Alternating Stresses

 

*      Definition:

o       An Alternating Stress is associated with a CYCLIC force, torque, or bending being applied to a component.  Our primary concern for this project is axial and bending loads.

 

 

                                      

 

 

*      The Alternating Stress is defined by the equation below:

o       Axial Loading

§         σ = F/A

 

o       Bending

§         σ = M*y/I

 

o       These Formulas come from basic mechanics and can be analysed using any Mechanics of Materials text.

 

  Goodman Approach

 

*      Mean Stress is the average stress that is applied to the member and can be calculated using the following equation:

                         

σm = (σmax + σmin)/2

 

 

 

*      Stress Amplitudes can similarly be defined using the following equation:

 

σa = (σmax – σmin)/2