Fatigue and Durability
Fatigue failure is a common design problem and potentially difficult to design for due to scatter in material property data and unknown input duty. When stresses, either derived from hand calculation or FEA, intended duty, and material properties are known, then an approximation of the fatigue life can be given. For high number of low amplitude loads, the Stress Life method is best employed and, conversely, for high load low infrequent loads, often the Strain Life technique is employed. Guidelines such as BS 7608 may also be drawn upon.
Matters Mechanical have experience with many fatigue hand calculations and utilizing nCode’s DesignLife to combine Rainflow analysis of more complex input duty cycles with the material properties to estimate life.
DeweSoft, data capture equipment has been used extensively to determine input signal for fatigue models.