Fatigue life

Definition

Fatigue life refers to the number of cycles a material or structure can endure before failure occurs due to repeated stress or loading. This concept is crucial in assessing how long a material can perform under conditions that involve fluctuating or cyclic stresses, ultimately determining its reliability and safety in practical applications.

5 Must Know Facts For Your Next Test

1. Fatigue life is significantly influenced by factors such as material properties, surface finish, loading conditions, and environmental factors like temperature and corrosion.
2. Testing for fatigue life often involves subjecting materials to controlled cyclic loading until failure occurs, which helps establish their fatigue limits.
3. Materials with a higher endurance limit typically have longer fatigue lives, making them more suitable for applications involving repetitive loads.
4. The S-N curve is an essential tool for predicting fatigue life, allowing engineers to assess the reliability of materials under various stress levels.
5. Understanding fatigue life is crucial in designing components in industries like aerospace and automotive, where safety and performance are critical.

Review Questions

• How does the concept of fatigue life relate to material selection in engineering applications?
  • When engineers select materials for applications that will experience cyclic loading, they must consider the fatigue life of those materials. A material with a longer fatigue life is preferable as it indicates greater durability and reliability under repeated stresses. This consideration is especially important in industries such as aerospace and automotive, where component failures can lead to catastrophic consequences.
• Discuss the significance of the S-N curve in understanding fatigue life and its implications for engineering design.
  • The S-N curve plays a vital role in understanding fatigue life by providing a visual representation of how a material's strength decreases with increasing cycle counts. It allows engineers to predict how long a component will last under specific stress levels. By analyzing the S-N curve, engineers can make informed design choices to ensure that materials chosen for critical components have sufficient fatigue resistance, enhancing overall safety and performance.
• Evaluate how environmental factors might influence the fatigue life of materials in real-world applications.
  • Environmental factors such as temperature fluctuations, humidity, and corrosive substances can significantly impact the fatigue life of materials. For instance, elevated temperatures may weaken a material's structure, leading to premature failure under cyclic loading. Similarly, corrosive environments can degrade materials over time, reducing their fatigue resistance. In engineering design, it is crucial to account for these factors to ensure that materials will perform reliably throughout their intended lifespan, ultimately enhancing safety and performance.

Related terms

Endurance limit: The maximum stress level a material can withstand indefinitely without experiencing fatigue failure.

Cyclic loading: The application of varying loads on a material over time, which can lead to fatigue failure if the load exceeds the material's fatigue strength.

S-N curve: A graphical representation that shows the relationship between the number of cycles to failure (N) and the applied stress (S) for a material.