Calculating Fatigue Life for Variable Stress in Cast Aluminum

In summary, fatigue life is the number of cycles or stresses a material can withstand before failing under repeated loading. It is calculated using the stress-life approach and can be affected by factors such as material properties, environmental conditions, and design and loading conditions. While fatigue life calculations can provide a good estimation, they may not always be accurate due to various factors. To improve fatigue life, materials with higher fatigue strength can be selected, surface treatments can be applied, and design modifications and proper maintenance can be implemented.
  • #1
rikcardo
5
0
Hello

How can I calculate the fatigue life of a variable stress between 0 and 90 MPa in cast aluminum?

Do I use the mean stress and compare it with the wohler curve? what is the logic of using the mean stress? Why not the maximum stress?

Do I have to use the Goodman or Gerber diagram?

Any advise on literature or websites about this topic?

Thank you in advance
 
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  • #2
Try the Soderberg Line. See Equation 50.31, "Mechanical Engineering Reference Manual for the PE," 10th Edition.
 

1. What is fatigue life?

Fatigue life is a measure of the number of cycles or stresses a material can withstand before it fails under repeated loading. It is an important factor to consider in the design and selection of materials for applications that involve cyclic loading, such as machinery, vehicles, and structures.

2. How do you calculate fatigue life?

The most commonly used method for calculating fatigue life is the stress-life (S-N) approach. This involves plotting the stress amplitude (S) against the number of cycles to failure (N) on a log-log scale and determining the slope of the resulting curve. The fatigue life can then be calculated using the formula: N = (S/σe)m, where σe is the material's endurance limit and m is the slope of the curve.

3. What factors affect fatigue life?

Fatigue life can be affected by a variety of factors, including the material's strength, hardness, microstructure, surface finish, and environmental conditions such as temperature and corrosion. The design and loading conditions can also have a significant impact on fatigue life.

4. Can fatigue life be predicted accurately?

While fatigue life calculations provide a good estimation, it is important to note that they are not always accurate. This is because fatigue life can be affected by a multitude of factors, some of which may not be fully understood or accounted for in the calculations. Therefore, it is essential to use caution when relying solely on fatigue life calculations for critical applications.

5. How can fatigue life be improved?

There are several ways to improve fatigue life, including selecting materials with higher fatigue strength or using surface treatments to increase resistance to fatigue. Design modifications, such as reducing stress concentrations and providing smoother transitions, can also improve fatigue life. Additionally, proper maintenance and inspection can help detect and mitigate potential sources of fatigue failure.

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