This set of Mechanical Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Tension Test – Notch Tensile Test”.
1. If the crosshead of the tensile testing machine is moving with constant velocity v, then after time t, the total displacement of crosshead will be vt. A specimen is held between the crosshead of the machine. The total displacement in the sample will be ______________
a) more than vt
b) less than vt
c) equal to vt
d) indeterminate
View Answer
Explanation: The total displacement in the crosshead of the machine is caused by:
-> Elastic displacement of the machine
-> Elastic displacement of the specimen
-> Plastic displacement of the specimen
So if the total displacement is specimen alone, it will be less than crosshead displacement.
2. The hard and soft tensile testing machine is defined based on the __________
a) the hardness of the sample
b) the hardness of the floor on which it is installed
c) by the stiffness/spring constant of the machine
d) by the stiffness/spring constant of the specimen
View Answer
Explanation: There is a great deal of difference between the device and sample tested in the machine. This difference gives discrepancy in results and sometimes will tend to miss useful information. The screw-driven machine is “hard machine”, and the hydraulically driven machine is “soft machine”.
3. A hard testing machine will produce the upper and lower yield point faithfully.
a) True
b) False
View Answer
Explanation: A hard device with high spring constant gives correct prediction of upper and lower yield point. The soft machine tends to smear the yield points, and extension of the constant load will be recorded.
4. The Zener-Hollowman parameter is used in defining a ___________
a) constitutive equation of plastic deformation
b) relationship between the state of stress and strain rate
c) relationship between the state of strain and strain rate
d) relationship between the elastic and plastic deformation
View Answer
Explanation: The constitutive equation is the idea of deriving a general equation considering strain, strain rate, and temperature for any state of plastic deformation. It is like in thermodynamics where the state of the system can be defined by pressure, temperature, and volume.
5. The Zener-Hollowman (Z) is equal to ___________
Where ϒ-strain rate, ε-strain, σ-stress, T-temperature, ΔH-activation energy, R- universal gas constant.
a) σ*exp(-ΔH/RT)
b) ε*exp(-ΔH/RT)
c) ϒ*exp(-ΔH/RT)
d) exp(-ΔH/RT)
View Answer
Explanation: The constitutive it uses the Zener-Hollowman parameter to find the relationship and predict the constitutive equation of the plastic deformation of the material.
6. The stress-relaxation test uses the concept of predicting the reduction in internal stress with time.
a) True
b) False
View Answer
Explanation: The idea is to keep the sample at constant strain and measure the change in the stress with the change in time.
7. Which of the following can be used as a notch test sample for standard test?
a)
b)
c)
d)
View Answer
Explanation: The notch test is done on a sample having a 60-degree notch on the sample on one of the side edges and the impact is applied from another side of the groove.
8. The notch strength is defined as the ___________
a) maximum load/Maximum cross-sectional area
b) minimum load/notch cross-sectional area
c) maximum load/notch cross-sectional area
d) average load/average cross-sectional area
View Answer
Explanation: The Notch strength is defined as the maximum load on the sample divided by the minimum area (which is eventually the notch area in this case).
9. The notch strength ratio is defined as ____________
a) maximum load for the notched specimen/tensile strength for un-notched specimen
b) tensile strength for un-notched specimen/maximum load for the notched specimen
c) minimum load in notch specimen/minimum load in the un-notched specimen
d) maximum load in notch specimen/maximum load in the un-notched specimen
View Answer
Explanation: The notch strength considers the area of minimum cross-section, so the strength values are generally higher than the tensile strength of the material. So to deal with this, ratio of the maximum load from notch specimen to tensile strength in the un-notched specimen is taken for the calculation.
10. The Notch strength ratio is ________________ for brittle notch.
a) more than 1
b) less than 1
c) equal to 1
d) less than 0
View Answer
Explanation: The NSR is defined as
-> Maximum load for the notched specimen/ tensile strength for un-notched specimen
So for the brittle notch, the tensile strength for the un-notched sample is always greater than the maximum load on the notched specimen, because it fails before reaching to the tensile strength point of the un-notched specimen.
11. As the temperature increases, the difference between the strength of a notched sample and un-notched sample ____________
a) increases
b) decreases
c) remains constant
d) cannot be determined
View Answer
Explanation: The ductility of the material increases with increases in temperature; this results in reducing the impact of notching during the test. Hence the difference in the strength of notch specimen to unnotched specimen decreases with an increase in temperature.
12. As the carbon content in the steel increases __________
a) strength increases and ductility decreases
b) strength and ductility decreases
c) strength and ductility increases
d) ductility increases and strength decreases
View Answer
Explanation: As the carbon content increases, the amount of cementite in the matric increases. This increases the strength of the material. As it is a hard phase, it reduces the ductility.
Sanfoundry Global Education & Learning Series – Mechanical Metallurgy.
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