This set of Materials Science Multiple Choice Questions & Answers (MCQs) focuses on “Stress and Strain”.

1. Up to which point on the stress-strain curve is Hooke’s law valid?

a) Elastic limit

b) Yield point

c) Proportionality limit

d) Fracture point

View Answer

Explanation: The proportionality limit is the point up till which the strain of an elastic body is proportional to the stress applied on it. While elastic point is the point up till which the elastic properties last. After fracture point the body breaks.

2. What is the unit for stress?

a) N/m^{2}

b) Nm^{2}

c) N/m

d) Nm

View Answer

Explanation: Stress is basically forced upon the unit area. The dimension for force is N and the dimension of area is m

^{2}. Therefore, the unit for stress is the dimension of force divided by that of area which is N/mm

^{2}.

3. Strain is a dimensionless quantity.

a) True

b) False

View Answer

Explanation: Strain is defined as the deformation produced on a body due to stress divided by a length of the body. Deformation due to longitudinal strength will have the same unit as that of length of the body therefore, strain is a dimensionless quantity.

4. Which of the following relation is stated by Hooke’s law?

a) Stress is directly proportional to stress

b) Stress is inversely proportional to stress

c) Stress is directly proportional to square of stress

d) Stress is inversely proportional to square of stress

View Answer

Explanation: According to Hooke’s law, stress is directly proportional to strain and the ratio of stress to strain is denoted by Y or E and is called Young’s Modulus oof elasticity.

5. Given the shear modulus(G) for aluminum as 2.4e^{+10} N/m^{2} and the shear strain is given as 6e^{-5}. What is the value for shear stress?

a) 13.4e+5 N/m^{2}

b) 14.4e+5 N/m^{2}

c) 12.4e+5 N/m^{2}

d) 13.4e-5 N/m^{2}

View Answer

Explanation: Shear modulus is the ratio of shear stress and shear strain. Therefore, if we simply multiply the shear modulus and shear strain we will obtain the shear stress. Hence the final answer is 2.4e

^{+10}x 6e

^{-5}which gives us 14.4e

^{+5}N/m

^{2}as the final answer.

6. Which of the following can be the value of Poisson’s ratio for an engineering structure?

a) 2

b) 0.4

c) 29

d) 100

View Answer

Explanation: The Poisson’s ratio for most of the engineering structure normally lies between 0.3 and 0.6. Therefore 2, 29, 100 cannot be valid values for Poisson’s ratio.

7. If the Poisson’s ratio is given as 0.3 and the Young’s modulus is given to 7e^{10}. What will be the value for shear modulus?

a) 2.69e10 N/m^{2}

b) 3.00e10 N/m^{2}

c) 2.59e10 N/m^{2}

d) 2.72e10 N/m^{2}

View Answer

Explanation: The relation between Young’s modulus, shear modulus and Poisson’s ratio are given by v = E/2G – 1. Taking the 1 on the left side and rearranging we get G = E/2(1+v). Inserting the values given in the question the answer comes out to be 2.69e10 N/m

^{2}. Here E=Young’s modulus, G=shear modulus and v= Poisson’s ratio.

8. Stress strain curve for cemented tungsten carbide is:

a) Hyperbola

b) Parabola

c) A curve

d) Straight line

View Answer

Explanation: The stress strain curve for cemented tungsten carbide is a straight line as being a brittle material it doesn’t have an elastic zone and therefore, it fractures after a certain load is applied.

9. Greater the angle of inclination of the stress strain curve less is the elasticity.

a) True

b) False

View Answer

Explanation: IF the angle of inclination of a stress strain curve is high, the elastic zone of the material is more as the curve starts curving after the elastic limit. Hence the elasticity of the material is high.

10. Which of the following is found out by calculating the area under the stress strain graph?

a) Toughness

b) Hardness

c) Endurance

d) Strength

View Answer

Explanation: Toughness is measured by calculating the area under the stress strain graph and is more for most ductile material than brittle material which has more toughness than ductile material.

**Sanfoundry Global Education & Learning Series – Materials Science.**

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