Block-Program-Volume Effect-Henry Approach

4 Block-Program-Volume Effect-Henry Approach 

Reference is made to the previous sample problem 3. Calculate the minimum section of the beam to withstand with 99.9 % probability of survival at least 10 unit reference blocks using Miner s rule and Marin approach. Let s proceed by trial and error. Increase the section thickness from 10 to 11 mm. the stress state will be 

Just increasing the thickness by one millimeter has resulted in a 10 folds increase in fatigue life. Let s use, now, the Henry approach described by Eq. (8.23). Apply the 245 Mpa stress ampUtude package first. The new reduced fatigue life is 

The first package of cycles will reduce the fatigue limit to zero, which actually means that there is no room for any other package of cycles. According to Henry, then, the beam cannot withstand 20 unit blocks. Let try to reduce the number of blocks to 10, then 

This time the beam will withstand the fatigue cycles. Increasing the number of blocks to 13 it yields 

---