How do you determine the fatigue life of a material under repeated stress?

2 Fatigue Testing

Fatigue testing is a practical approach to evaluate a material's fatigue life. This process involves subjecting a specimen to controlled stress cycles until failure occurs. The results from these tests are plotted on an S-N curve (stress versus number of cycles to failure), which shows the relationship between stress amplitude and fatigue life. By analyzing the S-N curve, you can predict how long a material will last under similar stress conditions in actual use.

3 Crack Growth

Monitoring crack growth is a vital aspect of fatigue life prediction. Small cracks can form and propagate in a material under cyclic loading, eventually leading to failure. By understanding the rate at which these cracks grow, you can estimate the remaining life of a component. Techniques like fracture mechanics are used to model crack growth and predict the point at which a crack will reach a critical size, causing catastrophic failure.

4 Material Properties

The inherent properties of a material play a significant role in its fatigue life. Factors such as composition, microstructure, and heat treatment can affect a material's resistance to fatigue. It's important to consider these properties when selecting materials for applications that involve cyclic loading. Materials with higher fatigue strength are more suitable for such applications as they can endure more stress cycles before failing.

5 Design Factors

Design factors also influence the fatigue life of a material. Features like notches, holes, and sharp corners can concentrate stress and reduce fatigue life. You must take these design stress concentrators into account when assessing fatigue life. Using design modifications like fillets or stress-relief features can improve fatigue performance by reducing localized stress concentrations.

6 Operational Conditions

Lastly, operational conditions such as temperature, corrosive environments, and loading frequency can significantly impact fatigue life. Materials may exhibit different fatigue characteristics under varying conditions. For example, high temperatures can accelerate material degradation and reduce fatigue life. It's crucial to simulate or consider these operational factors when determining the expected fatigue life of a material in its intended application.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?