# Mechanical Behaviour Questions and Answers – Impact Strength

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

1. _____ is the ability of a material to sustain impact forces without fracture.
a) Impact strength
b) Toughness
c) Tensile strength
d) Compressive strength

Explanation: Impact strength is the ability of a material to withstand impact load without fracture. Toughness is the resistance against fracture. Tensile strength is a static mechanical property.

2. Moisture absorption causes ___ in impact strength and ___ in the strength of polymers.
a) Increase, Increase
b) Increase, decrease
c) Decrease, Increase
d) Decrease, decrease

Explanation: Moisture acts as a plasticizer in the polymer. So it reduces its strength. But impact toughness of polymer increases.

3. What is Izod impact energy of Nylon 6/6?
a) 10-50 J/m
b) 12-20 J/m
c) 50-100 J/m
d) 100-210 J/m

Explanation: Nylon 6/6 has a high impact energy of 50-100 J/m. Epoxy has Izod impact energy of 10-50 J/m. Urea formaldehyde and ABS have an impact strength of 12-20 and 100-210 J/m respectively.

4. Which factor increases impact toughness?
a) Cold working
b) Quench Hardening
c) Water absorption in polymer
d) Notches

Explanation: Water absorption in polymer improves impact strength. Cold working and precipitation hardening makes material brittle hence decrease impact strength. Presence of notch increases stress intensity, decreasing impact toughness.

5. What is izod impact energy of poly-carbonates?
a) 53 J/m
b) 10-50 J/m
c) 430-850 J/m
d) 12-20 J/m

Explanation: Polycarbonates have high impact strength 430-850 J/m. Polypropylene has an impact strength of 53 J/m. Epoxy and urea formaldehyde have an impact energy of 10-50 and 12-20 J/m respectively.
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6. Cleavage in bcc materials take place along ___ plane.
a) {001}
b) {110}
c) {123}
d) {112}

Explanation: A cleavage plane is the fracture of a crystal by crack propagation. It is {001} for bcc. It is different for different crystal structures.

7. Brittle fracture needs more energy than the ductile fracture.
a) True
b) False

Explanation: Ductile fracture needs more energy than a brittle fracture. In ductile fracture, some plastic deformation takes place before fracture. That’s why it needs more energy.

8. Ductile-brittle transition temperature increases with strain rate.
a) True
b) False

Explanation: As Strain rate increases, materials show brittleness. That’s why ductile-brittle transition temperature increases.

9. Which statement is false according to impact strength?
a) Notch serves as a stress concentration zone
b) Lowering the temperature reduces the impact strength in BCC materials
c) Generally, strong metals have a lower impact strength
d) In polymers, impact strength keeps on the increase with temperature

Explanation: Polymers show ductile brittle transition. So impact strength improves with temperature. But at higher temperatures, due to softening, impact strength decreases.

10. What is the cross section of izod test specimen?
a) 10×10 mm
b) 10×12 mm
c) 12×12 mm
d) 8×10 mm

Explanation: Izod test specimen’s cross section is kept standard at 10×10 mm. It is the same for charpy test. It is kept standard so as to avoid the effect of dimensions.

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