractures in ductile manner, so the energy absorbed is high, but FCC material does not show any ductile to brittle transition, so the variation of absorbed energy with change in temperature is minimum.

8. The given absorbed energy vs temperature graph shows the curve for different types of material. Which of the following shows the curve for BCC material?

a) A
b) B
c) C
d) D

Explanation: The BCC material fails in ductile manner at higher temperature, but as the temperature reduces the fracture becomes brittle in nature, so there is sharp transition from ductile to brittle fracture in BCC.

9. The given absorbed energy vs. temperature graph shows the curve for different types of material. Which of the following shows the curve for high-strength material?

a) A
b) B
c) C
d) D

Explanation: The high strength material have exceptionally high strength, but they are brittle in nature. So they have low impact absorbed energy, also they don’t show the ductile to brittle transition.

10. Which of the following material has highest tendency for ductile to brittle transition?
a) FCC
b) HCP
c) BCC
d) DBTT does depends on crystal structure

Explanation: The BCC has highest tendency for DBTT, because BCC has 48 independent slip system at room temperature. As the temperature decreases, the number of independent slip system reduces, so the nature of fracture becomes brittle.

11. The ductile to brittle transition temperature in metal is around ____ of melting point (Tm)?
a) 0.1 Tm
b) 0.5 Tm
c) 0.9 Tm
d) 0.0001 Tm

Explanation: The ductile to brittle transition temperature is generally below the room temperature for metals. By considering the melting point, the DBTT comes around 0.1 of melting point of given metal.

12.The ductile to brittle transition temperature in ceramic is around ____ of melting point (Tm)?
a) 0.1 Tm
b) 0.5 Tm
c) 0.9 Tm
d) 0.0001 Tm

Explanation: The ceramic are generally brittle in nature at room temperature, hence the ductile to brittle transition temperature must be above the room temperature. For most of the ceramics, it comes around 0.5Tm

13. The fracture transition plastic (FTP) point is defined as __________
a) point where fracture is 100% brittle
b) point where fracture is 100% ductile
c) point where fracture is 50% brittle and 50% ductile
d) point above which the fracture is 100% ductile

Explanation: There are many criteria given to decide the appropriate point where ductile to brittle transition occurs. In FTP, this point is defined as the point above which the fracture is 100% fibrous in nature.

14. The fracture appearance transition temperature (FATT) point is defined as the _______
a) point where fracture is 100% brittle
b) point where fracture is 100% ductile
c) point where fracture is 50% brittle and 50% ductile
d) point above which the fracture is 100% ductile

Explanation: This point is arbitrarily defined and most of the times used for practical application. This is point where the fracture is 50% cleavage and 50% shear. Or in other terms 50% ductile and 50% brittle in nature.

15. The nil ductility temperature (NDT) was used in world war-II for analysis of breaking ship. The NDT is defined as the ______
a) maximum temperature where fracture is 100% brittle
b) minimum temperature where fracture is 100% ductile
c) maximum Temperature where fracture is 50% brittle and 50% ductile
d) maximum Temperature above which the fracture is 100% ductile

Explanation: The nil ductility point is defined as the maximum temperature at which the fracture is 100% cleavage in nature and below this point, there is absolutely no ductility observed in the metal. From design point of view this is an important point.

Sanfoundry Global Education & Learning Series – Mechanical Metallurgy.

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