# Mechanical Behaviour Questions and Answers – Compressive Strength

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This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Compressive Strength”.

1. The ability of a material to withstand uniaxial compressive stress without breaking is ______
a) Tensile strength
b) Fatigue strength
c) Yield strength
d) Compressive strength

Explanation: Ability of a material to withstand compressive stress without fracturing is known as compressive strength. While in tensile strength tensile stress comes into the picture. Yield strength is the ability of a material to withstand tensile force without undergoing plastic deformation.

2. What is the compressive strength of bone?
a) 150 MPa
b) 400 MPa
c) 500 MPa
d) 2400 MPa

Explanation: Bone has a very high compressive strength of 150 MPa. Porcelain has compressive strength 500 MPa and cast iron has 400 MPa. Alumina has compressive strength 2400 MPa.

3. Which material has tensile strength higher than compressive strength?
a) Alumina
b) Silica
c) Cast iron
d) Fiberglass

Explanation: Composite materials such as fiberglass generally have the higher value of tensile strength than compressive strength. While ceramics Alumina and silica have compressive strength higher than UTS. Cast iron also shows higher compressive strength.
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4. What is the approximate ratio of tensile strength to compressive strength for most of the ceramics?
a) 1:1
b) 1:5
c) 1:10
d) 1:20

Explanation: Ceramics have compressive strength as high as 10 times the tensile strength. For example, alumina has a tensile strength 20,000 psi and compressive strength 350,000 psi. It is because ceramics are brittle in which cracks can propagate in tension but not in compression.

5. What is the compressive strength of silicon nitride?
a) 500 MPa
b) 900 MPa
c) 2400 MPa
d) 3000 MPa

Explanation: Silicon nitride is a ceramic having a very high compressive strength of 3000 MPa. 2400 MPa is a compressive strength of alumina and 500 MPa of porcelain. Steel has a compressive strength of 900 MPa.

6. Which statement is false?
a) Metals have a compressive strength ranging from 100 to 1500 MPa
b) Ceramics have a compressive strength ranging from 1000 to 5000 MPa
c) Concrete is stronger in compression than in tension
d) Concrete is reinforced with materials which provide better compressive properties

Explanation: Concrete show more strength towards compressive forces than tensile forces. To improve tensile properties, it is reinforced with materials which perform well in tension. For example, steel rods.

7. When a material is pulled in tension, it exhibits the reduction in compressive strength.
a) True
b) False

Explanation: Plastic deformation in one direction effects plastic response in another direction. This effect is known as Bauschinger effect. This causes a reduction in compressive strength.

8. For _____ value of a rate of loading, the value of strength comes out to be ______
a) Lower, lower
b) Lower, higher
c) Any, same

Explanation: If the rate of loading is slower, the value of strength measured is lower. It is because of creep. For slower loading, extra strain takes place due to creep phenomenon.

9. As the w/c ratio (mass of water/mass of cement) of concrete increases, the porosity ______ and as the result compressive strength ______
a) Increases, increases
b) Increases, decreases
c) Decreases, increases
d) Decreases, increases

Explanation: As the water content increases, porosity in concrete increases. With increasing porosity of the material, it becomes weaker. These act as fracture initiating sites.

10. Which machine is used to measure compressive strength?
a) Erichsen machine
b) Universal testing machine
c) Impact testing machine
d) Fatigue testing machine

Explanation: Universal testing machine is used to measure compressive strength. Erichsen machine is used to measure formability and Impact testing machine for Impact strength. Fatigue testing machine is used for measuring fatigue strength.

11. What is compressive stress of cylindrical specimen of diameter 2 cm and applied force is 10N?
a) 796 kN/m2
b) 450 kN/m2
c) 678 kN/m2
d) 875 kN/m2

Explanation: Compressive strength = F/A
= 10 / π (0.002)2
= 795774.72 N/m2
~ 796 kN/m2
Here F = force, A = original cross sectional area.

12. In ceramics, due to the presence of internal flaws, from which cracks can propagate in tension, but not in the compression state.
a) True
b) False

Explanation: Internal flaws as cracks and voids behave as stress raising points. These reduce the tensile strength of a material. But in case of compressive stress crack can’t propagate.

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