Fatigue

Definition

Fatigue is the gradual weakening of a material due to repeated loading and unloading cycles, leading to the eventual failure of the material. This phenomenon is critical in engineering, as materials and structures often experience varying loads over time, making understanding fatigue essential for safety and reliability.

5 Must Know Facts For Your Next Test

1. Fatigue is responsible for a significant number of structural failures, particularly in aerospace applications where components undergo repeated loading during flight cycles.
2. The fatigue process usually involves three stages: crack initiation, crack propagation, and final failure, each contributing to the overall lifespan of a component.
3. Factors affecting fatigue life include material properties, environmental conditions, surface finish, and stress concentrations.
4. Engineers often conduct fatigue testing to determine the endurance limit of materials, which indicates the maximum stress level a material can withstand for an infinite number of loading cycles without failing.
5. Understanding fatigue allows engineers to design safer structures by incorporating safety factors and selecting materials with appropriate fatigue resistance.

Review Questions

• How does cyclic loading contribute to the phenomenon of fatigue in materials?
  • Cyclic loading plays a crucial role in fatigue by subjecting materials to repeated stress variations over time. This repeated stress can cause microscopic cracks to initiate and grow within the material. As the number of cycles increases, these cracks can propagate until they reach a critical size, leading to material failure. Understanding this relationship helps engineers anticipate potential failure points in structures subjected to regular loads.
• Discuss how an S-N curve is used in assessing material performance regarding fatigue.
  • An S-N curve provides essential insights into a material's fatigue performance by plotting applied stress levels against the number of cycles until failure. By analyzing this curve, engineers can identify endurance limits for different materials and predict how long a component might last under specific load conditions. This information is vital when designing components that must withstand cyclic loading without succumbing to fatigue-related failures.
• Evaluate the impact of environmental factors on fatigue life in aerospace materials and structures.
  • Environmental factors such as temperature, humidity, and exposure to corrosive agents significantly affect the fatigue life of aerospace materials. For instance, high temperatures can accelerate crack growth rates, while corrosive environments can lead to stress corrosion cracking, further reducing fatigue life. Engineers must consider these factors during design and material selection to ensure that components can withstand real-world conditions while maintaining their integrity over time.

Related terms

Cyclic Loading: A type of loading where a material is subjected to repeated or fluctuating stresses, often leading to fatigue.

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

Fracture Mechanics: The study of how cracks propagate in materials and how they can lead to failure, which is important for understanding fatigue failures.