# Mechanical Behaviour Questions and Answers – Brittle Fracture

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

1. What is cleavage plane for FCC materials?
a) {1 1 1}
b) {1 1 0}
c) {1 2 3}
d) {1 0 1}

Explanation: The cleavage plane is the plane on which crack propagation or cleavage occurs during the fracture of the crystal.

Crystal structure Cleavage plane
Face-centred materials (FCC) {1 1 1}
Body-centered structure (BCC) {1 1 0}
Hexagonal close packing (HCP) {0 0 0 1}

2. What is the cleavage plane for HCP materials?
a) {1 2 3 0}
b) {1 0 0 0}
c) {0 0 0 1}
d) {1 0 0}

Explanation: Basal planes are {0 0 0 1} in HCP metals. These planes act as cleavage planes. These fail in brittle manner in these planes.

3. Which material fails by brittle fracture?
a) White cast iron
b) Steel
c) Aluminum
d) Copper

Explanation: White cast iron consists of cementite in excess. It causes a brittle fracture. Fe3C is a brittle material because of strong bonding.

4. Which of the following materials don’t give brittle fracture?
a) White cast iron
b) Grey cast iron
c) Aluminum
d) Ceramics

Explanation: Aluminum shows a ductile fracture. White and grey cast iron and ceramics show brittle fracture. Grey cast irons have flake-like graphite which increases stress at their tips.

5. When does brittle fracture is noticed?
d) Compressing

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6. What is characteristic of brittle fracture?
a) Prior warning
b) High speed
c) Necking
d) Ductile rupture

Explanation: Brittle fracture occurs at high speed reaching to 1200 m/s in steel. It doesn’t show prior warning or necking. Ductile rupture occurs in ductile materials.

7. Fracture always occurs above yield stress.
a) True
b) False

Explanation: Brittle fracture occurs at a lower stress level than yield stress. It causes fracture without plastic deformation. This phenomenon is catastrophic.

8. In ____ fracture, crack is unstable and propagates rapidly.
a) Ductile
b) Brittle
c) Shear
d) Tensile

Explanation: In brittle fracture, crack is said to be unstable. It propagates at high speed. Its propagation doesn’t require an increase in stress level.

9. Brittle fracture is a break in a brittle piece of metal that failed because stress exceeds _____
a) Cohesion
c) Yield stress
d) Tensile stress

Explanation: When stress exceeds the cohesion, brittle fracture occurs. It occurs below yield stress. It occurs at a lower level of stress.

10. Which of the followings is not a type of fracture in brittle materials?
a) Bright granular
b) Flat type
c) Neck
d) Chevron patterns

Explanation: Brittle fracture appears bright granular. It looks the flat type. Chevron patterns may be present.

11. The crack may be __________ and ____________ depending on strength of grain boundaries.
a) Brittle, ductile
b) Trans granular, intergranular
c) Shear, cleavage
d) Fibrous, granular

Explanation: Depending on strength of grain boundaries, fractures are of two types. These are trans granular and intergranular. While on the basis of appearance, fibrous and granular fracture.

12. In intergranular fracture, crack travels along grain boundaries.
a) True
b) False

Explanation: Crack travels along grain boundaries in intergranular fracture. It occurs when the grain boundary is weak and brittle. Cracks don’t pass through the actual grains.

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