Low-cycle fatigue

Definition

Low-cycle fatigue refers to the failure of materials due to cyclic loading at relatively low numbers of cycles, typically less than 10,000. This type of fatigue occurs when a material is subjected to high levels of stress that lead to significant plastic deformation, making it distinct from high-cycle fatigue, where the stresses are lower and the number of cycles is higher. Understanding low-cycle fatigue is crucial in assessing the durability and longevity of components subjected to fluctuating loads, especially in critical engineering applications.

5 Must Know Facts For Your Next Test

1. Low-cycle fatigue is primarily characterized by plastic deformation that accumulates with each loading cycle, which leads to eventual failure.
2. This type of fatigue is often observed in components that experience high-stress fluctuations, such as turbine blades and structural frames in buildings.
3. The initiation phase of low-cycle fatigue can occur after a relatively small number of cycles due to high strain levels, making early detection critical.
4. Factors such as temperature, material properties, and environmental conditions can significantly influence the low-cycle fatigue behavior of materials.
5. Common methods for predicting low-cycle fatigue life include using strain-life or stress-life approaches based on experimental data.

Review Questions

• How does low-cycle fatigue differ from high-cycle fatigue in terms of stress levels and number of cycles?
  • Low-cycle fatigue occurs at higher stress levels and typically involves fewer than 10,000 loading cycles, leading to significant plastic deformation. In contrast, high-cycle fatigue operates under lower stress levels with a much larger number of cycles, often exceeding 10,000. The key difference lies in how the material responds; low-cycle fatigue emphasizes plastic deformation while high-cycle focuses on elastic behavior.
• Discuss how environmental factors can impact the low-cycle fatigue performance of materials.
  • Environmental factors such as temperature, humidity, and corrosive elements can significantly affect the low-cycle fatigue performance of materials. For example, elevated temperatures may accelerate degradation processes or alter material properties, potentially leading to premature failure. Additionally, corrosive environments can exacerbate crack initiation and propagation by weakening material integrity, making it essential to consider these factors when designing components for specific applications.
• Evaluate the importance of understanding low-cycle fatigue in the design of engineering components subjected to dynamic loads.
  • Understanding low-cycle fatigue is vital in designing engineering components that must endure dynamic loads because it helps engineers predict failure points and enhance reliability. By analyzing factors such as loading conditions and material properties, engineers can implement design modifications or select appropriate materials that mitigate the risk of low-cycle fatigue failure. This proactive approach ultimately leads to safer structures and machinery while reducing maintenance costs and downtime.

Related terms

Cyclic loading: The application of repeated loads on a material, which can cause fatigue failure over time due to the buildup of stress and strain.

Plastic deformation: A permanent change in shape that occurs when a material is subjected to stress beyond its yield 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 given material.