This set of Mechanical Metallurgy Questions and Answers for Entrance exams focuses on “Tension Test – Effect of Strain Rate on Flow Properties – 3”.
Explanation: As the temperature increases, the strength decreases and the ductility increases. So the green curve has the highest ductility and least strength. Similarly, the orange curve has the highest strength and least ductility.
2. In the case of the FCC metal, the yield strength is more temperature-dependent than the tensile strength of the given metal.
Explanation: In the case of FCC metal the tensile strength is more temperature-dependent than the yield strength of the material, that is why the engineering stress-strain curve gets flat at a higher temperature in FCC metal.
3. The homologous temperature is defined as of __________
a) melting point/test temperature
b) test temperature/melting point
c) 0.5 * melting
d) 2*test temperature
Explanation: The homologous temperature is defined as the ratio of the test temperature to melting point temperature of the material. This is generally used to calculate the high-temperature properties of the different materials.
4. The relationship between the flow stress and the strain rate is given in empirical form ______ where strain rate=ϒ, σ = flow stress, C & m = constant.
Explanation: The relationship between the strain rate and flow stress is given as:
σ=Cϒm; where C and m are constants.
m is known as the strain rate sensitivity. It is obtained by the slope of the log σ and log ϒ curve.
5. The relationship between the stress and strain rate is given as σ=Cϒm, where m is strain rate sensitivity. The strain rate sensitivity _____________ with increase in temperature.
c) remains constant
d) no relationship
Explanation: As the temperature increases, the dependence of the flow curve on the strain rate increase which leads to an increase in the strain rate sensitivity of the material with an increase in temperature.
6. The strain rate sensitivity of metal is in the range of __________ at room temperature.
Explanation: The strain rate sensitivity of the metal is quite low, which is generally less than 0.1 at room temperature. As the temperature increases, the strain rate sensitivity also increases.
7. The strain rate sensitivity in a Newtonian viscous solid is _______
Explanation: The Newtonian solid are high superplastic materials where the strain rate sensitivity is equal to 1. So the relation will be:
8. When the strain rate sensitivity is equal to 1. The cross-sectional area of sample will _________ on applying load.
c) remain constant
d) no relationship
Explanation: In the case of m=1, the material follows the Newtonian solid rule, and necking is avoided in the material. So material can be stretched for prolong period without necking, and the cross-sectional area remains the same.
9. A screw-driven constant head velocity machine for tensile testing machine are _________
a) load controlled machine
b) displacement controlled machine
c) stress controlled machine
d) modulus controlled machine
Explanation: A mechanical screw controlled machine with constant head velocity, have only freedom of having a uniform elongation of the sample. So, it is called strain-controlled or displacement controlled machine.
Sanfoundry Global Education & Learning Series – Mechanical Metallurgy.
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