Fatigue Damage Under Narrow-Band Random Processes

2 Fatigue Damage Under Narrow-Band Random Processes 

By using the Basquin-based expression (8.47), the fatigue damage is then 

Equation (8.49) is based on a prff expression derived from the cycles ratio given by Eq. (8.47). There is another expression for the prff based on the PSD. For the narrow-band process this expression is 

Assuming as cumulative probability function the Weibull expression P df) given by Eq. (4.45), then the expected value of will be 

In deriving Eqs. (8.50) or (8.55) it has been assumed that all stress cycles have a mean value equal to zero. If a mean stress exists it must be taken into consideration. According to Miner s rule (see Sect. 8.3.1) failure occurs when D —. However, a shortcoming of Miner s rule is that damage does not progress and accumulate in linear fashion (see Sect. 8.3.2). 

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