Question

The stress ratio for completely reversed fatigue cycle is:

• A. 1
• B. 0.5
• C. -1
• D. -0.5

Hint:

For a completely reversed fatigue cycle, maximum and minimum stresses are equal and opposite, giving a stress ratio \( R = -1 \).

Answer 1

The Correct Option is C

The stress ratio (\( R \)) in fatigue loading is defined as: \[ R = \frac{\sigma_{min}}{\sigma_{max}} \] where \( \sigma_{min} \) is the minimum stress and \( \sigma_{max} \) is the maximum stress in a cycle.
In a completely reversed fatigue cycle, the material experiences equal magnitude of tensile and compressive stresses, but in opposite directions. That is: \[ \sigma_{min} = -\sigma_{max} ⇒ R = \frac{-\sigma_{max}}{\sigma_{max}} = -1 \] This condition is commonly used in fatigue testing to simulate conditions of alternating loading.
Other options such as:
- \( R = 1 \): mean stress loading (no reversal),
- \( R = 0.5 \): partially reversed with minimum stress still tensile,
- \( R = -0.5 \): not fully reversed,
do not correspond to the completely reversed scenario.