Low cycle fatigue

Definition

Low cycle fatigue refers to the failure of materials under conditions of repeated loading and unloading that occurs within a relatively low number of cycles, typically less than 10,000. This type of fatigue is particularly relevant for components subjected to high stress levels and significant plastic deformations, often seen in mechanical systems experiencing fluctuating loads.

5 Must Know Facts For Your Next Test

1. Low cycle fatigue is characterized by significant plastic deformation in materials due to high stress and low cycle counts.
2. This type of fatigue often occurs in components like structural elements in machinery or aerospace applications that undergo frequent but intense loading conditions.
3. The Coffin-Manson relation is commonly used to describe the relationship between strain amplitude and the number of cycles to failure in low cycle fatigue scenarios.
4. Factors such as temperature, strain rate, and material microstructure can significantly influence the low cycle fatigue life of a component.
5. Designers often incorporate safety factors and material selection strategies to mitigate the effects of low cycle fatigue in critical components.

Review Questions

• How does low cycle fatigue differ from high cycle fatigue in terms of loading conditions and material response?
  • Low cycle fatigue differs from high cycle fatigue primarily in the number of load cycles and the stress levels experienced by materials. In low cycle fatigue, materials are subjected to high stress levels leading to significant plastic deformation and failure within fewer than 10,000 cycles. In contrast, high cycle fatigue occurs under lower stress conditions over many cycles, often resulting in elastic deformation. This distinction is crucial for engineers when designing components that will experience varying loading conditions.
• Discuss the importance of the Coffin-Manson relation in understanding low cycle fatigue behavior.
  • The Coffin-Manson relation plays a vital role in predicting low cycle fatigue behavior by establishing a correlation between strain amplitude and the number of cycles to failure. This relationship helps engineers estimate how many cycles a component can endure under specific loading conditions before succumbing to failure. Understanding this relationship allows for better material selection and design strategies to enhance the durability and performance of components exposed to cyclic loading.
• Evaluate how factors like temperature and strain rate can affect the low cycle fatigue life of a material, and propose strategies for mitigating these effects in design.
  • Temperature and strain rate are critical factors influencing the low cycle fatigue life of materials. High temperatures can lead to softening and reduced strength, while high strain rates may increase material hardening effects. To mitigate these issues in design, engineers can select materials with higher temperature resistance or employ heat treatment processes to enhance strength. Additionally, designing components with improved geometries or using surface treatments can help minimize stress concentrations that contribute to early failure due to low cycle fatigue.

Related terms

high cycle fatigue: High cycle fatigue involves the failure of materials subjected to a large number of cycles, generally exceeding 10,000, where the stress levels are relatively low and the material primarily experiences elastic deformation.

fatigue limit: The fatigue limit is the maximum stress level below which a material can withstand an infinite number of load cycles without failing, often associated with high cycle fatigue scenarios.

cyclic loading: Cyclic loading refers to the application of repeated load or stress on a material over time, leading to fatigue failure when the material cannot withstand these repeated forces.