---
title: "Short note: fracture mode of materials"
subject: "Civil Engineering Materials"
chapter: 1
key: "semester_3/civil_engineering_materials:fracture-mode-materials"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/fracture-mode-materials
site: BCT Engineering
---

# Short note: fracture mode of materials

Civil Engineering Materials · Chapter 1: Introduction to Civil Engineering Material

- Asked in: 2057 Chaitra (old course), 4 marks
- Video: [Definition of Fracture and Modes of Fracture - Fracture Mechanics - Strength of Materials](https://www.youtube.com/watch?v=IscPV-lq-kk) — Ekeeda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/fracture-mode-materials
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-1

## Question

Write a short note on fracture mode of materials.

## Short answer

Ductile fracture occurs after extensive plastic deformation and necking, with a dull fibrous surface and high energy absorption. Brittle fracture is sudden with little deformation, a flat bright surface and low energy. Low temperature, high strain rate, and notches promote brittle fracture.

## Answer

**Fracture** is the separation of a body into two or more parts under stress. There are two main modes.

#### Ductile fracture
- Occurs after extensive plastic deformation and necking.
- Absorbs a lot of energy and gives warning.
- The surface is dull and fibrous, with a cup-and-cone shape in tension.
- Mechanism: voids form in the neck and join up, and the remaining rim shears at 45 degrees. Examples: mild steel, aluminium.

#### Brittle fracture
- Occurs suddenly with very little or no plastic deformation.
- The crack grows extremely rapidly, absorbing little energy.
- The surface is flat, bright and granular, perpendicular to the tensile stress.
- It occurs by cleavage (breaking of atomic bonds along crystal planes) or along grain boundaries. Examples: cast iron, glass, concrete, steel at low temperature.

#### Other modes
Fatigue fracture (cyclic loading) and creep fracture (long-term loading at high temperature).

Factors that promote brittle fracture: low temperature, high strain rate, and notches and sharp corners (stress concentration).

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Ductile fracture surface is
   A. dull, fibrous, cup-and-cone
   B. flat and bright
   C. granular and flat
   D. glassy
   Answer: A. Ductile. (Key point: Ductile)

2. Brittle fracture occurs by
   A. void coalescence
   B. cleavage along crystal planes or along grain boundaries
   C. shearing at 45 degrees
   D. slow creep
   Answer: B. Cleavage. (Key point: Brittle)

3. Which promotes brittle fracture?
   A. High temperature
   B. Slow loading
   C. Low temperature, high strain rate, notches
   D. Smooth surfaces
   Answer: C. Listed in the answer. (Key point: Promoting factors)

## Related in Civil Engineering Materials

- [Tensile test numerical, 40 mm specimen](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Anumerical-tensile-test-40mm) — Civil Engineering Materials, chapter 1