Endurance Limit
The endurance limit is the maximum stress amplitude a material can endure indefinitely under cyclic loading without experiencing fatigue failure. It is most commonly observed in ferrous materials, such as steel and iron, and some alloys.
- Defining Characteristics
- The endurance limit is the horizontal asymptote on the S-N curve. Stress amplitudes below this level allow the material to survive an infinite number of cycles.
- For non-ferrous materials (e.g., aluminum, copper), an endurance limit is generally not observed, and fatigue strength is instead specified for a finite number of cycles (e.g., 10⁶ or 10⁷ cycles).
- Material Behavior
- For materials with an endurance limit (e.g., steels), the curve flattens out after a certain number of cycles, typically around 10⁶ cycles.
- Non-ferrous materials show a continuously decreasing S-N curve, meaning that failure can occur at any stress level given enough cycles.
- Factors Influencing the Endurance Limit
- Surface Finish: Smoother surfaces reduce stress concentrators and increase the endurance limit.
- Environmental Conditions: Corrosion or temperature fluctuations can degrade the endurance limit.
- Size and Geometry: Larger cross-sections and sharp corners act as stress concentrators, reducing the endurance limit.
- Engineering Applications
- The concept of the endurance limit is crucial in designing components that are subjected to cyclic loading, such as:
- Rotating shafts
- Springs
- Gears
- Engineers design for stresses below the endurance limit to ensure infinite fatigue life for these components.
- The concept of the endurance limit is crucial in designing components that are subjected to cyclic loading, such as:
