---
title: "Define fatigue in brief"
subject: "Civil Engineering Materials"
chapter: 1
key: "semester_3/civil_engineering_materials:property-fatigue"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/property-fatigue
site: BCT Engineering
---

# Define fatigue in brief

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

- Asked in: 2079 Bhadra, 1 marks; 2074 Chaitra, 2 marks; 2068 Baisakh (asked 3 times)
- Video: [Understanding Fatigue Failure and S-N Curves](https://www.youtube.com/watch?v=o-6V_JoRX1g) — The Efficient Engineer
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/property-fatigue
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-1

## Question

Define fatigue as a property of materials.

## Short answer

Fatigue is failure under repeated cyclic stresses, with crack initiation, growth and sudden fracture even at stresses below ultimate strength. The stress below which a material can withstand infinite cycles is the endurance limit.

## Answer

**Fatigue** is the failure of a material under repeated or fluctuating (cyclic) stresses, even when the maximum stress is much lower than the ultimate tensile strength.

Failure starts as a tiny crack at a point of stress concentration, grows with every load cycle and ends in sudden fracture. The stress below which a material can bear an infinite number of cycles is called the **endurance (fatigue) limit**. Fatigue is important for bridges, crane girders, railway tracks and machine parts.

## Check yourself

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

1. Fatigue failure is caused by
   A. repeated or fluctuating stresses
   B. a single slow static load
   C. high humidity
   D. chemical attack alone
   Answer: A. Fatigue is failure under cyclic stress. (Key point: Definition)

2. In fatigue, failure can occur at a maximum stress that is
   A. above the ultimate strength only
   B. much lower than the ultimate tensile strength
   C. exactly equal to yield only
   D. zero
   Answer: B. Fatigue failure occurs even at stresses well below ultimate strength. (Key point: Stress level)

3. How does a fatigue failure develop?
   A. Uniform necking over the whole length
   B. Gradual melting
   C. A tiny crack at a stress concentration grows with each cycle and ends in sudden fracture
   D. Slow creep with no crack
   Answer: C. Crack starts at a stress concentration and grows per cycle. (Key point: Mechanism)

4. The endurance limit is the stress
   A. at which a material yields
   B. at which creep starts
   C. at first cycle fracture
   D. below which infinite cycles can be borne
   Answer: D. Below the endurance limit the material survives an infinite number of cycles. (Key point: Endurance limit)

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