This set of Engineering Materials and Metallurgy Questions and Answers for Entrance exams focuses on “Elasticity, Relaxation Processes and Spring Dashpot Models”.
1. The ability of a material to return to its original state when an external force is removed is called __________
Explanation: When force is applied, materials undergo deformation. The ability of a material to resist this deformation by regaining its original state upon removal of the force is called elasticity. Plasticity is considered as the converse of elasticity.
2. The stress-strain curve can be expressed linearly by the use of _________
a) Cauchy’s principle
b) Fourier series
c) Taylor’s series
d) D’Alembert theorem
Explanation: The stress-strain curve is used to describe the elasticity of materials. This curve is generally non-linear. However, Taylor’s series may be used to express it linearly for small deformations.
3. For an isentropic material, the stress-strain relationship is known as _________
a) Bragg’s law
b) Hooke’s law
c) Lenz law
d) Sokolov-Ternov effect
Explanation: The stress-strain curve is used to describe the elasticity of materials which is generally non-linear. For an isentropic material, the linearized stress-strain relationship is called Hooke’s law.
4. Viscoelasticity exhibits which of the following properties?
c) Temperature and time dependent
d) Temperature and time independent
Explanation: Viscoelasticity differs from elasticity in that it does not completely return to its original state when the forces are removed. The viscoelastic behavior of the material is dependent on both time and temperature.
5. Which method is used for measuring the viscoelastic behavior of materials?
a) Resonant sphere technique
b) Rectangular parallelepiped resonance
c) Resonant sound resonance
d) Resonant ultrasound spectroscopy
Explanation: Broadband viscoelastic spectroscopy and resonant ultrasound spectroscopy are the two most widely preferred techniques for viscoelastic testing. These methods are preferred over the others due to their ability to be used above and below ambient temperatures and are more explicit for viscoelasticity.
Explanation: Relaxation modulus is a time-dependent elastic modulus for viscoelastic materials and is denoted by Er(t). From the equation, σ(t) is the time dependant stress, whereas ∈o is the strain.
7. The elastic component of viscoelastic material is modeled as _________
Explanation: Viscoelastic materials are those which possess the characteristics of both viscosity and elasticity. The elastic components are modeled as springs, whereas the viscous components are modeled as dashpots.
8. A series connection between a Hookean spring and a Newtonian dashpot results is ________ model.
c) Standard linear solid model
d) Prony series
Explanation: Viscoelastic materials can be modeled as springs and dashpots to understand their behavior. A connection in series of a Hookean spring and a Newtonian dashpot gives the Maxwell model, whereas parallel connection gives the Kelvin-Voigt model.
Explanation: The viscous components of viscoelastic materials are modeled as dashpots. Their stress-strain relationship is expressed by σ= η dε/dt. The elastic components that are modeled as springs are expressed by the equation σ= E∈.
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